The photoelectric effect is the ejection of electrons from a metal surface.
What is the photoelectric effect?
Blue light has a higher frequency and therefore a higher energy than red light and can therefore eject electrons from a metal that red light cannot.
Why does blue light eject electrons from a certain photosensitive surface, whereas red light has no effect on that surface?
Yes, bright blue light will eject more electrons than dim light of the same frequency.
Will bright blue light eject more electrons than dim light of the same frequency?
The photoelectric effect supports the particle model of light because it indicates collisions between the metal surfaces and photons.
Does the photoelectric effect support the particle model or the wave model of light?
Protons and neutrons are nucleons.
Which of the following are nucleons- protons, neutrons, or electrons?
Electrical forces tend to push a nucleus apart.
Do electrical forces tend to hold a nucleus together or push it apart?
The nuclear strong force reacts betweens the neutrons.
Between what kinds of particles does the nuclear strong force act?
The electric force has a stronger range.
Which force a longer range, the electric force or the strong force?
A neutron is unstable when it is not near a proton.
When is a neutron unstable?
Alpha rays have a positive electric charge, beta rays are negative, and gamma rays are electrically neutral. Alpha rays are helium nuclei, beta particles are electrons, and gamma rays are electromagnetic radiation.
Distinguish among alpha, beta, and gamma rays.
Alpha rays have the least penetrating power, beta particles have the second least penetrating power, and gamma rays have the highest penetrating power.
How do the penetrating powers of the three types of radiation compare?
An ion is charged due to loss of gain of electrons. Isotopes differ in the number of neutrons they have.
Distinguish between an ion and an isotope.
In a normal atom, the number of electrons is equal to the number of protons.
How does the number of electrons in a normal atom compare with the number of protons in its nucleus?
U-238 has the greater number of neutrons.
Which isotope has the greater number of neutrons, U-235 or U-238?
Half of the substance will be left after 1620 years, one fourth of the substance will be left after 3240 years.
If the radioactive half-life of a certain isotope is 1620 years, how much of that substance will be left t the end of the 1620 years? After 3240 years?
If either an alpha or beta particle is ejected, then it does become a completely different element. If a gamma ray is ejected, it does not.
When an atom undergoes radioactive decay, does it become a completely different element?
a. The atomic number would decrease by 2.
b. The atomic mass number would decrease by 4.
b. The atomic mass number would decrease by 4.
a. What happens to the atomic number of an atom when it ejects an alpha particle?
b. What happens to its atomic mass number?
a. The atomic number increases by 1.
b. The atomic mass number stays the same.
b. The atomic mass number stays the same.
a. What happens to the atomic number of an atom when it ejects a beta particle?
b. What happens to its atomic mass number?
a. It becomes Radium
b. It becomes Protactinium.
b. It becomes Protactinium.
a. What element does thorium become if it emits an alpha particle?
b. What if it emits a beta particle?
In order to use carbon dating there must be carbon present in the material, and there is no carbon in old coins.
Why would the carbon dating method be useless in dating old coins but not old pieces of adobe bricks?
There are deposits of lead in all deposits of uranium ore because over time, uranium decays into lead.
Why are there deposits of lead in all deposits of uranium ore?
The mass becomes the kinetic energy of the new particle.
What becomes of the loss in mass when light atoms fuse to become heavier ones?
Fusion reactors are not a present-day reality like fission reactors because fusion requires very high temperature and pressure. There are yet to be any sustained fusion reactions.
Why are fusion reactors not a present-day reality like fission reactors?
The mass of the atomic nucleus is less than the mass of the nucleons that compose it.
Is the mass of an atomic nucleus greater or less than the total mass of the nucleons that compose it?
total number of nucleons (neutrons and protons) in the nucleus of an atom
atomic mass number
number of protons in the nucleus of an atom
atomic number
Electric charges are similar to magnetic poles for they can both attract and repel without touching.
What do electric charges have in common with magnetic poles?
Charges can be isolated and poles cannot.
What is a major difference between electric charges and magnetic poles?
A piece of iron can be induced into becoming a magnet by simply placing it in a strong magnetic field. If you place a paperclip near a magnet, it itself will become a magnet because the domains become aligned in the magnetic field.
How can a piece of iron be induced into becoming a magnet? For example, if you were to place a paper clip near a magnet, it will itself become a magnet. Why?
If a current-carrying wire is bent into a loop, the magnetic field is stronger inside the loop than outside the loop because the magnetic fields become bunched up inside the loop.
If a current-carrying wire is bent into a loop, why is the magnetic field stronger inside the loop than outside?
A charged particle must be moving to experience a magnetic force.
What must a charged particle be doing in order to experience a magnetic force?
The magnetic field of Earth deflects many charged particles that make up cosmic radiation.
What role does Earth’s magnetic field play in cosmic ray bombardment?
The direction in which a current-carrying wire is forced when in a magnetic field is the same as the direction that moving particles are forced.
How does the direction in which a current-carrying wire is forced when in a magnetic field compare with the direction that moving charges are forced?
An electric field surrounds a stationary charge. A magnetic field and an electric field surround a moving electric charge.
What kind of field surrounds a stationary electric charge? A moving electric charge?
It is unlikely that Earth’s core is a permanent magnet because it is too hot for individual atoms to remain aligned.
Earth’s core is probably composed of iron and nickel, excellent materials for making permanent magnets. Why is it unlikely that Earth’s core is a permanent magnet?
