The anode voltage of a photocell is kept fixed. The wavelength λ of the light falling on the cathode is gradually changed. The plate current I of the photocell varies as follows

If the lattice constant of this semiconductor is decreased, then which of the following is correct?

• All E_c, E_g, E_v decrease

• All E_c, E_g, E_v increase

• E_c, and E_v increase but E_g decreases

• E_c, and E_v increase but E_g decreases

In the following, which one of the diodes is reverse biased?

The circuit has two oppositely connect ideal diodes in parallel. What is the current following in the circuit?

• 1.33 A

• 1.71 A

• 2.00 A

• 2.00 A

The electrical conductivity of a semiconductor increases when electromagnetic radiation of wavelength shorter than 2480 nm is incident on it. The band gap in (eV) for the semiconductor is

• 1.1 eV

• 2.5 eV

• 0.5 eV

• 0.5 eV

In a common base amplifier, the phase difference between the input signal voltage and output voltage is

• π/4 

• π

• 0

• 0

27.

The thermistors are usually made of

• metals with low temperature coefficient of resistivity

• metals with high temperature coefficient of resistivity

• metal oxides with high temperature coefficient of resistivity ‘

• metal oxides with high temperature coefficient of resistivity ‘

When npn transistor is used as amplifier

• electrons move from base to collector

• holes move from emitter to base

• electrons move from collector to base

• electrons move from collector to base

For a transistor amplifier in common emitter configuration having load impedance of 1 kΩ (h_fe = 50 and h_oe = 25) the current gain is

• -5.2

• -15.7

• -24.8

• -24.8

A piece of copper and another of germanium are cooled from room temperature to 77 K, the resistance of

• each of them increases

• each of them decreases

• copper decreases and germanium increases

• copper decreases and germanium increases