Govt. Exams
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Topics in JEE Physics
A person hears sound from two sources with frequencies 400 Hz and 404 Hz. The beat frequency heard is:
Correct Answer:
B. 4 Hz
EXPLANATION
Beat frequency = |f₁ - f₂| = |400 - 404| = 4 Hz
Standing waves are formed on a string by superposition of two waves traveling in opposite directions with:
Correct Answer:
C. Same amplitude, frequency, and wavelength
EXPLANATION
Standing waves form from superposition of two waves with equal amplitude, frequency, and wavelength traveling in opposite directions
A longitudinal wave has frequency 50 Hz and wavelength 8 m. The wave velocity is:
Correct Answer:
A. 400 m/s
EXPLANATION
v = fλ = 50 × 8 = 400 m/s
A string of length 1 m is fixed at both ends. The fundamental frequency is 100 Hz. What is the frequency of the third harmonic?
Correct Answer:
C. 300 Hz
EXPLANATION
For a string fixed at both ends, f_n = n × f₁. Third harmonic: f₃ = 3 × 100 = 300 Hz
Two waves of equal amplitude and slightly different frequencies are superposed. The resulting pattern is called:
Correct Answer:
B. Beats
EXPLANATION
When two waves of slightly different frequencies interfere, alternating constructive and destructive interference produces beats with beat frequency = |f₁ - f₂|
The equation of a wave is y = 0.06 sin(100t - 8x), where x and y are in meters and t is in seconds. The wavelength is:
Correct Answer:
A. 0.785 m
EXPLANATION
From equation, wave number k = 8 rad/m. λ = 2π/k = 2π/8 = 0.785 m
A harmonic wave travels along a string with amplitude 2 cm and wavelength 40 cm. If the wave completes 10 oscillations in 5 seconds, what is the wave velocity?
Correct Answer:
A. 80 cm/s
EXPLANATION
Frequency f = 10/5 = 2 Hz, λ = 40 cm, v = fλ = 2 × 40 = 80 cm/s
The intensity of a sound wave is inversely proportional to which of the following?
Correct Answer:
B. Distance squared from point source
EXPLANATION
For a point source, intensity I ∝ 1/r². This is the inverse square law for spherical waves
A longitudinal wave has a wavelength of 4 m and speed 400 m/s. The frequency of the wave is:
Correct Answer:
C. 100 Hz
EXPLANATION
f = v/λ = 400/4 = 100 Hz
The period of a wave is 0.02 seconds. What is its frequency?
Correct Answer:
B. 50 Hz
EXPLANATION
f = 1/T = 1/0.02 = 50 Hz
