One terminal being known as anode and other known as cathode. A diode should work like a switch. When its anode made positive with respect to its cathode, the diode should act like a closed switch and when its anode made negative with respect to its cathode, acts like an open switch. When a d. C. Voltage is applied to a device, the device is said to be biased. A p-n Junction can be biased in two ways- 1. If the positive terminal of the d. C. Supply is connected to p-region and negative terminal is connected to n-region (cathode), the diode is said to be forward biased. 2.
If the positive terminal of the d. C. Supply is connected to n-region and negative terminal is connected to p-region (cathode), the diode said to be reverse biased. – In forward bias the diode current increases rapidly as the potential across the diode is increased. The diode starts conducting only after a certain voltage known as threshold voltage. In the forward biased condition, majority charge carriers are responsible for conduction. The number of these charge carriers injected at the junction increases with the voltage and thus the current increases with voltage.
Under reverse bias condition minority charge carriers take part in the process of conduction. Here the leakage current flows in the circuit. This current is known as reverse saturation current. It increases rapidly in the initial stage due to an exponential decrease of diffusion current with increasing reverse voltage. – Junction diode in which the quantity of impurity doped is more than that of an ordinary diode. If a battery connected at the terminal of keener diode such that the positive terminal of the battery is connected to p and negative to N, it is said to be in forward bias. The holes of p- region are repelled by the positive electrode and more towards the Junction and electrons of N- region are repelled by the negative electrode and move towards the Junction.
Thus, electric conduction takes place at junction. A potential difference across the diode increases, the current in the circuit also increases. When the positive terminal of the battery is connected to N and negative connected to p, it is said to be in reverse bias. The holes of P region move away from the Junction and similarly the electron of N region move away from the junction. Thus no current flows in the reverse bias due to majority charge carriers. But the minority charge carriers of p region and holes of N region move towards the junction due to which a very feeble current flows.
On increasing the reverse voltage, a stage is reached when the current suddenly increases. This potential is called breakdown voltage. The reason is that when the reverse electric field at the Junction increases, the covalent bond break and a large number of charge carriers are reduced. This is called keener breakdown.
Connect the keener in reverse polarity of the supply in the given terminal. 2. Increase the supply voltage in steps and note the corresponding readings of the ammeter. 3. Ata particular voltage Vs. the current is maximum. Plot the graph between current and voltage. To determine the wavelength of violet and green light by using a diffraction grating.
Plane transmission grating, mercury lamp, reading lamp and reading lens. THEORY- when a parallel beam of monochromatic light of wavelength (from the collimator) is incident normally on a grating. By hugger’s principle each point of slit emits out secondary wavelets in all directions which interfere and get soused in the focal plane of a convex lens. The path difference between the diffracted waves at an angle B from the corresponding points of two consecutive slits is (e+d) sine . When this path difference is equal to integer multiple of wavelength principal maxima are obtained.
For n=O, we get zero order (or central) maxima and for n= , В±2…. .. We get first order, second order… Maxima respectively on either side of zero order maxima. Thus knowing the grating element (e+d) and the angle of diffraction B in a particular order n, the wavelength Roof light can be calculated. Now if white light is made incidence on a grating, in each order the value of B will be different, corresponding to different wavelengths present in the incident white light. Thus we get spectrum in each order.