The armature rotates because of an external source of energy such as fuel, wind, or water.
The armature of a generator must rotate in order to induce voltage and current. What causes the rotation?
A transformer actually transforms voltage and current.
What does a transformer actually transform- voltage, current, or energy?
60 volts will be induced in the secondary coil.
If the number of secondary turns is 10 times the number of primary turns, and the input voltage to the primary is 6 volts, how many volts will be induced in the secondary coil?
a. If slight power losses due to heating of the core are neglected, the power input to the primary coil will equal the power output of the secondary coil.
b. The product of voltage and current in the primary is equal to the product of voltage and current in the secondary.
b. The product of voltage and current in the primary is equal to the product of voltage and current in the secondary.
a. In a transformer, how does the power input to the primary coil compare with the power output of the secondary coil?
b. How does the product of voltage and current in the primary compare with the product of voltage and current in the secondary?
All electromagnetic waves travel at the same speed, the speed of light.
How do the wave speeds compare for high frequency and low frequency electromagnetic waves?
An electric generator turns movement into electricity; an electric motor turns electricity into movement.
What is the basic difference between and electric generator and an electric motor?
Accelerating charges
What is the source of all electromagnetic waves?
A transformer requires alternating currents to create a change required to produce induction
Why does a transformer require alternating voltage?
No, an efficient transformer cannot step up energy because that would violate the law of conservation of energy.
Can an efficient transformer step up energy? Defend your answer.
Vprimary/# primary turns = Vsecondary/# secondary turns
9 V/ 1= 36 V/4
12 V / 1= ? V/4
Vsecondary = 48 V
A transformer has an input of 9 volts and an output of 36 volts. If the input is changed to 12 volts, what will the output be?
Vprimary/# primary turns = Vsecondary/# secondary turns
120 V/ 500 turns = 12 V/ ? turns
# of secondary turns = 50
A portable CD player requires 12 volts to operate correctly. A transformer nicely allows the device to be powered from a 120-volt outlet. If the primary has 500 turns, how many turns should the secondary have?
8.2 x 10-8 N
Calculate the electric force between two electrons that are 5.3 x 10-11 m apart (electron charge = -1.6 x 10-19 C).
voltage
What is considered to be the “push” or “pressure” that is applied in an electric circuit?
produced by a generator.
Alternating current is
12.2 A
Calculate the total current in a circuit with 2-ohm, 4-ohm, 3-ohm resistors connected in series with a 110-V source.
The voltage would increase by a factor of 2.
What would happen if the coil of an electromagnet were increased so that there were twice as many coils?
can increase or decrease voltage to a device
A transformer____________________.
P= IV
P=(9.5)(1.2)
P=(9.5)(1.2)
P=11.4 W
Calculate the amount of power used by a portable DVD player that uses 9.5 volts and 1.2 amperes. Show all work including formulas and units.
Coulomb’s law: F=(kq1q2)/d^2
Law of Universal Gravitation: F= G(m1m2)/r^2
Coulomb’s law allows for attraction and repulsion and gravitation is only attraction. both forces are dependent on the square of the distance between them. Both have a constant.
Write the formula for Coulomb’s Law and the Law of Universal Gravitation. Compare and contrast the two laws.
Both magnets and charges have poles. Both opposites attract and likes repel. Electric charges can be isolated, but magnetic poles cannot. Charges can be positive or negative; magnets have north and south poles.
How are magnets similar to charges? How are they different?
magnet with a field produced by electric current; usually in the form of a wire coiled around a piece of iron
electromagnet
a force field that fills the space around every magnet or current-carrying wire
magnetic field
one of the regions on a magnet that produces magnetic forces
magnetic pole
Induced voltage in a coil is proportional to the product of the number of loops and the rate at which the magnetic field changes within the loops
Faraday’s law
a machine that produces electric current by rotating a coil within a stationary magnetic field
generator
a device for increasing or decreasing voltage through electromagnetic induction
transformer
120 J per coulomb are given to charges that flow in a 120-volt circuit.
How many joules per coulomb are given to charges that flow in a 120-volt circuit?
The third prong connects the body of the appliance directly to ground. Any charge that builds up on an appliance is therefore conducted to the ground.
What is the function of the third prong in a household electric plug?
I = amperes q = couombs t = time
I= q/t
I= 10/5
I= q/t
I= 10/5
I=2 amperes
Calculate the current where 10 coulombs of charge pass a point in 5 seconds.
I = V/R
I = 240/60
I = 240/60
I = 4 amperes
Calculate the current in the coiled heating element of a 240-V stove. The resistance of the element is 60 ohms at its operating temperature.
I = V/R
0.4=3/R
0.4=3/R
R= 7.5 ohms
Calculate the resistance of the filament in a lightbulb that carries 0.4 A when 3.0 V is impressed across it.
No, an ampere measures electric current and a volt measures electric potential. Electric current is a flow and electric potential is the cause of the flow.
Do an ampere and a volt measure the same thing, or different things? What are those things, and which is a flow and which is the cause of the flow?
Thick wires rather than thin wires are used to carry large currents because they have less resistance so they wont heat up as much as thin wires.
Why are thick wires rather than thin wires used to carry large currents?
An electric drill operating on a very long extension cord will not operate as fast as one operated on a short cord because longer wires have more resistance than shorter ones. As the resistance increases, the voltage decreases and so does the power.
