**21**.

**A.**80µF**B.**6.0µF**C.**4.0µF**D.**2.0µF

**Correct Option: Answer is D**

For capacitance i n parallel, 2µF and 2µF are in parallel,

their equivalence is 2µF and 2µF = 4µF

The 4µF generated is now in series with the remaining 4µF.

The net capacitance for series connection is

\(\frac{1}{C}\) = \(\frac{1}{4}\) + \(\frac{1}{4}\) = 1 + \(\frac{1}{4}\) = \(\frac{2}{4}\)

C = \(\frac{4}{2}\)

= 2µF

**22. **The instrument used to measure the pressure of a gas is

**A.**barometer**B.**thermometer**C.**hygrometer**D.**manometer

**Correct Option: Answer is D**

Barometer is used to measure atmosphere pressure

Thermometer is used to measure temperature

Hygrometer is used to measure relative density of a liquid

Manometer is used to measure the pressure of a gas

**23. **A radio station broadcast at a frequency of 600KHZ. If the speed of light in air is 3 × 108ms\(^{−1}\). Calculate the wavelength of the radio wave

**A.**2.20 × 10\(^3\)m**B.**5.0 × 10\(^2\)m**C.**5.0 × 10\(^5\)m**D.**11.8 × 10\(^{11}\)m

**Correct Option: Answer is B**

V = fλ

λ = \(\frac{v}{f}\)

= \(\frac{3 \times 10^8}{600 \times 10^3}\) = 500m

= 5 × 10^{2}m

N.B 600KHz Frequency = 600 × 10^{3}Hz

**24. **Which of the following is a scalar quantity?

**A.**Tension**B.**Weight**C.**Impulse**D.**Mass

**Correct Option: Answer is D**

Scalar quantity is a quantity with only magnitude, it has no direction

Tension, weight, impulse are vector quantities because they have direction. Mass is the only scalar quantity there

**25. **Determine the focal length of a thin converging lens if the power is 5.0 dioptres

**A.**0.1 m**B.**0.2 m**C.**2.0 m**D.**2.5 m

**Correct Option: Answer is B**

Power of a lens = 1/f

f = focal length

f = 1 / p

= 1 / 5

= 0.2m

**26. **A string of length 5cm is extended by 0.04m when a load of 0.8kg is suspended at the end. How far will it extend if a force of 16N is applied? [g = 10ms−2]

**A.**0.04m**B.**0.12m**C.**0.01m**D.**0.08m

**Correct Option: Answer is D**

From Hoke’s Law, F = ke, K = Constant of Force

For he first case, Force = mg,

= 0.8 × 10 = 8N

∴ 8 = k × 0.04

k = \(\frac{8}{0.04}\)

= \(\frac{200N}{m}\)

Since K is constant

For the second case, F = ke

F = 200 × e

∴ e = \(\frac{F}{200}\)

= \(\frac{16}{200}\)

= 0.08m

**27. **How can energy loss be minimized through Eddy-current?

**A.**By using high resistance wire**B.**By using insulated soft iron wires**C.**By using low resistance wires**D.**Bu using turns of wires

**Correct Option: Answer is A**

Eddy currents are produced by the varying flux cathode, the iron core of an equipment thus reducing efficiency due to power consumption. It can be reduced by laminating the core by breaking up the path of eddy current or by increasing the resistance of the core

Usage of insulated soft iron wire is to reduce hysteresis loss

Usage of low resistance wire (thick wire) is to reduce I2R loss

Usage of thick wire is to reduce leakage heat loss due to leakage of magnetic flux

Thus the correct answer is to use high resistance wire or thin wire

**28.**

**A.**4.0 x 10−2J**B.**4.0 x 10−4J**C.**8.0 x 10−4J**D.**8.0 x 10−2J

**Correct Option: Answer is B**

c = 8µF, v = 10v

Energy stored = \(\frac{1}{2}\) cv^{2}

= \(\frac{1}{2}\) × (8 × 10− 6) × 10^{2}

= 4 × 10\(^{-4}\)

**29. **A constant force of 5N acts for a 5 seconds on a mass of 5kg initially at rest. Calculate the final momentum

**A.**125kgms−1**B.**25kgms−1**C.**15kgms−1**D.**0kgms−1

**Correct Option: Answer is B**

Impulse = momentum

Impulse = Force (f) × time (t)

Momentum = mass (m) × velocity (v)

∴ Ft = Final momentum – initial momentum

FT = mv – mu

Since it is initially at rest u = 0

∴ 5 × 5 = mv − m(0)

25 = mv

∴ Final momentum = 25kgms−1

**30. **

I. Refraction

II. Interference

III. Diffraction

Which of the above properties are common to all waves?

**A.**II and III only**B.**I, II and III**C.**I and II only**D.**I and III only

**Correct Option: Answer is B**

Refraction, Interference and diffraction are all properties of waves