Sound MCQ: Introduction and Explanation

Answer: b) Longitudinal wave

Explanation: Sound waves are mechanical waves that require a medium to travel through, such as air, water, or solids. When a sound wave travels through a medium, the particles in the medium vibrate back and forth in the same direction as the wave. This type of wave is called a longitudinal wave.

• In a longitudinal wave, the wave energy travels in the same direction as the oscillations of the medium. 
• The particles in the medium move back and forth parallel to the direction of the wave, which creates areas of compression and rarefaction in the medium. 
• The compression regions represent areas of high pressure, while the rarefaction regions represent areas of low pressure.

Examples of longitudinal waves include sound waves in the air, seismic waves, and waves in springs and coils. Transverse waves, on the other hand, are waves in which the energy travels perpendicular to the oscillations of the medium. Electromagnetic waves, such as light and radio waves, do not require a medium to travel through and are not considered mechanical waves. Standing waves are stationary waves that occur when two waves with the same frequency and amplitude travel in opposite directions and interfere with each other.

Answer: d) Pitch

Explanation: The pitch of a sound refers to how high or low the sound is perceived to be. It is determined by the frequency of the sound wave, which is the number of complete cycles of compression and rarefaction that occur per unit of time. The higher the frequency, the higher the pitch of the sound.

• The amplitude of a sound wave refers to the strength or intensity of the wave, which determines how loud the sound is perceived to be. 
• The wavelength of a sound wave refers to the distance between two consecutive compressions or rarefactions in the medium and is related to the frequency and the speed of sound in the medium.

Therefore, the number of compressions or rarefactions per unit of time gives the characteristic of the pitch. This is because the frequency of the sound wave determines how frequently the particles in the medium vibrate back and forth, which determines the perceived pitch of the sound. Higher frequencies correspond to higher pitches, while lower frequencies correspond to lower pitches.

In summary, pitch is determined by the frequency of the sound wave, while loudness is determined by the amplitude of the sound wave, and wavelength is related to the frequency and speed of sound in the medium.

Answer: c) Rarefaction

Explanation: When a sound wave travels through a medium, it causes the particles in the medium to vibrate back and forth. As the vibrating object moves forward, it creates a region of high pressure called compression, where the particles are tightly packed together. Conversely, when the vibrating object moves backwards, it creates a region of low pressure called a rarefaction, where the particles are spread out.

• In a sound wave, these compressions and rarefactions alternate as the wave travels through the medium. 
• The compressions represent areas of high pressure, while the rarefactions represent areas of low pressure. 
• The amplitude of the wave is determined by the difference in pressure between the compressions and rarefactions.

Rarefaction is an important concept in understanding sound waves, as it is responsible for the perception of sound. When a rarefaction reaches our ears, it causes a decrease in pressure, which our ears perceive as a decrease in sound intensity or volume. The compression and rarefaction together create a wave pattern that travels through the air and eventually reaches our ears, allowing us to hear sound.

Therefore, the correct answer is option (c) Rarefaction.

Answer: d) Speed of sound

Explanation: Sound is a type of wave that travels through a medium, such as air, water, or solids. The speed of sound refers to the distance that a sound wave travels per unit of time. It is an important characteristic of sound, as it can vary depending on the medium that the sound is travelling through.

• The speed of sound can be calculated using the formula: speed = wavelength x frequency. 
• The wavelength is the distance between two consecutive compressions or rarefactions in a sound wave, while the frequency is the number of waves that pass a given point in one second. 
• Since the distance travelled by one compression or rarefaction in one wave is equal to the wavelength, the speed of sound can be expressed as the product of wavelength and the number of waves passing a point in one second, which is the frequency.

Therefore, the correct answer is option (d) Speed of sound. The distance travelled by one compression or rarefaction per unit of time gives the speed of sound. The wavelength and frequency are related to the speed of sound, but they alone do not give us the speed of sound.

Answer: c) Compression

Explanation: When a body vibrates, it causes the air molecules around it to also vibrate. As the vibrating object moves forward, it compresses the air in front of it, creating a region of high pressure called compression. This compression represents a high-density area of air, where the air particles are pushed together tightly.

• In a sound wave, compressions and rarefactions alternate as the wave travels through a medium. 
• The compressions represent areas of high pressure, while the rarefactions represent areas of low pressure. 
• The amplitude of the wave is determined by the difference in pressure between the compressions and rarefactions.

Compression is an important concept in understanding sound waves, as it is responsible for the perception of sound. When a compression reaches our ears, it causes an increase in pressure, which our ears perceive as an increase in sound intensity or volume.

Therefore, the correct answer is option (c) Compression.

Answer: c) Echo

Explanation: When a sound wave travels through a medium, it can bounce off a surface and return to the listener. This phenomenon is known as an echo. The reflection of sound waves is a common occurrence in our daily lives and can be heard in various environments such as mountains, valleys, buildings, and enclosed spaces.