Why will an electric drill operating on a very long extension cord not rotate as fast as one operated on a short cord?
The current in a light bulb connected to 220 V will be 2 times more than when the same bulb is connected to 110 V.
Will the current in a lightbulb connected to 220 V be more or less when the same bulb is connected to 110 V? How much?
There is no effect on current if both the voltage and the resistance are doubled or halved.
What is the effect on current if both the voltage and the resistance are doubled? If both are halved?
You would expect to find DC in the dome lamp in an automobile and AC in a lamp in your home.
Would you expect to find DC or AC in the dome lamp in an automobile? In a lamp in your home?
In a 60-Hz alternating current, an electron changes its direction 120 times.
In 60-Hz alternating current, how many times per second does an electron change its direction? (Don’t say 60!)
The 40 W light bulb has the greater filament resistance because P = IV, so a lower power output implies a lower current and therefore a higher filament resistance.
Two light bulbs designed for 120-V use are rated at 40 W and 60 W. Which lightbulb has the greater filament resistance? Why?
In a series circuit, electric devices form a single pathway for electron flow. In a parallel circuit, electric devices form branches, each of which provides a separate path for the flow of electrons.
Distinguish between a series circuit and a parallel circuit.
If three lamps are connected in series to a 6-volt battery, 2 volts are impressed across each lamp.
If three lamps are connected in series to a 6-volt battery, how many volts are impressed across each lamp?
If one of three lamps blows out when connected in series, the flow of electrons ceases.
If one of three lamps blows out when connected in series, what happens to the current in the other two?
If three lamps are connected in parallel to a 6-volt battery, 6 volts are impressed across each lamp.
If thee lamps are connected in parallel to a 6-volt battery, how many volts are impressed across each lamp?
If one of three lamps blows out when connected in parallel, there is no break in the current of the other two.
If one of three lamps blows out when connected in parallel, what happens to the current in the other two?
a. There will be more current in each of three lamps if they are connected in parallel.
b. There will be more voltage across each lamp if they are connected in parallel.
b. There will be more voltage across each lamp if they are connected in parallel.
a. In which case will there be more current in each of three lamps- if they are connected to the same battery in series or in parallel?
b. In which case will there be more voltage across each lamp?
When more devices are added to a series circuit, the total circuit resistance increases. When more devices are added to a parallel circuit, the total circuit resistance decreases.
What happens to the total circuit resistance when more devices are added to a series circuit? To a parallel circuit?
The equivalent resistance of a pair of 8-ohm resistors in series is 16 ohms. The equivalent resistance of a pair of 8-ohm resistors in parallel is 4 ohms.
What is the equivalent resistance of a pair of 8-ohm resistors in series? In parallel?
The total circuit resistance decreases when more devices are added to a parallel circuit because there are more paths for the current to take.
Why does the total circuit resistance decrease when more devices are added to a parallel circuit?
Lines carrying an unsafe amount of current are overloaded.
What does it mean when you say that lines in a home are overloaded?
The function of a fuse or circuit breaker in a circuit is to prevent overloading.
What is the function of a fuse or a circuit breaker in a circuit?
As more devices are connected to the lines, more pathways are provided for current, lowering the combined resistance of this circuit. Therefore, a greater amount of current occurs in these lines. The resulting heat of overloaded lines may be sufficient to melt the insulation and start a fire.
Why will too many electric devices operating at one time often blow a fuse or trip a circuit breaker?
A short circuit is a circuit that has a path of much less resistance and therefore the current only takes that path.
What is meant by a short circuit?
Term applied to portions of an electric circuit that are connected at two points and provide alternative paths for the current between these two points.
in parallel
Term applied to portions of an electric circuit that are connected in a row so that the current that goes through one must go through all of them.
in series
The comparable property that underlies electrical forces is charge.
Gravitational forces depend on the property called mass. What comparable property underlies electrical forces?
A proton has more mass.
Which has more mass- a proton or an electron?
There are an equal number of protons and electrons in a normal atom.
In a normal atom, how many electrons are there compared with protons?
A negative ion has more electrons than protons whereas a positive ion has more protons than electrons.
How does a negative ion differ from a positive ion?
Because astronomical objects have very large masses, gravity has a greater effect on them.
Why does the weaker force of gravity dominate over electrical forces for astronomical objects?
A good conductor allows the movement of electrons and a good insulator stops the movement of electrons.
What is the difference between a good conductor and a good insulator?
a. The three main methods of charging are charging by contact, charging by friction, and charging by induction.
b. Charging by induction requires no touching.
b. Charging by induction requires no touching.
a. What are the three main methods of charging objects?
b. Which method involves no touching?
When one side of the atom or molecule is induced to be slightly more positive (or negative) than the other side, it is said to be electrically polarized.
What does it mean to say an object is electrically polarized?
When their separation distance is doubled, the electrical force is reduced by a factor of 4. When tripled, it is reduced by a factor of 9.
By how much is the electrical force between a pair of ions reduced when their separation distance is doubled? Tripled?
You are positively charged, the comb is negatively charged.
If you scuff electrons from your hair onto a comb, are you positively or negatively charged? How about the comb?
The leaves spring apart because they have charges of the same sign and repel each other.
An electroscope is a simple device. It consists of a metal ball that is attached by a conductor to two fine gold leaves that are protected from air disturbances in a jar, as shown in the sketch. When the ball is touched by a charged object, the leaves that normally hang straight spring apart. Why?
