II. SHORT ANSWER TYPE QUESTIONS

1. How is sound produced? Why is there a difference in the voice of adults and children?

• Sound is produced when an object vibrates and creates disturbances in a medium (air, water, etc.).
• The difference in voice between adults and children is due to the length and thickness of the vocal cords. Adults have longer and thicker vocal cords, producing deeper voices, while children have shorter and thinner cords, producing higher-pitched voices.

2. What is amplitude of vibration? How is amplitude related to loudness?

• Amplitude is the maximum displacement of vibrating particles from their mean position.
• Greater amplitude = louder sound; smaller amplitude = softer sound.

3. Give two uses of ultrasonic sound.

• Used in medical imaging (ultrasound scanning).
• Used in SONAR (Sound Navigation and Ranging) to detect underwater objects.

4. What is the audible range of human ear?

• 20 Hz to 20,000 Hz.

5. A bat screams with a sound more than 20,000 Hz but we cannot hear it. Why?

• Because humans cannot hear sound frequencies above 20,000 Hz. Such sounds are called ultrasonic sounds.

6. What are the characteristics of sound?

• Pitch (depends on frequency).
• Loudness (depends on amplitude).
• Quality/Timbre (depends on waveform).

7. If the frequency of an oscillator is 25 Hz, what would be its time period?

• Formula: Time Period (T) = 1 / Frequency (f)
• T = 1 / 25 = 0.04 seconds.

III. LONG ANSWER TYPE QUESTIONS

1. How is sound produced in human beings?

• In humans, sound is produced by the voice box (larynx).
• Vocal cords inside the larynx vibrate when air passes through them, producing sound.

2. How do we hear sound? Explain.

• Sound waves enter the outer ear and travel through the ear canal.
• They strike the eardrum, causing it to vibrate.
• These vibrations pass through the three tiny bones (hammer, anvil, stirrup).
• Vibrations reach the cochlea (inner ear), where they are converted into electrical signals.
• The auditory nerve carries these signals to the brain, and we hear sound.

3. What is the difference between noise and music?

• Noise: Unpleasant, irregular, and unwanted sound (e.g., traffic sound).
• Music: Pleasant and regular sound (e.g., musical instruments).

4. List some measures to reduce noise pollution.

• Plant more trees.
• Use silencers in vehicles and machines.
• Avoid using loudspeakers at night.
• Use soundproof materials in buildings.
• Follow noise control rules near schools and hospitals.

5. How would you show that sound needs a medium to propagate?

• Take an electric bell in a glass jar.
• When air is present, we can hear the bell.
• If air is pumped out (vacuum created), the sound becomes faint and finally stops.
• This proves sound cannot travel in vacuum; it needs a medium (air, water, solids).

IV. HIGHER ORDER THINKING SKILLS

1. How do trees control noise pollution?

• Trees act as natural barriers.
• Their leaves, branches, and trunks absorb and deflect sound waves.
• Dense plantations can reduce noise pollution in cities.