Tag: physics

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Questions Related to physics

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

The sound intensity is 0.008 $W/m^2$ at a distance of 10 m from an isotropic point source of power of the source is approximately :

  1. 2.5 watt

  2. 0.8 watt

  3. 8 watt

  4. 10 watt
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

Intensity I = P / (4 * pi * r^2). Given I = 0.008 and r = 10, P = I * 4 * pi * r^2 = 0.008 * 4 * 3.14 * 100 = 0.008 * 1256 = 10.048 watts, which is approximately 10 watts.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

The driver of a car travelling at the speed of $30m/sec$ towards a hill sounds a horn of frequency $600\ Hz$. If the velocity of sound in air is $330m/s$, the frequency of reflected sound as heard by the driver is

  1. $500\ Hz$

  2. $550\ Hz$

  3. $555.5\ Hz$

  4. $720\ Hz$
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The frequency heard by the hill is f' = f * (v / (v - vs)) = 600 * (330 / (330 - 30)) = 600 * (330 / 300) = 660 Hz. This reflected sound acts as a source moving towards the driver, so f'' = f' * ((v + vo) / v) = 660 * ((330 + 30) / 330) = 660 * (360 / 330) = 720 Hz.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

Ultrasonic, intrasonic and audible waves travel through a medium with speeds $V _u,V _i,$ and $V _a$ respectively, then (given constant temperature)

  1. $V _i=V _a=V _u$

  2. $V _u>V _a>V _i$

  3. $V _u < V _a < V _i $

  4. ${ V } _{ a }\le { V } _{ u }={ V } _{ i }$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

The speed of sound in a medium depends on the properties of the medium (density, elasticity) and temperature, not on the frequency of the sound wave.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

A man fires a gun and hears the echo after $2\,\frac{1}{2}sec$. If the velocity of sound in air is $340ms^{-1}$ his distance from the cliff causing the echo is 

  1. $2\,\frac{1}{2}km$

  2. $425m$

  3. $850m$

  4. $136m$
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Total distance traveled by sound is 2 * d = v * t. d = (v * t) / 2 = (340 * 2.5) / 2 = 340 * 1.25 = 425 m.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

A sound wave of pressure amplitude $5$ pascal propagates through the air medium. The normal pressure of air is $1.0\times10^5 N/m^2$. The difference between maximum and minimum pressure in the medium is 

  1. $5\times10^5 N/m^2$

  2. $10\times10^5 N/m^2$

  3. $10 N/m^2$

  4. $None\ of\ these$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The pressure amplitude is the difference between the maximum pressure and the ambient pressure. The difference between maximum and minimum pressure is twice the pressure amplitude: 2 * 5 = 10 N/m^2.

Multiple choice physics range of hearing sound: production of sound audible, infrasonic and ultrasonic sounds different sounds

A siren emitting a sound of frequency $1000 Hz$ moves away from you towards a cliff at a speed of $10 m/s$ [speed of sound in air $330 m/s$] Then. 

  1. The frequency of the sound you hearing coming directly from the siren is $ \dfrac {33}{34} \times 1000 Hz $.

  2. The frequency of the sound you hearing coming directly from the siren is $ \dfrac {33}{32} \times 1000 Hz $.

  3. The frequency of the sound you hear reflect off the cliff $ \dfrac {33}{32} \times 1000 Hz $.

  4. The frequency of the sound you hear reflect off the cliff $ \dfrac {33}{34} \times 1000 Hz $.
Reveal answer Fill a bubble to check yourself
C Correct answer