Sound Chapter of Class 9

What type of waves are sound waves?

• Heat waves

• Electromagnetic waves

• Light waves

• Mechanical waves

Define pitch in terms of sound.

• Pitch is the volume of a sound wave.

• Pitch is the duration of a sound wave.

• Pitch in terms of sound is the perceived frequency of a sound wave.

• Pitch is the timbre of a sound wave.

What is the unit of frequency?

• Newton

• Volt

• Hertz (Hz)

• Watt

What is the speed of sound in air at 20°C?

• 343 meters per second

• 500 meters per second

• 400 meters per second

• 256 meters per second

Explain the phenomenon of reflection of sound.

• Sound reflection occurs when sound waves pass through a surface without any change.

• Reflection of sound is caused by the absorption of sound waves by a surface.

• Sound reflection happens when sound waves disappear upon hitting a surface.

• The reflection of sound occurs when sound waves hit a surface and bounce back.

Give an example of an application of sound in daily life.

• Car horn

• Doorbell

• Whistle

• Alarm clock

How does the pitch of a sound change with an increase in frequency?

• The pitch of a sound increases with an increase in frequency.

• The pitch of a sound decreases with an increase in frequency.

• The pitch of a sound remains constant with an increase in frequency.

• The pitch of a sound is not affected by frequency changes.

What is the formula to calculate the speed of sound in a medium?

• speed = frequency + wavelength

• speed = frequency / wavelength

• speed = amplitude x wavelength

• speed = frequency x wavelength

How does the speed of sound change with a change in temperature?

• The speed of sound increases with an increase in temperature.

• The speed of sound decreases with a decrease in temperature.

• The speed of sound remains constant regardless of temperature.

• The speed of sound decreases with an increase in temperature.

Describe an experiment to demonstrate the reflection of sound.

• Set up a sound source and receiver with a sound-reflecting surface in between. Emit a sound wave towards the surface and measure the time delay for the reflected sound to reach the receiver.

• Measure the time delay for the sound to reach the receiver without any reflecting surface

• Use a transparent surface for sound reflection

• Place the sound source and receiver next to each other without any reflecting surface