HSSC-1 (Class-11) Solved Physics MCQs; Unit-8: Waves;  (New Book/KPK Text Board, Peshawar) With Verified Answers 


1. When a wave goes from one medium to another medium, which one of the following characteristics of the wave remains constant?




... Answer is B. Frequency
Velocity, Wavelength, and phase are changed and only frequency remains the same


2. When a transverse wave is reflected from the boundary of a denser to a rarer medium, it undergoes a phase change of




... Answer is C. 𝝅
The phase change of 180° = 𝝅


3. If the tension in the string is doubled and its mass per unit length if is reduced to half. Then the speed of the transverse wave on it is




... Answer is A. Doubled
v = `\ sqrt frac {T}{μ}` 👉 T' = 2T and μ' =`\frac {μ}{2}` 👉 v' = `\ sqrt frac {2T}{μ/2}` 👉 v' = `\ sqrt frac {4T}{μ}` 👉 v' = 2`\ sqrt frac {T}{μ}` 👉 v' = 2v


4. Which one of the following properties is not exhibited by the longitudinal waves?




... Answer is D. Polarization
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5. A sounding source and a listener are both at rest relative to each other. If the wind blows from the listener towards the source, then which one of the following sounds will change?




... Answer is B. Speed
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6. Which one of the following factors has no effect on the speed of sound in a gas?




... Answer is B. Pressure
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7. There is no net transfer of energy by particles of medium in :




... Answer is D. Stationary wave
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8. Which one of the following could be the frequency of ultraviolet radiation?




... Answer is D. 1.0 x 10¹⁵ Hz
Given: ---------------------------------


9. When a stationary wave is formed then its frequency is





... Answer is A. Same as that of the individual waves
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10. The fundamental frequency of a closed organ pipe is f. If both ends are opened then its fundamental frequency will be




... Answer is C. 2f
Fundamental frequency of open pipe f (open) = `\ frac {V}{2L}` 👉 Fundamental frequency of closed pipe f (closed) = `\ frac {V}{4L}` 👉 Now f (open) = `\ frac {V}{2L}` = `\ frac {V}{2L}` 𝐱 `\ frac {2}{2}` = 2 `\ frac {V}{4L}` = 2 f (closed)


11. If the amplitude of a wave is doubled, then its intensity is




... Answer is C. quadrupled
Intensity is directly proportional to the square of the amplitude of the wave i.e I ∝ X₀² 👉 when X₀' = 2X₀ 👉 I' ∝ (2X₀)² 👉 I' ∝ 4X₀² 👉 I' ∝ 4I


12. A sound source is moving toward a stationary listener at 1/10th of the speed of sound. The ratio of apparent to real frequency is :




... Answer is D. `\ frac {10}{9}`
f' = `\ frac {v}{v - a}` f 👉 a = `\ frac {1}{10}` (given) 👉 f' = `\ frac {v}{v - frac {1}{10}}` f = `\ frac {10}{9}`f 👉 `\ frac {f'}{f}` = `\ frac {10}{9}`




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