Physics Test 220

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Physics Test 220

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Weekly Quiz Competition

Question 1
4 / -1

In a series LCR circuit, R = 200Ω and the voltage and frequency of the main supply are 220 V and 50 Hz, respectively. On taking out the capacitance from the circuit, the current lags behind the voltage by 30°. On taking out the inductor from the circuit, the current leads the voltage by 30°. The power dissipated in the LCR circuit is

A
242 W

B
305 W

C
210 W

D
0 W

Solution
Question 2
4 / -1

Two equally charged identical metal spheres A and B repel each other with a force of 2.0 ×10^–5 N. Another identical uncharged sphere C is made to touch A and then placed at the midpoint between A and B. What is the net force on C?

A
6 × 10^-6 N along BC

B
5 × 10^-4 N along BC

C
2 × 10^-5 N along BC

D
3 × 10^-2 N along BC

Solution
Question 3
4 / -1

What is the use of ball bearings between hubs and the axle of ceiling fans and bicycles?

A
Converts rolling friction into sliding friction

B
Converts static friction into kinetic friction

C
Converts sliding friction into rolling friction

D
Converts static friction into rolling friction

Solution

Since the rolling friction is smaller than the sliding friction, thus, sliding friction is converted into rolling friction with the use of ball bearings.
Question 4
4 / -1

A particle of mass 0.3 kg is subjected to a force F = -kx, with k = 15 N/m. What will be its initial acceleration if it is released from a point 20 cm away from the origin?

A
5 m/s²

B
10 m/s²

C
3 m/s²

D
15 m/s²

Solution

Initial acceleration is overcome by retarding force.

Or, m × (acceleration, a) = 3

Or, a = 3/m = 3/0.3 = 10 ms^-2
Question 5
4 / -1

A projectile is fired at an angle 60° with some velocity u. If the angle is changed infinitesimally, let the corresponding fractional changes in the range and the time of flight be x and y, respectively, then find the value of y.

A

B

C
-2x

D
2x

Solution
Question 6
4 / -1

The velocity of a particle is v = v₀ + gt + ft². If its position is x = 0 at t = 0, then its displacement after unit time (t = 1) is

A
v₀ + g/2 + f

B
v₀ + 2g + 3f

C
v₀ + g/2 + f/3

D
v₀ + g + f

Solution
Question 7
4 / -1

A giant telescope in an observatory has an objective of focal length 19 m and an eye-piece of focal length 1.0 cm. In normal adjustment, the telescope is used to view the moon. What is the diameter of the image of the moon formed by the objective? (The diameter of the moon is 3.5 × 10⁶ m and the radius of the lunar orbit around the Earth is 3.8 × 10⁸ m)

A
10 cm

B
12.5 cm

C
15 cm

D
17.5 cm

Solution

Since u >> f₀, v = f₀ = 19 m.

Now, u = -3.8 × 10⁸ m

Therefore, magnification produced by the objective,

∴ Diameter of the image of the moon = 3.5 × 10⁶ 0.5 × 10^-7 = 0.175 m = 17.5 cm

Hence, the correct choice is (4).
Question 8
4 / -1

Carbon, silicon and germanium have four valence electrons each. At room temperature, which of the following statements is the most appropriate?

A
The number of free electrons for conduction is significant only in Si and Ge, but small in C.

B
The number of free conduction electrons is significant in C, but small in Si ad Ge.

C
The number of free conduction electrons is negligibly small in all three.

D
The number of free electrons for conduction is significant in all three.

Solution

C, Si and Ge have the same lattice structure and their valence electrons are 4. For C, these electrons are in the second orbit, for Si, they are in the third orbit, and for germanium, it is in the fourth orbit. In solid state, higher the orbit, greater the possibility of overlapping of energy bands. Ionisation energies are also less, therefore Ge has more conductivity as compared to Si. Both are semiconductors. Carbon is an insulator.
Question 9
4 / -1

A metallic container is completely filled with a liquid. The coefficient of linear expansion of the metal is 2.0 × 10^-6per °C and the coefficient of cubical expansion of the liquid is 6.0 × 10^-6 per °C. On heating the vessel,

A
the liquid will overflow

B
the level of the liquid will fall

C
the level of the liquid will remain unchanged

D
the level of liquid will rise or fall depending on the nature of the metal and of the liquid

Solution

The coefficient of cubical expansion of the vessel = 3α = 3 × 2.0 × 10^-6 = 6.0 × 10^-6 per °C.

Hence, 3α = γ

Hence, cubical expansion of the vessel is equal to the cubical expansion of the liquid. Hence, the increase in the volume of the liquid is equal to the increase in the volume of the vessel. Thus, the correct choice is (3).
Question 10
4 / -1

Directions: In this question, two statements are given, numbered 1 and 2. Read both the statements carefully and choose the correct option accordingly.

Statement-1: The temperature dependence of resistance is usually given as R = R₀(1 + αΔt). The resistance of a wire changes from 100 Ω to 150 Ω when its temperature is increased from 27°C to 227°C. This implies that α = 2.7 10^-3/°C.

Statement-2: R = R₀(1 + αΔt) is valid only when the change in the temperature ΔT is small and ΔR = (R - R₀) << R₀.

A
Statement-1 is true, but statement-2 is false.

B
Both statements 1 and 2 are true, and statement-2 is the correct explanation for statement-1.

C
Both statements 1 and 2 are true, but statement-2 is not the correct explanation for statement-1.

D
Statement-1 is false, but statement-2 is true.

Solution

The resistance of a wire changes from 100Ω to 150Ω when the temperature is increased from 27°C to 227°C.

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