Both heat and electricity are conducted through the movement of electrons.
Why is a good conductor of electricity also a good conductor of heat?
When a charged object is brought close to an electrically neutral object, the particles carrying the same charge repel each other, creating an induced charge in the neutral object.
Explain how an object that is electrically neutral can be attracted to an object that is charged.
The electron would have the greater speed because it has the smaller mass.
Imagine a proton at rest a certain distance from a negatively charged plate. Then imagine the similar case of an electron at rest, the same distance away, from a plate of equal and opposite charge. In which case would the moving particle have the greater speed when the collision occurs? Why?
Action at a distance means an interaction between objects that are far apart.
What is meant by the expression action at a distance?
Both electrical and gravitational fields are a means of exerting forces.
How are a gravitational field and an electric field similar?
An electrical field is considered a vector quantity because it has both direction and magnitude.
Why is an electric field considered a vector quantity?
Electrons from the lighting bolt mutually repel and spread over the outer metal surface of the car. Although the electric field they set up may be great outside the car, the overall electric field inside the car practically cancels to zero
Why are occupants safe inside a car struck by lightning?
a. There is no way to shield gravity because gravity only attracts.
b. Yes, electrical fields can be shielded.
b. Yes, electrical fields can be shielded.
a. Can gravity be shielded?
b. Can electric fields be shielded?
b. Can electric fields be shielded?
Doing work increases the object’s potential energy
What is the relationship between the amount of work you do on an object and its potential energy?
The electrical potential energy of a charged particle can be increased by pushing the charge against the electric field.
How can the electrical potential energy of a charged particle in an electric field be increased?
The electric potential energy will transform into kinetic energy.
What will happen to the electrical potential energy of a charged particle in a electric field when the particle is released and free to move?
The electric potential does not increase because if you increase both the electric potential energy and the charge, then the increase in each cancels out resulting in the same electric potential.
If you do more work to move more charge a certain distance against an electric field, and increase the electrical potential energy as a result, why do you not also increase the electric potential?
Electric potential can be high when electrical potential energy is relatively low if the charge is low as well.
How can electric potential be high when electrical potential energy is relatively low?
The inside surface is uncharged because all of the electrons move to the outside surface.
How does the amount of charge on the inside surface of the sphere of a charges Van de Graaff generator compare with the amount on the outside?
The electron will travel faster and in the opposite direction of the proton, reaching the plate first.
Imagine a “free” electron and “free” proton held midway between the plates of a charged parallel plate capacitor. When released, how do their accelerations and directions of travel compare? If we ignore their attraction to each other, which reaches a capacitor plate first?
It is correct to say that an object with twice the electric potential of another has twice the electrical potential energy only if the charges are the same.
Is it correct to say that an object with twice the electric potential of another has twice the electrical potential energy? Defend your answer.
Your hair stands out because each strand of hair becomes charged with the same sign, causing them to repel each other.
Why does your hair stand out when you are charged by a device such as a Van de Graaf generator?
a. Electric potential = electrical potential charge / charge
Electric potential = 12 J / 0.001 C
Electric potential = 12000 V
Electric potential = 12 J / 0.001 C
Electric potential = 12000 V
b. The principle of conservation of energy says that the energy released will be equal to the energy put into the system, so the kinetic energy of the charge as it flies back past its starting point will be 12 J.
a. If you do 12 J of work to push 0.001 C of charge from point A to point B in an electric field, what is the voltage difference between points A and B?
b. When the charge is released, what will be its kinetic energy as it flies back past its starting point A? What principle guides your answer?
A converging lens is thicker in the middle and rays of light that are initially parallel are made to converge. A diverging lens is thinner in the middle and the rays of light are made to diverge.
Distinguish between a converging lens and a diverging lens.
A virtual image cannot be seen on a screen at the image distance because no light is actually directed to the image position. The rays that reach your eye behave as if they came from the image position, however. A real image is formed when light from the object does converge and can be focused on a screen.
Distinguish between a virtual image and a real image.
The first ray runs parallel to the principal axis, the second ray runs directly through the center of the lens, and the third ray travels through the focal point and then parallel to the principal axis.
There are three convenient rays commonly used in ray diagrams to estimate the position of an image. Describe these three rays in terms of their orientation with respect to the principal axis and focus points.
The camera is most similar to the eye.
Which instrument- a telescope, a compound microscope, or a camera- is most similar to the eye?
The eyes of a farsighted person form images behind the retina because the eyeball is too short. Farsighted people have to hold things more than 25 cm away. A nearsighted person can see nearby objects clearly, but does not see distant objects clearly because they are focused to near the lens, in front of the retina. The eyeball is too long.
Distinguish between farsighted and nearsighted vision.
Astigmatism of the eye is a defect that results when the cornea is curved more in one direction than the other. Because of this defect the eye does not form sharp images. The remedy is cylindrical corrective lenses that have more curvature in one direction than another.
What is astigmatism, and how can it be corrected?
a) A converging lens will produce a virtual image only when the object is between the focal point and the lens.
b) A diverging lens will never produce a real image.
b) A diverging lens will never produce a real image.
(a) What condition must exist for a converging lens to produce a virtual image?
(b) What condition must exist for a diverging lens to produce a real image?
(b) What condition must exist for a diverging lens to produce a real image?
