# MS Solid State Physics Past Paper 2020 Punjab University The MS Solid State Physics Past Paper 2020 Punjab University is a document that contains the questions and answers of the Master of Science (MS) Solid State Physics examination held in 2020 by the University of the Punjab Lahore Pakistan.

## Suppose A = BC, where A has the dimension of ​$$\mathrm{\frac{L}{M}}$$​ and C has the dimension of ​$$\mathrm{\frac{L}{T}}$$​. Then B has the dimension of

1. $$\mathrm{\frac{T}{M}}$$
2. $$\mathrm{\frac{L^{2}}{TM}}$$
3. $$\mathrm{\frac{TM}{L^{2}}}$$
4. $$\mathrm{\frac{M}{L^{2}T}}$$

Correct Option: (A)

$\mathrm{A = BC}$

$\mathrm{B = \frac{A}{C}}$

$\mathrm{B = \frac{L/M}{L/T}}$

$\mathrm{B = \frac{T}{M}}$

## Why do raindrops fall with constant speed during the later stages of their descent?

1. All the drops fall from the same height
2. Air resistance just balances the force of gravity
3. The gravitational force is the same for all drops
4. The force of gravity is negligible for objects as small as raindrops

Correct Option: (B)

Raindrops fall with constant speed during the later stages of their descent because the force of air resistance balances the force of gravity.

## Which of the following bodies has the largest kinetic energy

1. Mass 3M and speed V
2. Mass M and speed 4V
3. Mass 3M and speed 2V
4. Mass 2M and speed 3V

Correct Option: (D)

The kinetic energy (KE) of an object is given by the formula

$\mathrm{KE = \frac{1}{2}mv^{2}}$

$\mathrm{KE = \frac{1}{2}(3M)V^{2} = 1.5MV^{2}}$

$\mathrm{KE = \frac{1}{2}(M)(4V)^{2} = 8MV^{2}}$

$\mathrm{KE = \frac{1}{2}(3M)(2V)^{2} = 6MV^{2}}$

$\mathrm{KE = \frac{1}{2}(2M)(3V)^{2} = 9MV^{2}}$

Out of these options, mass 2M and speed 3V have the largest kinetic energy.

## When the temperature of a copper penny is increased by 100oC and its diameter increases by 0.17%. The area of one of its faces increases by

1. 0.17%
2. 0.51%
3. 0.34%
4. 0.085%

Correct Option: (C)

$\mathrm{A = \pi r^{2}}$

$\mathrm{A = \pi \left( \frac{d}{2} \right)^{2} = \frac{\pi d^{2}}{4}}$

$\mathrm{\Delta A = \frac{\pi}{4} \ 2d \Delta d}$

$\mathrm{\frac{\Delta A}{A} = \frac{\pi}{4} \ 2d \Delta d \ ÷ \ \frac{\pi d^{2}}{4}}$

$\mathrm{\frac{\Delta A}{A} = 2\times \frac{\Delta d}{d}}$

$\mathrm{\frac{\Delta A}{A} = 2\times 0.17 \%}$

$\mathrm{\frac{\Delta A}{A} = 0.34 \%}$

## Heat has the same units as

1. Work
2. Power
3. Specific heat
4. Temperature

Correct Option: (A)

Heat has the same units as work. Both heat and work are measured in joules (J).

## The torque exerted by an electric field on a dipole is

1. Parallel to both the field and the dipole moment
2. Perpendicular to both the field and the dipole moment
3. Parallel to the dipole moment and perpendicular to the field
4. Parallel to the field and perpendicular to the dipole moment

Correct Option: (B)

The torque exerted by an electric field on a dipole can be mathematically expressed as

$\mathrm{\overrightarrow{\tau} = \overrightarrow{p} \times \overrightarrow{E}}$

The vector product of two vectors is perpendicular to both vectors. So the torque is perpendicular to both the electric field and the dipole moment.

## Lenz’s law is the consequence of the law of conservation of

1. Energy
2. Torque
3. Current
4. Momentum

Correct Option: (A)

Lenz’s law is the consequence of the law of conservation of energy.

## Each plate of a capacitor stores a charge of magnitude 1 mC when a 100 V potential difference is applied. The capacitance is

1. 5 µF
2. 10 µF
3. 50 µF
4. 100 µF

Correct Option: (B)

The capacitance of a capacitor is given as

$\mathrm{C = \frac{Q}{V}}$

$\mathrm{C = \frac{1 \times 10^{-3}}{100}}$

$\mathrm{C = 10^{-5} \ F}$

$\mathrm{C = 10 \ \mu F}$

## The units of magnetic dipole moment are

1. ampere-meter
2. ampere-meter2
3. ampere-meter-1
4. ampere-meter-2

Correct Option: (B)

A magnetic dipole moment is a vector quantity that describes the strength and orientation of a magnetic field.

It is defined as the product of the current flowing through a loop of wire and the area of the loop.

$\mathrm{\mu = I A}$

Its SI unit is A-m2.

## The most commonly used material in semiconductor devices is

1. Silicon
2. Graphene
3. Germanium
4. Gallium nitride