Sound Archives

1. Which one among the following statements regarding sound is correct ?

Which one among the following statements regarding sound is correct ?

High pitch sound has high frequency

High pitch sound has high amplitude

High pitch sound has high speed

High pitch sound has low frequency and high amplitude

This question was previously asked in

UPSC CISF-AC-EXE – 2023

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The correct answer is A.

Pitch of a sound is related to its frequency. A higher frequency corresponds to a higher pitch, and a lower frequency corresponds to a lower pitch. Amplitude of a sound wave is related to its loudness or intensity. Speed of sound depends on the medium through which it travels and generally does not change with pitch or amplitude.

This is a fundamental concept in the physics of sound waves. Frequency is measured in Hertz (Hz), and amplitude is related to the displacement or pressure variation in the medium.

2. Which one of the following is the audible range of hearing for humans

Which one of the following is the audible range of hearing for humans ?

20 kHz – 200 kHz

20 Hz – 20 kHz

20 Hz – 35 kHz

20 Hz – 40 kHz

This question was previously asked in

UPSC CAPF – 2024

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The correct option is B. The generally accepted audible range of hearing for young, healthy humans is from 20 Hz to 20 kHz.

– ‘Hz’ stands for Hertz, which is a unit of frequency (cycles per second).
– ‘kHz’ stands for kilohertz, which is 1000 Hertz.
– The lower limit of human hearing is around 20 Hz, and the upper limit is around 20,000 Hz (20 kHz).

Hearing range can vary between individuals and typically decreases with age, especially at higher frequencies. Frequencies below 20 Hz are called infrasound, and frequencies above 20 kHz are called ultrasound. Humans cannot hear these sounds, although some animals can.

3. A sound wave of frequency of 2 kHz has a wavelength of 35 cm in a give

A sound wave of frequency of 2 kHz has a wavelength of 35 cm in a given medium. How long will it take to travel a distance of 2⋅1 km through the medium ?

30 s

2⋅1 s

3⋅0 s

4⋅1 s

This question was previously asked in

UPSC CAPF – 2023

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The correct answer is C. We need to calculate the time taken using the relationship between speed, distance, and time, after first determining the speed of the sound wave.

– The speed of a wave ($v$) is given by the product of its frequency ($f$) and wavelength ($\lambda$): $v = f \times \lambda$.
– Given $f = 2 \text{ kHz} = 2000 \text{ Hz}$ and $\lambda = 35 \text{ cm} = 0.35 \text{ m}$.
– Speed $v = 2000 \text{ Hz} \times 0.35 \text{ m} = 700 \text{ m/s}$.
– The time ($t$) taken to travel a distance ($d$) is given by $t = d / v$.
– Given $d = 2.1 \text{ km} = 2100 \text{ m}$.
– Time $t = 2100 \text{ m} / 700 \text{ m/s} = 3 \text{ seconds}$.

The units were carefully converted to meters and seconds before calculation to ensure consistency in the final answer. The frequency is given in kilohertz (kHz) and the wavelength in centimeters (cm), requiring conversion to standard SI units (Hz and m). The distance is given in kilometers (km), also requiring conversion to meters.

4. Which one of the following phenomena CANNOT be exhibited by sound wave

Which one of the following phenomena CANNOT be exhibited by sound waves ?

Reflection

Refraction

Interference

Polarisation

This question was previously asked in

UPSC CAPF – 2019

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Sound waves are longitudinal waves, meaning the oscillations of the medium particles are parallel to the direction of wave propagation. Polarisation is a phenomenon exhibited only by transverse waves, where oscillations occur perpendicular to the direction of propagation, allowing them to be restricted to a specific plane. Since sound waves in air are longitudinal, they cannot be polarised.

The key principle here is understanding the difference between longitudinal and transverse waves and which wave phenomena apply to each. Polarisation is a characteristic property of transverse waves.

Sound waves can exhibit reflection (e.g., echoes), refraction (bending of sound waves when passing from one medium to another or through variations in temperature/density within a medium), and interference (superposition of waves resulting in constructive or destructive effects). These phenomena are common to both longitudinal and transverse waves under appropriate conditions. Sound waves can be transverse in solid materials, but typically when discussing ‘sound waves’ in the context of common phenomena, it refers to sound in air or liquids, which is longitudinal.

5. The Stethoscope used by a medical practitioner is based on the phenome

The Stethoscope used by a medical practitioner is based on the phenomenon of :

multiple reflection of sound waves.

scattering of sound waves.

refraction of sound waves.

none of the above.

This question was previously asked in

UPSC CAPF – 2010

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The stethoscope works based on the phenomenon of multiple reflection of sound waves.

– Sound waves generated inside the body (like heartbeats or breathing sounds) are collected by the diaphragm (or bell) of the stethoscope.
– These sound waves travel through the hollow tube. As they travel, they undergo multiple reflections off the inner walls of the tube.
– These repeated reflections guide the sound waves towards the earpieces, concentrating the sound and making it audible to the medical practitioner.

