# GOMCQS – Prepare MCQs for all Competitive Exams

## When a forward bias is applied to a p-n junction the concentration of electrons

1. Increases slightly
2. Decreases slightly
3. Increases dramatically
4. Decreases dramatically

Correct Option: (A)

When a forward bias is applied to a p-n junction the concentration of electrons increases slightly.

## Which of the following pieces of experimental evidence contributed to the development of quantum mechanics

1. Hall effect
2. Diffraction
3. Doppler effect
4. Photoelectric effect

Correct Option: (D)

The photoelectric effect is the only experimental evidence from the options that contributed to quantum mechanics because it shows light has particle-like properties.

## The wave represents the motion of an electron in

1. Zero potential
2. Weak potential
3. Periodic potential
4. Constant potential

Correct Option: (C)

The periodic potential is a potential that repeats itself at regular intervals.

The wave function of an electron in a periodic potential is called a Bloch wave.

Bloch waves are solutions to the Schrodinger equation for a periodic potential.

## In Bragg equation (2dSin​$$\theta$$​ = n​$$\lambda$$​) then n represents

1. Quantum number
3. The number of moles
4. The order of reflection

Correct Option: (D)

In the Bragg equation n represents the order of reflection.

The order of reflection is the number of times the X-ray beam is reflected off of the crystal planes.

The higher the order of reflection the further apart the crystal planes are.

## The electrical conductivity of a semiconductor

1. Decreases with an increase in temperature
2. Increases with increase in temperature
3. Remains constant on heating
4. None of the above

Correct Option: (B)

The electrical conductivity of a semiconductor increases with increases in temperature.

This is because the number of charge carriers in a semiconductor increases as the temperature increases this is because the thermal energy of the atoms is increased which allows more electrons to break free from the valence band and enter the conduction band.

## A current-carrying conductor would move when placed in a magnetic field was discovered by

1. George Ohm
2. Andre Ampere