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 × 102m
N.B 600KHz Frequency = 600 × 103Hz
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 = \(\frac{1}{2}\) cv2
= \(\frac{1}{2}\) × (8 × 10− 6) × 102
= 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