While sound can scatter or refract, the primary mechanism by which sound is transmitted and focused through the stethoscope tube to the listener’s ears is multiple internal reflection.

6. Which one of the following statements is true for sound waves propagat

Which one of the following statements is true for sound waves propagating in air ?

Sound is an electromagnetic wave and transverse in nature

Sound is a mechanical wave and longitudinal in nature

Sound is a mechanical wave and transverse in nature

Sound is an electromagnetic wave and longitudinal in nature

This question was previously asked in

UPSC NDA-2 – 2023

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Sound waves require a medium (like air, water, or solids) to travel, meaning they are mechanical waves. They propagate through the vibration of particles of the medium. In air, sound waves cause compressions and rarefactions as the air particles oscillate back and forth in the same direction as the wave is moving. This type of wave where particle oscillation is parallel to the direction of wave propagation is called a longitudinal wave. Electromagnetic waves, like light, do not require a medium and are transverse, with electric and magnetic fields oscillating perpendicular to the direction of propagation.

– Sound waves are mechanical waves because they need a medium to travel.
– In fluids (like air and water), sound waves are longitudinal waves, meaning particle motion is parallel to wave propagation.
– In solids, sound can propagate as both longitudinal and transverse waves.

Examples of longitudinal waves include sound waves in air, pressure waves, and seismic P-waves. Examples of transverse waves include light waves, radio waves, waves on a string, and seismic S-waves (in solids).

7. A microphone converts

A microphone converts

electrical signals to sound waves

sound waves to electrical signals

microwaves to sound waves

sound waves to microwaves

This question was previously asked in

UPSC NDA-2 – 2022

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A microphone converts sound waves into electrical signals.

– A microphone is a transducer, a device that converts one form of energy into another.
– Its function is to capture sound (which consists of variations in air pressure) and transform it into a corresponding electrical voltage or current signal.
– Different types of microphones use different principles (e.g., electromagnetic induction in dynamic microphones, capacitance change in condenser microphones) to achieve this conversion.
– The electrical signal produced by a microphone can then be amplified, recorded, or transmitted.

Conversely, a loudspeaker or headphone is a transducer that performs the opposite function: it converts an electrical signal into sound waves.

8. Which one of the following statements about the speed of sound waves i

Which one of the following statements about the speed of sound waves is not correct?

The speed of sound waves in steel is higher than that in water.

The speed of sound waves in air decreases with increase in temperature.

The speed of sound waves in air increases with increase in temperature.

The speed of sound waves in water is higher than that in air.

This question was previously asked in

UPSC NDA-2 – 2022

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The statement that the speed of sound waves in air decreases with increase in temperature is incorrect.

– The speed of sound is generally highest in solids, lower in liquids, and lowest in gases. This is because molecules are closer together and interact more strongly in denser media, allowing vibrations to propagate faster.
– The speed of sound in steel is higher than in water, and the speed of sound in water is higher than in air.
– The speed of sound in a gas (like air) increases with increasing temperature. As temperature rises, the average kinetic energy of the gas molecules increases, and they collide more frequently and vigorously, allowing the sound wave to travel faster.

The speed of sound in dry air at 0°C is approximately 331.3 m/s. For every degree Celsius increase in temperature, the speed increases by about 0.6 m/s. Therefore, speed increases with temperature.

9. SONAR is a device that is used to measure the distance of underwater o

SONAR is a device that is used to measure the distance of underwater objects by a ship. Which of the following types of waves does it use for this purpose?

Infrasonic waves

Sound waves in audible range for human beings

Ultrasonic waves

All of the above

This question was previously asked in

UPSC NDA-2 – 2022

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SONAR (Sound Navigation and Ranging) systems typically use ultrasonic waves to measure distances and detect underwater objects.

– SONAR works by emitting sound pulses and measuring the time it takes for the echo to return after bouncing off an object.
– The speed of sound in water is known, so the distance can be calculated from the travel time.
– Ultrasonic waves (frequencies above the human hearing range, typically >20 kHz) are preferred in SONAR for several reasons, including better directionality, less attenuation over typical ranges compared to higher frequencies, and superior resolution compared to lower (infrasonic or audible) frequencies for object detection.

SONAR can be active (emitting pulses) or passive (listening to sounds). Active SONAR, used for distance measurement, relies heavily on the properties of ultrasonic pulses. While lower frequencies might be used for long-range detection (where attenuation is lower), ultrasonic frequencies are standard for detailed navigation and object location applications described in the question.

10. When the pitch of sound increases, which one of the following

When the pitch of sound increases, which one of the following increases?

Intensity

Loudness

Wavelength

Frequency

This question was previously asked in

UPSC NDA-2 – 2022

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The correct answer is Frequency.

The pitch of a sound is determined by its frequency. A higher frequency corresponds to a higher pitch, and a lower frequency corresponds to a lower pitch.

Intensity is related to the amplitude of the sound wave and is perceived as loudness. Wavelength is inversely proportional to frequency for a constant speed of sound. Loudness is the subjective perception of sound intensity.