Physics Test

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Physics Test - 2

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Question 1
1 / -0

An observer is moving towards a stationary source with 1/10 the speed of sound. The ratio of apparent frequency to real frequency is

A
11/10

B
10/9

C
(11/10)²

D
(9/10)²

Solution

Frequency as observed by the observer is
Question 2
1 / -0

The disc of a siren containing 60 holes rotates at a constant speed of 360 rpm. The emitted sound is in unison with a tuning fork of frequency

A
10 Hz

B
360 Hz

C
216 Hz

D
60 Hz

Solution

The number of holes in the disc determines the number of the waves produced on each rotation. The total number of waves emitted per second is the frequency,
Question 3
1 / -0

A police car horn emits sound at a frequency of 240 Hz when the car is at rest. If the speed of sound is 330 m/s, the frequency heard by an observer who is approaching the car at a speed of 11 m/s, is

A
248 Hz

B
244 Hz

C
240 Hz

D
230 Hz

Solution
Question 4
1 / -0

A point source emits sound equally in all directions in a non-absorbing medium. Two points P and Q are at distances of 2 m and 3 m, respectively, from the source. The ratio of intensities of the waves at P and Q is

A
9 : 4

B
2 : 3

C
3 : 2

D
4 : 9

Solution
Question 5
1 / -0

Consider a train was moving along negative \(x\) direction with speed \(50 \mathrm{~km} / \mathrm{hr}\) and a boy walking inside that train with speed \(2 \mathrm{~km} / \mathrm{hr}\) towards positive \({x}\) direction, in this case, what will be the relative velocity of the boy with respect to the train.

A
\(48 \mathrm{~km}\) towards positive \(x\) direction

B
\(48 \mathrm{~km}\) towards negative \(x\) direction

C
\(52 \mathrm{~km}\) towards positive \({x}\) direction

D
\(52 \mathrm{~km}\) towards negative \(x\) direction

Solution

Given that:

Velocity of train, \(v_{t}=-50 \mathrm{~km} / \mathrm{hr}\)

Velocity of Boy \({v}_{\mathrm{B}}=2 \mathrm{~km} / \mathrm{hr}\)

Now relative velocity of the boy with respect to train will be:

\(v_{\text {relative }}=v_{B}-v_{t}=2-(-50)=52 \mathrm{~km} / \mathrm{hr}\)

The speeds get added as both are directed in opposite directions.

This shows that the boy is moving toward positive \(x\) -direction with speed \(52 \mathrm{~km} / \mathrm{hr}\).
Question 6
1 / -0

In photoelectric effect, we assume that photon energy is proportional to its frequency and is completely absorbed by the electrons in metal. Then, the photoelectric current

A
decreases when the frequency of the incident photon increases

B
increases when the frequency of the incident photon increases

C
does not depend upon the photon freqeuncy but only on the intensity of the incident beam

D
depends both on the intensity and frequency of the incident beam

Solution

Photocurrent depends upon the rate of transmission of charges from one end to other. The number of charges released will depend only on number of electrons falling on the metal plates, given by intensity. Frequency increases only the kinetic energy of electrons.
Question 7
1 / -0

The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV and the stopping potential for a radiation incident on this surface is 5 V. The incident radiation lies in

A
ultraviolet region

B
infrared region

C
visible region

D
X-ray region

Solution
Question 8
1 / -0

A photoelectric cell is illuminated by a point source of light 1 m away. When the source is shifted to 2 m, then

A
each emitted electron carries half the initial energy

B
number of electrons emitted is a quarter of the initial number

C
each emitted electron carries one quarter of the initial energy

D
number of electrons emitted is half the initial number

Solution
Question 9
1 / -0

The figure shows variation of photocurrent with anode potential for a photosensitive surface for three different radiations. Let I_a, I_b and I_c be the intensities and _a, _b and _c be the frequencies for the curves a, b and c, respectively. Then,

A

B

C

D

Solution
Question 10
1 / -0

Sodium surface is illuminated by ultraviolet and visible radiations, successively and the stopping potential is determined. This stopping potential is

A
equal in both cases

B
more with ultraviolet light

C
more with visible light

D
varies randomly

Solution
Question 11
1 / -0

The bob of a simple pendulum is a spherical hollow ball filled with water. A plugged hole near the bottom of the oscillating bob gets suddenly unplugged. During observation, till water is coming out, the time period of oscillation would

A
first increase and then decrease to the original value

B
first decrease and then increase to the original value

C
remain unchanged

D
increase towards a saturation value

Solution

When water begins to come out, the centre of mass begins to lower. There is an increase in the effective length and hence an increase in the time period : When water flows out completely, the centre of mass begins to shift back to the geometrical centre of the follow bob. So, there is a decrease in the effective length and hence a decrease in time period. When water flows out completely, the centre of mass is again at the geometrical centre. Now, the time period is the same as in the beginning.
Question 12
1 / -0

A uniform metre scale of length 1 m is balanced on a fixed semi-circular cylinder of radius 30 cm as shown in the figure. One end of the scale is slightly depressed and released. The time period (in seconds) of the resulting simple harmonic motion is

(Take g = 10 ms^-2)

A
π

B
π/2

C
π/3

D
π/4

Solution
Question 13
1 / -0

Two SHMs are respectively represented by y₁ = a sin (ωt - kx), and y₂ = b cos (ωt - kx). The phase difference between the two is:

A
π/2

B
π/4

C
π/6

D
3π/4

Solution

As

y1 = a sin (ωt - kx), and y2 = b cos (ωt - kx)

y2 = b sin (ωt - kx + (π/2))

Hence phase difference between them is π/2.
Question 14
1 / -0

The displacement y of a particle executing periodical motion is given by y = 4 cos² (t/2) sin (1000t). This expression may be considered to be a result of the superposition of how many independent harmonic motions?

A
5

B
4

C
3

D
2

Solution
Question 15
1 / -0

A particle in SHM is described by the displacement equation x(t) = A cos (ωt + θ). If the initial (t = 0) position of the particle is 1 cm and its initial velocity is π cm/s, then what is its amplitude? (The angular frequency of the particle is πs^-1.)

A
1 cm

B
√2 cm

C
2 cm

D
2.5 cm

Solution