To demonstrate than an image was indeed real, you could show that it appears on a screen.
How could you demonstrate that an image was indeed a real image?
Because the images that are produced will be upside down if you do not, so by putting it upside down the image will appear right side up.
Why do you have to put slides into a slide projector upside down?
If light had the same speed in glass as in air, there would be no refraction, and therefore no focusing.
Would telescopes and microscopes magnify if light had the same speed in glass as in air? Explain.
a) If you narrow the opening waves will spread out more, producing a more pronounced shadow.
b) This spreading is called diffraction.
b) This spreading is called diffraction.
a. Waves spread out when they pass through an opening. Does spreading become more or less pronounced for narrower openings?
b. What is the spreading called?
Diffraction hinders the viewing of images in a microscope.
Does diffraction aid or hinder the viewing of images in a microscope?
Wave interference occurs for waves in general. Wave interference causes beat frequencies in sounds, as well as disturbances in ocean waves.
Does wave interference occur for waves in general, or only for light waves? Give examples to support your answer.
The bright fringes of light resulted from light waves from both holes arriving crest to crest (constructive interference-more light)
What is the cause of the fringes of light in Young’s experiment?
A diffraction grating is a multitude of closely spaced parallel slits.
What is a diffraction grating?
Iridescence is the colors produced by the interference of light waves of mixed frequencies in thin films. It is related to the phenomenon of interference.
What is iridescence, and to what phenomenon is it related?
The soap bubble will appear blue when illuminated by white light.
If a soap bubble is thick enough to cancel yellow by interference, what color will it appear if illuminated by white light?
Light emitted by a common lamp is incoherent, meaning it has many phases of vibration as well as many frequencies. A beam of light produced by a laser is coherent, meaning it has the same frequency, phase, and direction.
How does light from a laser differ from light from an ordinary lamp?
Because radio waves have longer wavelengths, they are able to diffract around buildings while light waves are not.
Why do radio waves diffract around buildings but light waves do not?
o = object distance i = image distance f = focal length
1/o + 1/I = 1/f
1/80 + 1/40 = 1/f
f = 26.7
26.7 cm
A far-sighted eye whose comfortable reading distance is 80 cm is to be supplied a corrective lens to enable reading at a normal distance of 40 cm. So the object distance is 80 cm and the image distance is 40 cm. What is the focal length of the corrective lens?
red and blue
What two colors of light will produce magenta?
refraction
The bending of light as it passes through one medium into another is called
virtual
What type of image do mirrors produce?
bending of a wave around a barrier
What is diffraction?
virtual and right-side up
A diverging lens will produce an image that is ___________________________.
47⁰
If a ray of light is incident on a mirror at an angle of 47⁰ to the normal, the angle of reflection is
light fringes indicate constructive interference
When monochromatic light waves interfere due to diffraction, ____________________.
radio waves (lowest frequency/longest wavelength)
visible light
x-rays (highest frequency/shortest wavelength)
visible light
x-rays (highest frequency/shortest wavelength)
List the following as they appear on the electromagnetic spectrum:
x-rays
visible light
radio waves
You should also indicate the direction of increasing frequency and the direction of increasing wavelength.
The atomic spectra is unique for each element.
Explain why the atomic spectra is considered the “fingerprint” of an element.
a device used to store charge in a circuit
capacitor
a force field that fills the space around every electric charge or group of charges
electric field
electrical potential energy per coulomb (J/C) at a location in an electric field; measured in volts and often called voltage
electric potential
energy a charge has due to its location in an electric field
electrical potential energy
a. A photon is a massless bundle of concentrated electromagnetic energy.
b. The photon is more consistent with the particle theory.
b. The photon is more consistent with the particle theory.
a. What is a photon?
b. Which theory of light is the photon more consistent with- the wave theory or the particle theory?
b. Which theory of light is the photon more consistent with- the wave theory or the particle theory?
It takes one year to travel the distance of one light-year.
How long does light take to travel a distance of one light-year?
Accelerating electric charges are the source of electromagnetic waves.
What is the source of electromagnetic waves?
Infrared light has a lower frequency than visible light, and visible light has a lower frequency than ultraviolet light.
How do the frequencies of infrared, visible, and ultraviolet light compare?
Each type of atom, molecule, and light vibrate with its own frequency.
Different bells and tuning forks have their own natural vibrations, and emit their own tones when struck. How is this analogous to atoms, molecules, and light?
The light emerges at its initial speed.
Light incident upon a pane of glass slows down in passing through the glass. Does it emerge at a slower speed or at its initial speed?
Glass will not be transparent to frequencies of light that match its natural frequency
Will glass be transparent to frequencies of light that match its own natural frequencies?
In a vacuum there are no particles for the light to collide with so it travels faster than it would in the atmosphere.
Why would you expect the speed of light to be slightly less in the atmosphere than in a vacuum?
The energy of these vibrations will tend to be absorbed and turned into heat.
When light encounters a material, it can build up vibrations in the electrons of certain atoms than may be intense enough to last over a long period of time. Will the energy of these vibrations tend to be absorbed and turned into heat, or absorbed and reemitted as light?
Transparent materials absorb light and then reemit it, opaque materials absorb light without reemission.
What determines whether or not a material is transparent or opaque?
The light from the sun is evidence that light can travel through a vacuum.
What evidence can you cite to support the idea that light can travel through a vacuum?
