Physics Test 54

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Physics Test 54

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Weekly Quiz Competition

Question 1
4 / -1

Two ideal junction diodes D₁ and D₂are connected to a battery as shown in the figure. What is the current supplied by the battery if its terminals are interchanged?

A
0.25 A

B
0.5 A

C
0.75 A

D
zero

Solution

When the terminals are reserved D₁ is then reverse biased which will fetch no current, so the resistance 10 ohm is out from the scene now, the current is equal to the resistance and since D₂ is forward biased 20 ohm resistance will only be counted therefore current is equal to 5/20 = 0.25A.

Hence, the correct option is (A).
Question 2
4 / -1

A passenger train moving at a speed of 5 ms^-1 is followed by an express train moving on the same track at a speed of 30 ms^-1. The rear side of the passenger train is at some distance. The driver of the express train applies brakes to avoid a collision. If the retardation due to brakes is 4 ms^-2, then find the time in which the accident is avoided after the application of brakes.

A
4.25 s

B
5.25 s

C
6.25 s

D
7.25 s

Solution

The initial relative velocity of the express train w.r.t the passenger train,

u_ep= u_e−u_p

=30−5

=25 ms−1

The final relative velocity of the express train w.r.t the passenger train,

v_ep=0 (because the express train comes to rest relative to the passenger train)

From the first equation of motion,

v_eq=u_ep−at

⇒0 = 25−4t

⇒ 4t = 25

⇒ t = 6.25 s

Hence, the correct option is (C).
Question 3
4 / -1

A table tennis ball that has been covered with a conducting point is suspended by a light thread so that it hangs between two metal p.a.es. One plate is earthed, while the other is attached to a high voltage generator, the ball

A
Hangs without moving

B
Swings backward & forward hitting each plate in turn

C
Is attracted to the high voltage plate and stays there

D
Is repelled by an earthed plate and stays there

Solution

By induction, the tennis ball gets -ve charge and gets attracted to the +ve plate and touches it. Charges are then shared, as charges repel and hence ball moves away & touches the earthed plate which gives its charge and goes to initial position & process repeats.

Hence, the correct option is (B).
Question 4
4 / -1

The ratio of nuclear radii and nuclear densities of ₂₆Fe⁵⁶ and ₉₂U²³⁸is

A
0.671 and 1 respectively

B
1 and .671 respectively

C
Both equal to

D
Both equal to . 671

Solution
Question 5
4 / -1

In Young's double slit experiment, if the distance between the slits and the screen is doubled and the separation between the slits is reduced to half, the fringe width

A
Is doubled

B
Becomes four times

C
Is halved

D
Remains unchanged

Solution

Fringe width β = Dλ/d

where D is the distance between slits and screen

and d is the distance between the slits.

Thus, From question D′=2D and d′= d/2

When D is doubled and d is reduced to half, then the fringe width becomes

β′ = λ2D/ (d/2)

=4λD / d

=4β

Thus, when the double slit experiment the distance between the slits and the screen is doubled and the separation between the slits is reduced to half, the fringe width becomes four times.

Hence, the correct option is (B).
Question 6
4 / -1

The phase difference between two waves represented by where x is expressed in metres and t is expressed in seconds, is approximately

A
1.07 rad

B
2.07 rad

C
0.05 rad

D
1.5 rad

Solution
Question 7
4 / -1

The maximum number of possible interference maxima for slit-separation equal to twice the wavelength in Young's double-slit experiment, is

A
Infinity

B
5

C
3

D
Zero

Solution

The condition for maxima in Young's double-slit experiment is dsin⁡θ = nλ where d is the separation between the slits and λ is the wavelength of light used.

The maxima that are farthest from the slits is infinitely up or infinitely down the screen and corresponds to θ = π/2.

So, with the given condition, we have, n = dsin ⁡t(90^∘) / λ

= d/λ

=2

Thus, we have two maxima on the screen on either side of the central maxima. Thus, the maximum number of possible maxima observed are 2 + 1 + 2 = 5.

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

An ideal gas has pressure ′p′, volume ′v′ and absolute temperature ′T′. It ′m′ is the mass of each molecule and ′K′ is the Boltzmann constant, the density of the gas is

A
mkT

B
P / kT

C
p / kvT

D
P_m/ kT

Solution
Question 9
4 / -1

If a transformer of an audio amplifier has an input impedance of 8Ω and output impedance of 8 kΩ, the primary and secondary turns of this transformer connected between the output of the amplifier and to loudspeaker should have the ratio

A
1000 :1

B
100 : 1

C
1 : 32

D
32 : 1

Solution

If a transformer of an audio amplifier has an input impedance of 8Ω output impedance of 8 kΩ, the primary and secondary turns of this transformer connected between the output of the amplifier and to loudspeaker should have the ratio will be 1:32.

Hence, the correct option is (C).
Question 10
4 / -1

An inductor of self-inductance 100 mH and a resistor of resistance 50 Ω, are connected to a 2 V battery. The time required for the current to come to half its steady value is

A
2 millisecond

B
2ln⁡(0.5) millisecond

C
2ln⁡(3) millisecond

D
2ln⁡(2) millisecond

Solution