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Physics questions for JEE Main — Mechanics, Electrostatics, Optics, Modern Physics.

434 Q 9 Topics Take Test

Difficulty: All Easy Medium Hard 31–40 of 434

Topics in JEE Physics

All Mechanics 100 Thermodynamics 100 Electrostatics 100 Current Electricity 100 Magnetism 100 Optics 100 Modern Physics 100 Semiconductors 100 Waves 100

Q.31 Medium Waves

A transverse wave on a string has amplitude A = 0.1 m and frequency f = 50 Hz. Maximum particle velocity is:

A 5π m/s

B 10π m/s

C 15π m/s

D 20π m/s

Correct Answer: B. 10π m/s

EXPLANATION

Maximum particle velocity = Aω = A(2πf) = 0.1 × 2π × 50 = 10π m/s

Test

Q.32 Medium Waves

When a wave passes from a less dense to a more dense medium, the phenomenon that does NOT occur is:

A Refraction

B Change in velocity

C Change in wavelength

D Change in frequency

Correct Answer: D. Change in frequency

EXPLANATION

Frequency remains constant when a wave passes between media. Velocity, wavelength, and direction (refraction) change, but frequency does not

Test

Q.33 Medium Waves

A stationary observer hears a frequency of 1100 Hz from a moving source. If the source is moving towards the observer with speed 10 m/s, and the actual frequency is 1000 Hz, what is the speed of sound?

A 300 m/s

B 320 m/s

C 330 m/s

D 340 m/s

Correct Answer: C. 330 m/s

EXPLANATION

Using f' = f(v/(v-vs)), 1100 = 1000(v/(v-10)). Solving: 1.1(v-10) = v, 0.1v = 11, v = 330 m/s

Test

Q.34 Medium Waves

Two identical sound sources emit waves in phase. An observer is at a point where the path difference is 1.5λ. What is the phase difference?

A π

B 2π

C 3π

D 4π

Correct Answer: C. 3π

EXPLANATION

Phase difference = (path difference/λ) × 2π = (1.5λ/λ) × 2π = 3π

Test

Q.35 Medium Waves

A pipe open at both ends resonates at a frequency of 500 Hz for the fundamental mode. If it is closed at one end, the fundamental frequency becomes:

A 125 Hz

B 250 Hz

C 500 Hz

D 1000 Hz

Correct Answer: B. 250 Hz

EXPLANATION

For open pipe: L = λ/2, For closed pipe: L = λ/4. Ratio of frequencies = 2:1. New frequency = 500/2 = 250 Hz

Test

Q.36 Medium Waves

A string of length 2 m vibrates in its third harmonic. The number of nodes (excluding ends) is:

A 1

B 2

C 3

D 4

Correct Answer: B. 2

EXPLANATION

In the nth harmonic, number of nodes excluding ends = n-1. For third harmonic, nodes = 3-1 = 2

Test

Q.37 Medium Waves

A source of frequency 500 Hz moves towards a stationary observer at 10 m/s. The speed of sound is 330 m/s. What is the apparent frequency heard by the observer?

A 515 Hz

B 530 Hz

C 545 Hz

D 560 Hz

Correct Answer: A. 515 Hz

EXPLANATION

Using Doppler effect, f' = f(v/(v-vs)) = 500(330/(330-10)) = 500(330/320) = 515.6 Hz ≈ 515 Hz

Test

Q.38 Medium Waves

For a stationary wave on a string fixed at both ends of length L = 1 m, the fundamental frequency is 100 Hz. What is the velocity of the transverse wave on the string?

A 50 m/s

B 100 m/s

C 200 m/s

D 400 m/s

Correct Answer: C. 200 m/s

EXPLANATION

For fundamental mode, L = λ/2, so λ = 2L = 2 m. v = fλ = 100 × 2 = 200 m/s

Test

Q.39 Medium Waves

In Young's double slit experiment, if the distance between slits is d, distance to screen is D, and wavelength is λ, the fringe width is:

A λd/D

B λD/d

C dD/λ

D λ/dD

Correct Answer: B. λD/d

EXPLANATION

Fringe width β = λD/d, where D is the distance to the screen and d is the slit separation

Test

Q.40 Medium Waves

When a wave reflects from a denser medium, the phase change is:

A 0°

B 90°

C 180°

D 270°

Correct Answer: C. 180°

EXPLANATION

Upon reflection from a denser medium (fixed end), there is a phase change of π radians or 180°

Test

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