Because ultraviolet light vibrates at the natural frequency of glass, it does not pass through glass.
You can get a sunburn on a sunny day and on an overcast say. But you cannot get a sunburn if you are behind glass. Explain.
Light slows down when passing through glass, so its average speed would be less than its speed if it just traveled through the air. However, the light does not stop as the person did.
Pretend a person can walk only at a certain pace, no faster, no slower. If you time her uninterrupted walk across a room of known length, you can calculate her walking speed. If however, she stops momentarily along the way, the extra time spent in her brief interactions gives an average speed across the room that is less than her walking speed. How is this like light passing through glass? How is it not?
Blue light takes longer to pass through glass than red light.
Short wavelengths of visible light interact more frequently with the atoms in glass than do longer wavelengths. Which do you suppose takes the longer time to get through glass, red light or blue light?
both planes cast umbras and penumbras. The penumbra of the high flying plane fills the umbra
Why does a high-flying plane cast little or no shadow on the ground, while a low flying plane casts a sharp shadow?
50 % of light is transmitted when the glasses are aligned, but 0% of light will be transmitted when the glasses are crossed at right angles.
What percentage of light would be transmitted by two ideal polarizing filters, one atop the other, with their axes aligned? With their axes crossed at right angles?
The order of the colors in the color spectrum is red, orange, yellow, green, blue, and violet.
List the order of colors in the color spectrum.
Black and white are not real colors in the sense that red and green are. White is a combination of all colors, and black is the absence of light. Objects appear white when they reflect all visible light frequencies, and black when they absorb all visible light frequencies.
Are black and white real colors, in the sense that red and green are? Explain.
Light is emitted by the vibrating electrons of atoms.
A vibrating tuning fork emits a sound. What is emitted by the vibrating electrons of an atom?
Light of a certain frequency that encounters atoms of the same resonant frequency is absorbed.
What happens to light of a certain frequency that encounters atoms of the same resonant frequency?
An incandescent lamp emits light of all the visible frequencies, but is richer toward the lower frequencies, enhancing the blues. A fluorescent lamp is richer in the higher frequencies, so blues are enhanced when illuminated with fluorescent lamps.
Why does the color of an object look different under a fluorescent lamp from the way it looks under an incandescent lamp?
a. A transparent red object transmits red light.
b. It absorbs all other frequencies.
b. It absorbs all other frequencies.
a. What color(s) of light does a transparent red object transmit?
b. What color(s) does it absorb?
The name of the color produced by a mixture of blue and green light is cyan.
What is the name of the color produced by a mixture of green and blue light?
Complimentary colors are colors that produce white when added together.
What are complimentary colors?
Yellow is the compliment of blue.
What color is the compliment of blue?
Incident rays and reflected rays make equal angles with a line perpendicular to the surface, called the normal.
What is meant by the normal to a surface?
The law of reflection states that angle of incidence = angle of Reflection.
What is the law of reflection?
When you view your image in a plane mirror, your image is as far behind the mirror as you are in front of the mirror.
When you view your image in a plane mirror, how far behind the mirror is your image compared with your distance in front of the mirror?
In a diffuse reflection, although the reflection of each single ray obeys the law of reflection, the many different angles that incident light rays encounter cause reflection in many directions.
Does the law of reflection hold for diffuse reflection? Explain.
If light had the same speed in air and in water, it would not be refracted in passing from air into water.
If light had the same speed in air and in water, would light be refracted in passing from air to water?
If you can see the face of a friend who is underwater, she can also see you.
If you can see the face of a friend who is underwater, can she also see you?
On hot days there may be a layer of very hot air in contact with the ground. Since molecules in hot air are farther apart, light travels faster through it than through the cooler air above. The speeding up of the part of the wave nearest the ground produces a gradual bending of light rays. This can produce an image that appears upside down to an observer to an observer, just as if it were reflected from a surface of water. But the light is not reflected; it is refracted.
Is a mirage a result of refraction or reflection? Explain.
The conditions for seeing a rainbow are that the sun be shining in one part of the sky and that water droplets in a cloud or in falling rain be in the opposite part of the sky.
What conditions are necessary for viewing a rainbow in the sky?
A raindrop is similar to a prism in the way that it disperses light in to its spectral colors.
How is a raindrop similar to a prism?
The critical angle is the angle required for light to experience total internal reflection rather than refraction.
What is the critical angle in terms of refraction and total internal reflection?
Optical fibers are sometimes called light pipes because they pipe light from one place to another.
Why are optical fibers often called light pipes?
The reflection from a dry road is diffuse due to irregularities in the road, so light bounces in all different directions. The reflection from a wet road is mirrored, so the light bounces back into the driver’s eyes, making it difficult to see ahead of them.
Contrast the types of reflection from a rough road and from the smooth surface of a wet road to explain why it is difficult for a motorist to see the roadway ahead when driving on a rainy night.
1.1 s
A hypnotist swings his watch from a 0.30 m long chain. What is the period of the swing?
sound
Which of the following does not travel as a transverse wave?
out of phase
Standing waves are produced by the interference of a reflected wave and an incident wave that are_________________.
natural frequency
Rubbing a finger around the rim of a crystal glass will produce a specific sound characteristic of the crystal. This is said to be the crystal’s
high pressure
In a sound wave, a compression is an area of _____________ .
vacuum
Sound waves cannot travel through which of the following substances:
When frequency increases, pitch increases.