• An echo occurs when the time it takes for the sound wave to travel to the reflecting surface and back is greater than the time interval between successive sound waves produced by the source. 
• This time interval is called the persistence of hearing. 
• If the reflection occurs within this time interval, the sound produced will be heard as a distinct echo. 
• If the reflection occurs after the persistence of hearing has ended, the sound will be perceived as a part of the overall sound, and not as a separate echo.

Echoes can be used to measure the distance between the source and the reflecting surface. This is done by measuring the time interval between the production of the sound wave and the detection of the echo. The speed of sound in air is approximately 343 meters per second, so the distance between the source and the reflecting surface can be calculated using the formula: distance = speed of sound × time interval / 2.

Therefore, the correct answer is option (c) Echo.

Answer: d) Timber

Explanation: Sound waves are characterized by several properties, including amplitude, wavelength, frequency, and timber (or timbre). While pitch and loudness are two key characteristics of sound, they are not the only factors that distinguish one sound from another. 

• Timber, or timbre, refers to the unique quality or colour of a sound, which allows us to distinguish between different instruments or voices, even if they are playing or singing the same note at the same volume.
• Timber is determined by the complex mixture of frequencies that make up a sound wave. 
• Even when two sounds have the same pitch and loudness, they can still have different timbers. 
• For example, a guitar and a piano playing the same note will have different timbers due to the unique way in which each instrument produces sound.

Amplitude refers to the intensity or strength of a sound wave and determines the loudness of the sound. Wavelength and frequency are related properties that determine the pitch of a sound. Shorter wavelengths and higher frequencies result in higher-pitched sounds, while longer wavelengths and lower frequencies result in lower-pitched sounds.

Therefore, the correct answer is option (d) Timber, as it is the property that allows us to distinguish between sounds that have the same pitch and loudness but different qualities.

Answer: d) Temperature of the medium

Explanation: The speed of sound is a measure of how quickly a sound wave travels through a medium, such as air or water. The speed of sound is determined by various factors, including the temperature of the medium, the density of the medium, and the elasticity of the medium.

• The temperature of the medium is the most significant factor affecting the speed of sound.
• In general, as the temperature of the medium increases, the speed of sound also increases. 
• This is because, at higher temperatures, the molecules in the medium have more kinetic energy, which makes them vibrate more quickly and travel further in a given time. 
• This results in an increase in the speed of sound.
• On the other hand, at lower temperatures, the molecules in the medium move more slowly and are less likely to collide with one another, resulting in a decrease in the speed of sound.

The density and elasticity of the medium also play a role in determining the speed of sound. In general, the denser and more elastic the medium, the higher the speed of sound. However, these effects are relatively small compared to the effect of temperature.

Therefore, the correct answer is option (d) Temperature of the medium.

Answer:  c) Ultrasound

Explanation: Dolphins, bats, and porpoises use ultrasound to communicate with each other and locate objects in their environment. Ultrasound is a type of sound wave that has a frequency higher than what the human ear can hear. Dolphins, bats, and porpoises are all capable of producing high-frequency sounds using specialized structures in their bodies, such as the nasal passages of dolphins and the larynx of bats.

• When these animals emit ultrasound waves, the waves travel through the air or water and bounce off of objects in their environment. 
• By measuring the time it takes for the waves to bounce back, these animals can determine the location, size, and shape of objects around them. 
• This process is called echolocation and is critical for these animals to navigate and hunt in their environment.
• Ultrasound is also used in human technology, such as medical imaging and industrial testing. 
• In medical imaging, high-frequency sound waves are used to create images of the inside of the body, allowing doctors to diagnose and treat medical conditions. 
• In industrial testing, ultrasound is used to detect flaws in materials and structures, such as cracks in metal pipes.

Therefore, the correct answer is option (c) Ultrasound.

Answer: The correct answer is c. The frequency of the sitar string with the frequency of other musical instruments.

Explanation: The sitar is a stringed instrument that is often used in Indian classical music. In an orchestra, it is important that all the musical instruments are in tune with each other. The sitarist adjusts the tension and plucks the string in such a way that the frequency of the sitar string matches the frequency of other musical instruments. This ensures that the sitar sound blends well with the other musical instruments and the overall sound of the orchestra is harmonious.

• Option a is incorrect because adjusting the tension and plucking the string does not directly affect the volume of the sitar. 
• Option b is incorrect because adjusting the tension and plucking the string does not directly affect the color of the sitar sound. 
• Option d is incorrect because adjusting the tension and plucking the string does not directly affect the pitch of the sitar.

In conclusion, adjusting the tension and plucking the string suitably helps the sitarist to match the frequency of the sitar string with the frequency of other musical instruments, thus ensuring a harmonious sound in an orchestra.