Physics : Semiconductor Electronics: Materials, Devices and Simple Circuits

When LED is forward biased, then

• electrons from the n-type material cross the p-n junction and recombine with holes in the p-type material

• electrons and holes neutralise each other

• at junction electrons and holes neutralize each other

• None of the above

The electrical conductivity of semiconductor increases, when electromagnetic radiation of a wavelength shorter than 24800 Å is incident on it. The bandgap for the semiconductor is

• 0.9 eV

• 0.7 eV

• 0.5 eV

• 1.1 eV

Identify the operation performed by the circuit given below

• NOT

• AND

• OR

• NAND

In a transistor, the collector current is always less than the emitter current because

• collector side is reverse biased and the emitter side is forward biased

• a few electrons are lost in the base and only remaining ones reach the collector

• collector being reverse biased attracts less electron

• collector side is forward biased and emitter side is reverse biased

To a germanium crystal, an equal number of aluminium and indium atoms are added. Then

• it remains an intrinsic semiconductor

• it becomes a n-type semiconductor

• it becomes a p-type semiconductor

• it becomes an insulator

In a reverse-biased diode when the applied voltage changes by 1 V, the current is found to change by 0.5 µA. The reverse bias resistance of the diode is

• 2 × 10⁵ Ω

• 2 × 10⁶ Ω

• 200 Ω

• 2 Ω

Forward bias characteristics of a p-n junction diode are used in which of the following devices?

• Transistor

• Tank circuit

• Rectifier

• All of these

The energy gap between the conduction band and valence band is of the order of 0.07 eV. It is a/an

• insulator

• conductor

• semiconductor

• alloy

An oscillator is basically an amplifier with gain

• less than unity

• more than unity

• zero

• 0.5

A triode valve has an amplification factor of 20 and its plate is given a potential of 300 V. The grid voltage to reduce the plate current to zero, is

• 25 V

• 12 V

• 10 V