How are frequency and pitch related?
radio waves
Which of the following has the least energy?
The combined beat frequency is 3 Hz.
If two notes are played, one at 250 Hz and the other at 253 Hz, what is the combined beat frequency?
The Doppler effect is an observed shift in frequency received due to motion of a vibrating source toward or away from a receiver. When a car horn is being sounded, the change in pitch can be heard as the distance from the car to the observer changes. The pitch increases as the car gets closer and decreases as it gets farther away. The observer notices the effect. The person in the car does not notice the effect.
Explain what the Doppler Effect is and how it can be heard when a car horn is being sounded. Who notices the effect? Who does not notice the effect?
The range of electromagnetic waves extending from radio waves to gamma rays
electromagnetic spectrum
A wave that is partly electric and partly magnetic and carries energy. Emitted by vibrating electric charges.
electromagnetic wave
electromagnetic waves of frequencies lower than the red of visible light
infrared
the distance light travels through a vacuum in one year
light-year
term applied to materials that absorb light without reemission, and consequently do not allow light through them
opaque
a partial shadow that appears where light from part of the source is blocked and light from another part of the source is not blocked
penumbra
the aligning of vibrations in a transverse wave
polarization
a thin beam of light
ray
electromagnetic waves with frequencies higher than those of violet light.
ultraviolet
the darker part of the shadow where all light is blocked
umbra
pattern of distinct lines of color, corresponding to particular wavelengths, that are seen in a spectroscope when a hot gas is viewed.
line spectrum
a material that selectively absorbs colored light
pigment
an instrument used to separate the light from a hot gas or other light source into its constituent frequencies
spectroscope
It takes 1.5 seconds to make a complete back-and-forth vibration. This 1.5-second pendulum is longer in length than a 1-second pendulum.
Suppose that a pendulum has a period of 1.5 seconds. How long does it take to make a complete back-and-forth vibration? Is this 1.5 second period pendulum longer or shorter in length than a 1-second period pendulum?
The period of a wave or a vibration is the time it takes for one complete back and forth vibration. The frequency of a wave or a vibration specifies the number of back-and-forth vibrations it makes in a given time. If the frequency of a vibrating object is known, its period can be calculates, and vice versa. As you can see below, frequency and period are inverses of each other:
Frequency = 1/period Period = 1/ Frequency
Distinguish between the period and the frequency of a vibration or a wave. How do they relate to one another?
The speed of a wave is equal to its wavelength multiplied by its frequency.
How does the speed of a wave relate to its wavelength and frequency?
As the frequency of a sound is increased, the wavelength decreases. For example, during a concert, you do not hear the high notes in a chord before you hear the low ones; the sounds of all instruments reach you at the same time. Wavelength and frequency vary inversely to produce the same wave speed for all sounds.
As the frequency of sound is increased, does the wavelength increase or decrease? Give an example.
Standing waves are the result of interference. When two waves of equal amplitudes pass each other in opposite directions, the waves are always out of phase at the nodes. The nodes are stable regions of destructive interference.
What causes a standing wave?
When a wave source moves toward a receiver, the receiver encounters an increase in wave frequency, but not in wave speed.
When a wave source moves toward a receiver, does the receiver encounter an increase in wave frequency, wave speed, or both?
To keep up with the waves it is producing, the bug must swim as fast as the waves it is producing. To produce a bow wave, the boat would need to be moving faster than the waves that it is producing.
How fast must a bug swim to keep up with the waves it is producing? How fast must a boat move to produce a bow wave?
No, a shock wave and its resulting sonic boom are swept continuously behind an aircraft traveling faster than sound. The aircraft that has generated this shockwave may have broken through the sound barrier hours ago.
If you encounter a sonic boom, is that evidence that an aircraft of some sort exceeded the speed of sound moments ago to become supersonic? Defend your answer.
Violet light has the greater frequency.
Red light has a longer wavelength than violet light. Which has the greater frequency?
If you triple the frequency of a vibrating object, its period will decrease by a factor of 3.
If you triple the frequency of a vibrating object, what will happen to its period?
If a wave vibrates up and down twice each second and travels a distance of 20 m each second, its frequency is 2 Hz, and its wave speed is 20 m/s. This question is better answered by carefully reading the question rather than searching for a formula because all of the information needed is given in the question.
If a wave vibrates up and down twice each second and travels a distance of 20 m each second, what is its frequency? Its wave speed?
No, the Doppler effect is the apparent change in frequency and pitch of a wave due to motion of the source. This question is a test of reading comprehension as well as a test of physics knowledge because it requires you to know the difference between frequency and speed and the definition of the Doppler effect.
Would it be correct to say that the Doppler effect is the apparent change in the speed of a wave due to motion of the source?
A high-pitched sound has a high vibration frequency, while a low-pitched sound has a low vibration frequency.
Hoe does pitch relate to frequency?
Sound cannot travel in a vacuum. The transmission of sound requires a medium. If there is nothing to compress and expand, there can be no sound.
Light can travel through a vacuum, as is evidenced when you see the sun or the moon. Can sound travel through a vacuum also? Explain why or why not.
a. In dry air at room temperature, sound travels at about 340 m/s.
b. For each degree increase in air temperature above 0 degrees C, the speed of sound in air decreases by 60 m/s.
b. For each degree increase in air temperature above 0 degrees C, the speed of sound in air decreases by 60 m/s.
a. How fast does sound travel in dry air at room temperature?
b. How does air temperature affect the speed of sound?
