Govt. Exams
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Topics in JEE Physics
Two waves of the same frequency interfere constructively. The amplitude of the first wave is 3 units and the second is 4 units. What is the maximum resultant amplitude?
Correct Answer:
B. 7 units
EXPLANATION
For constructive interference, A_resultant = A₁ + A₂ = 3 + 4 = 7 units
The speed of light in a medium is 2×10⁸ m/s. What is the refractive index of the medium?
Correct Answer:
B. 1.5
EXPLANATION
n = c/v = (3×10⁸)/(2×10⁸) = 1.5
A wave travels along a string with velocity v = 20 m/s. If the frequency is 50 Hz, what is the wavelength?
Correct Answer:
A. 0.4 m
EXPLANATION
Using v = fλ, we get λ = v/f = 20/50 = 0.4 m
Energy of a harmonic wave is proportional to:
Correct Answer:
B. Square of amplitude
EXPLANATION
Energy E ∝ A² for harmonic waves. Kinetic energy = (1/2)mω²A²sin²(ωt)
A standing wave is formed on a string. At a node, the particle velocity is always:
Correct Answer:
B. Zero
EXPLANATION
At nodes, particles do not move. Amplitude of oscillation is zero, hence particle velocity is always zero
The intensity of a sound wave at distance r from a point source varies as:
Correct Answer:
C. I ∝ 1/r²
EXPLANATION
For a point source, intensity spreads over a sphere of area 4πr², so I ∝ 1/r²
A tuning fork vibrates at 440 Hz. If the speed of sound is 330 m/s, what is the wavelength of sound produced?
Correct Answer:
C. 0.75 m
EXPLANATION
λ = v/f = 330/440 = 0.75 m
The equation of a wave is y = 5sin(2πt/0.04 - 2πx/0.8) m. What is the wave velocity?
Correct Answer:
B. 20 m/s
EXPLANATION
From y = Asin(ωt - kx), ω = 2π/0.04 = 50π, k = 2π/0.8 = 2.5π. v = ω/k = 50π/2.5π = 20 m/s
Two waves of frequencies 256 Hz and 260 Hz are produced simultaneously. What is the beat frequency?
Correct Answer:
B. 4 Hz
EXPLANATION
Beat frequency = |f₁ - f₂| = |256 - 260| = 4 Hz
A wave travels on a string with velocity v = 20 m/s. If the frequency is 50 Hz, what is the wavelength?
Correct Answer:
A. 0.4 m
EXPLANATION
Using v = fλ, we get λ = v/f = 20/50 = 0.4 m
