Sound (Class 8 Science)

Understand the properties of sound, how it travels, and why it matters. Learn about frequency, wavelength, and practical applications of sound.

Sound (Class 8 Science)

Understand the properties of sound, how it travels, and why it matters. Learn about frequency, wavelength, and practical applications of sound.

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TL;DR: Understand the properties of sound, how it travels, and why it matters. Learn about frequency, wavelength, and practical applications of sound.

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Understand the properties of sound, how it travels, and why it matters. Learn about frequency, wavelength, and practical applications of sound.

Sound MCQs with Answers & Explanations

Q1. What is sound?

  1. Movement of particles
  2. Mechanical waves that require a medium ✓ (correct)
  3. Light waves
  4. Electromagnetic radiation

Explanation: Sound is a mechanical wave that travels through a medium like air, water, or solids. It is produced by vibrating objects.

Q2. Can sound travel in a vacuum?

  1. Only at high speed
  2. Only at low speed
  3. No ✓ (correct)
  4. Yes

Explanation: Sound cannot travel in a vacuum because it requires a medium to propagate. Without molecules to vibrate, sound waves cannot be transmitted.

Q3. What is the speed of sound in air at room temperature?

  1. 300,000 km/s
  2. 1000 km/h
  3. 100 m/s
  4. 340 m/s ✓ (correct)

Explanation: The speed of sound in air at 20 degrees Celsius is approximately 340 m/s or 1224 km/h. It varies with temperature and medium.

Q4. What is frequency in sound waves?

  1. Number of vibrations per second ✓ (correct)
  2. Speed of sound
  3. Distance between waves
  4. Loudness of sound

Explanation: Frequency is the number of complete vibrations or oscillations per second, measured in Hertz (Hz). Higher frequency means higher pitch.

Q5. What is wavelength?

  1. Time taken for one vibration
  2. Distance between two consecutive crests or troughs ✓ (correct)
  3. Speed of the wave
  4. Frequency of the wave

Explanation: Wavelength is the distance between two consecutive crests (or troughs) of a wave. It is inversely related to frequency.

Q6. How is pitch related to frequency?

  1. No relationship
  2. Pitch is independent of frequency
  3. Pitch increases with frequency ✓ (correct)
  4. Pitch decreases with frequency

Explanation: Pitch is the perception of frequency. Higher frequency sounds have higher pitch; lower frequency sounds have lower pitch.

Q7. What is loudness related to?

  1. Frequency
  2. Wavelength
  3. Speed of sound
  4. Amplitude of the wave ✓ (correct)

Explanation: Loudness is determined by the amplitude of sound waves. Greater amplitude means louder sound, measured in decibels (dB).

Q8. What is echo?

  1. Reflection of sound from a surface ✓ (correct)
  2. Duplication of sound
  3. High-pitched sound
  4. Repetition of a word

Explanation: Echo is the reflection of sound from a surface back to the listener. It occurs when sound bounces off hard surfaces like walls or mountains.

Q9. What is the range of human hearing?

  1. 10-20,000 Hz
  2. 20-20,000 Hz ✓ (correct)
  3. 0-10 Hz
  4. 100-50,000 Hz

Explanation: Human ears can typically hear sounds between 20 Hz and 20,000 Hz (20 kHz). Below 20 Hz are infrasonic waves; above 20,000 Hz are ultrasonic waves.

Q10. What is the relationship between speed, frequency, and wavelength?

  1. Speed = frequency / wavelength
  2. Speed = frequency - wavelength
  3. Speed = frequency x wavelength ✓ (correct)
  4. Speed = frequency + wavelength

Explanation: The fundamental wave equation is: Speed = Frequency x Wavelength. This relationship applies to all waves including sound.

Frequently Asked Questions

Why does sound travel faster in water than in air?

Water molecules are closer together and more densely packed than air molecules. This allows vibrations to transfer more efficiently, making sound travel faster in water (~1500 m/s) than in air (~340 m/s).

What are some uses of sound waves beyond hearing?

Ultrasonic waves are used in medical ultrasound, sonar for navigation, and cleaning. Infrasonic waves occur in nature through earthquakes and elephant communication.

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