Samacheer Class 9 Science - Sound

• (a) stretched strings
• (b) stretched membranes
• (c) air columns
• (d) metal plates

Answer:
(d) metal plates

• (a) only if no moisture is present
• (b) if particles move from one place to another
• (c) if both particles and disturbance move
• (d) if disturbance moves

Answer:
(d) if disturbance moves

Particles vibrate about mean position; disturbance travels.

• (a) wax
• (b) vacuum
• (c) water
• (d) empty vessel

Answer:
(b) vacuum

Sound cannot travel through vacuum.

• (a) sea water
• (b) ground glass
• (c) dry air
• (d) human blood

Answer:
(b) ground glass

Sound travels faster through iron than through water. The speed of sound is maximum in solids because the particles in solids are very closely packed together, allowing vibrations to be transmitted more rapidly from one particle to the next. In solids, the inter-atomic distances are smallest, resulting in stronger intermolecular forces that facilitate faster propagation of sound waves. Water, being a liquid, has particles that are less tightly bound compared to solids, so sound travels more slowly through it. The speed of sound in iron is approximately 5000 m/s, while in water it is approximately 1500 m/s.

Answer:

Frequency.

Definition:

Frequency is number of vibrations produced in one second.

Unit:

Answer:

Speed greater than speed of sound in air is called supersonic speed.

(approximately at room temperature)

Answer:

• Vibrating object sets nearby particles vibrating.
• Vibrating particles transfer energy to neighbouring particles.
• Compressions and rarefactions travel through medium.
• Sound finally reaches ears.

No, sound cannot be heard on the Moon. The reason is that the Moon has no atmosphere, meaning there is no material medium present for sound waves to travel through. Sound is a mechanical wave that requires a medium such as air, water, or solid material to propagate. Sound waves travel by causing particles in the medium to vibrate and transfer energy from one particle to the next. Since the Moon's surface is in a vacuum with no air or other gaseous medium, sound waves cannot be generated or transmitted. Therefore, even if an astronaut were to shout on the Moon, the sound would not travel and could not be heard by another person, though they could communicate through radio equipment that uses electromagnetic waves, which do not require a material medium.

Compression

When vibrating body moves forward:

• particles crowd together
• pressure increases

This region is called:

Compression

Rarefaction

When vibrating body moves backward:

• particles spread apart
• pressure decreases

This region is called:

Rarefaction

Cleaning

Used to remove tiny dust particles from delicate objects.

Industry

Used to detect cracks in metal blocks.

Medicine

(i) Echocardiography

Ultrasound used to study heart.

(ii) Kidney Stones

Ultrasonic waves break stones into smaller pieces.

SONAR

Working

• Ultrasonic waves transmitted through water.
• Waves strike object and reflect back.
• Detector receives echo.
• Time interval measured.

Distance:

Where:

• (d) = distance
• (v) = speed of sound
• (t) = total time

This method is called:

Echo-ranging

Given:

Frequency means vibrations per second.

In one minute:

Answer:

Correction made:
Unit should be “vibrations”, not “Hz”.