Sound travels faster in solids than in liquids and gases because solids have higher elasticity than liquids and gases.
Why does sound travel faster in solids and liquids than in gases?
Sound is louder when a vibrating source is held to a sounding board because the sounding board is forced to vibrate and its larger surface area sets more air in motion.
Why is a sound louder when a vibrating source is held to a sounding board?
Resonance occurs when the frequency of a forced vibration on an object matches the object’s natural frequency and an increase in amplitude occurs.
What is the relationship between forced vibration and resonance?
In order for something to resonate, it needs a force to pull it back to its starting position and enough energy to keep it vibrating. Tissue paper is too limp to resonate.
Why can a tuning fork or bell be set into resonance, while a tissue paper cannot?
The interference of two sound sources of slightly different frequencies produces beats.
How does interference of sound relate to beats?
We hear the bat hitting the ball before after we actually see the hit because light travels faster than sound.
When watching a baseball game, we often hear the bat hitting the ball after we actually see the hit. Why?
First of all, sound cannot travel through space, and second, the sound made by a distant explosion would take longer to reach an observer than the light of the explosion, so the sound would not occur at the same time that you see the explosion.
What two physics mistakes occur in a science fiction movie when you see and hear at the same time a distant explosion in outer space?
When a sound wave propagates past a point in the air, the air pressure of this point decreases.
When a sound wave propagates past a point in the air, what are the changes that occur in the pressure of air at this point?
A close whisper is 100 times more intense than the threshold of breathing. A close whisper is 10 times more intense that normal breathing.
Hoe much more intense is (a) a close whisper than the threshold of hearing? (b) a close whisper than normal breathing?
Two, four, and six Hz are the possible beat frequencies for pairs of these forks sounded together.
Suppose three tuning forks of frequencies 260 Hz, 262 Hz, and 266 Hz are available. What beat frequencies are possible for pairs of these forks sounded together?
She should further tighten the string.
Suppose a piano tuner hears 2 beats per second when listening to the combined sound from her tuning fork and the piano note being tuned. After slightly tightening the string, she hears 1 beat per second. Should she loosen or should she further tighten the string?
76 heartbeats/60 seconds = 1 heartbeat/ 0.79 seconds
frequency = 1/period = 1/0.79 s = 1.27
The period is 0.79 seconds and the frequency is 1.27 Hz.
A nurse counts 76 hearbeats in one minute. What are the period and frequency of the heart’s oscillations?
wave speed = wavelength x frequency = 0.15 m x 2 Hz = 0.3 ms/s
Calculate the speed of waves in a puddle that are 0.15 m apart and made by tapping the water surface twice each second.
period= s/wave = 30/10 = 3s
frequency = wave/s = 10/30 = 0.3 Hz
wavelength = 5m
wave speed = wavelength x frequency = 5m x 0.3s = 1.5 m/s
frequency = wave/s = 10/30 = 0.3 Hz
wavelength = 5m
wave speed = wavelength x frequency = 5m x 0.3s = 1.5 m/s
While watching ocean waves at the dock of the bay, Otis notices that 10 waves pass beneath him in 30 seconds. He also notices that the crests of successive waves exactly coincide with the posts that are 5 meters apart. What are the period, frequency, wavelength, and speed of the ocean waves?
V = λƒ
340 m/s = (20Hz)λ
λ = 17 m
340 m/s = (20Hz)λ
λ = 17 m
340 m/s = (20000Hz)λ
λ = 0.017 m
Sound waves travel at approximately 340 m/s. What is the wavelength of a sound with a frequency of 20 Hz? What is the the wavelength of a sound with a frequency of 20 kHz?
V = d/t
1530 m/s = d/4
1530 m/s = d/4
6120 m = d
An oceanic depth-sounding vessel surveys the ocean bottom with ultrasonic sound that travels 1530 m/s in seawater. Find the depth of the water if the time delay of the echo to the ocean floor and back is 8 seconds.
the distance from the midpoint to the crest of the wave
amplitude
a wiggle in time
vibration
a wiggle in space
wave
time it takes for one complete back and forth vibration
period
the distance between successive identical parts of the wave
wavelength
the medium moves at right angles to the direction in which the wave travels
ex. electromagnetic waves, such as light and radio waves
ex. electromagnetic waves, such as light and radio waves
transverse wave
the medium moves back and forth parallel to the direction in which the wave travels
ex. sound waves
ex. sound waves
longitudinal wave
crest overlaps crest or a trough overlaps a trough
constructive interference
crest overlaps a trough
destructive interference
a throbbing variation in the loudness of sound caused by interference when two tones of slightly different frequencies are sounded together
beats
a pulse of compressed air; opposite of rarefaction
compression
the vibration of an object that is made to vibrate by another vibrating object that is nearby
forced vibration
term applied to sound pitch too low to be heard by the human ear, that is, below 20 Hz
infrasonic
a frequency at which an elastic object, once energized, will vibrate
natural frequency
term that refers to how high or low sound frequencies appear to be
pitch
a disturbance in air in which pressure is lowered; opposite of compression
rarefaction
a phenomenon that occurs when the frequency of forced vibrations on an object matches the object’s natural frequency, and a dramatic increase in amplitude results
resonance
term applied to sound frequencies above 20,000 Hz, the normal upper limit of human hearing
ultrasonic
