Physics Test 252

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Physics Test 252

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Question 1
4 / -1

The engine of a motorboat is switched off when its speed is v0. If motorboat experiences variable acceleration as dv/dt = −βv³, where β is a positive constant and v instantaneous speed, then the speed of motorboat after t second (t = 0 when switch is off) is

A

B

C

D

Solution
Question 2
4 / -1

In a photodiode, the conductivity increases when the material is exposed to light. It is found that conductivity changes only if the wavelength is less than 600 nm. What is the bandgap?

A
2.06 eV

B
1.2 eV

C
3.4 eV

D
4.2 eV

Solution

Given,

The maximum wavelength of light, which increases the conductivity, λ = 600 nm

Hence the energy of this photon must be equal to band gap (E_g).
Question 3
4 / -1

If the magnetic dipole moment of an atom of diamagnetic material, paramagnetic material and ferromagnetic material is denoted by μ_d, μ_p and μ_f respectively, then

A
μ_d = 0 and μ_p≠ 0

B
μ_d ≠ 0 and μ_p = 0

C
μ_p = 0 and μ_f ≠ 0

D
μ_d ≠ 0 and μ_f≠ 0

Solution

The magnetic dipole moment of a diamagnetic material is zero as each of its pair of electrons has opposite spins, i.e., μ_d = 0. Paramagnetic substances have dipole moment > 0, i.e., μp ≠ 0, because of the excess of electrons in its molecules spinning in the same direction.

Ferromagnetic substances are very strong magnets and they also have a permanent magnetic moment, i.e., μ_f ≠ 0.
Question 4
4 / -1

Which of the following will pair up to produce stationary wave?

(1) Z₁ = A cos(kx − ωt)
(2) Z₂ = A cos(kx + ωt)
(3) Z₃ = A cos(ky − ωt)
(4) Z₄ = A cos(kz + ωt)

A
1 and 2

B
2 and 3

C
3 and 4

D
1 and 3

Solution

Stationary waves are produced by two identical waves travelling in opposite direction in same plane.

∴ for stationary wave

Z₁ = A cos(kx − ωt)

Z₂ = A cos(kx + ωt)
Question 5
4 / -1

A particle is undergoing SHM. Displacement vs time curve is as shown in the figure.

A
Phase of the oscillator is same at t = 0 s and t = 2 s.

B
Phase of the oscillator is same at t = 2 s and t = 5 s.

C
Phase of the oscillator is same at t = 1 s and t = 7 s.

D
Phase of the oscillator is same at t = 1 s and t = 5 s.

Solution

The phase of a particle executing SHM is defined as the state of a particle as regard to its position and direction of motion at any instant of time. In the given curve, phase is same when t = 1 s and t = 5 s. Also phase is same when t = 2 s and t = 6 s.
Question 6
4 / -1

Match List - I (Electromagnetic wave type) with List - II (Its association/application) and select the correct option from the choices given below the lists :

A

B

C

D

Solution

Infrared - Muscular treatment

Radio wave - Broadcasting

X Rays - To detect fracture

Uv Rays → Absorbed ozone layer
Question 7
4 / -1

Figure shows a cyclic process ABCDBEA performed on an ideal cycle. If P_A = 2 atm, P_B = 5 atm and P_C = 6 atm, V_E – V_A = 20 litre, find the work done (in KJ) by the gas in the complete process. (1 atm. pressure = 1 × 10⁵ Pa)

A
2.67

B
3.18

C
4.27

D
1.37

Solution
Question 8
4 / -1

In the circuit shown, the key (K) is closed at t = 0, the current through the key at the t = 10⁻³ln² s; is.

A
2A

B
3.5A

C
2.5A

D
Zero

Solution
Question 9
4 / -1

If first excitation potential of a hydrogen like atom is V electron volt, then the ionization energy of this atom will be:

A
V electron volt

B
3V/4 electron volt

C
4V/3 electron volt

D
cannot be calculated by given information,

Solution
Question 10
4 / -1

Let ω is the angular velocity of the earth's rotation about its own axis and acceleration due to gravity on the earth's surface at the poles is g. An object weighed by a spring balance gives the same reading at the equator, as well as at a height h above the poles (h ≪ R). What is the value of h ?

A

B

C

D

Solution

The value of acceleration due to gravity at the equator is g_E= g − Rω² and the acceleration due to gravity at a height h above the pole is It is given that