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Topics in JEE Physics
Two sources of sound have intensities I₁ and I₂. The ratio of their amplitudes is:
Correct Answer:
A. √(I₁/I₂)
EXPLANATION
Since I ∝ A², the ratio A₁/A₂ = √(I₁/I₂)
A pipe closed at one end and open at the other has a length of 0.5 m. The fundamental frequency is (speed of sound = 340 m/s):
Correct Answer:
A. 170 Hz
EXPLANATION
For closed pipe, f₁ = v/(4L) = 340/(4×0.5) = 340/2 = 170 Hz
The intensity of a sound wave is I. If the amplitude is doubled and frequency is halved, the new intensity will be:
Correct Answer:
B. 2I
EXPLANATION
Intensity ∝ A²f². New intensity = (2A)² × (f/2)² × I/(A²f²) = 4 × (1/4) × I = 2I
A wave equation is given as y = 5sin(2πx/4 - 2πt/2). The amplitude and frequency are:
Correct Answer:
A. Amplitude = 5 m, Frequency = 1 Hz
EXPLANATION
From y = Asin(2πx/λ - 2πt/T), A = 5 m, and f = 1/T = 1/2π × 2π = 1 Hz
When two coherent light sources interfere, the condition for destructive interference is:
Correct Answer:
B. Path difference = (n+1/2)λ
EXPLANATION
For destructive interference, the path difference must be odd multiples of λ/2: (2n+1)λ/2 or (n+1/2)λ
A stationary observer hears a sound from an approaching source. The observed frequency is:
Correct Answer:
B. Greater than the actual frequency
EXPLANATION
Doppler effect: When source approaches observer, f' = f(v)/(v-vs), which is greater than f
A sound wave with frequency 500 Hz travels through air (speed = 330 m/s) and then enters water (speed = 1500 m/s). What happens to the wavelength?
Correct Answer:
B. Increases
EXPLANATION
Frequency remains constant during refraction. λ = v/f. Since speed increases from 330 to 1500 m/s, wavelength increases proportionally
