Light and Sound Waves

Question 1

How is the property of reflection used in periscopes?

Answer 1

An incident ray hits a plane mirror at an angle of 45⁰ and is reflected at 45⁰ and so are turned through an angle of 90⁰

At the second mirror, the incident ray hits a plane mirror at an angle of 45⁰ and is reflected at 45⁰ and so is again turned through an angle of 90⁰

Question 2

What is the speed of light in glass?

Answer 2

2 x 10⁸ m/s

Question 3

The speed of light is fastest in:

(a) air
(b) glass
(c) water

Answer 3

AIR

Question 4

Rules of refraction:

Answer 4

Less dense ➡ denser: Light slows down and is bent towards the normal

Vice versa

Question 5

When is there no refraction when light rays pass through different media?

Answer 5

When it strikes the boundary between the two media at 90⁰

Question 6

Where is the property of refraction used?

Answer 6

Used in microscopes, telescopes, and cameras using lenses

Question 7

Define refractive index:

Answer 7

A measure of the change in the speed of a wave as it travels across the boundary between two media.

Also describes how much the direction of the wave changes

Question 8

The formula for refractive index:

Answer 8

n = sin (i) / sin (r)

Question 9

What is the angle of refraction when angle of incidence is equal to the critical angle

Answer 9

90⁰

Question 10

What is the critical angle?

Answer 10

The largest possible value for the angle of incidence at which light is refracted at 90⁰

Question 11

When does TIR occur?

Answer 11

When the angle of incidence is greater than the critical angle, light is reflected at the boundary

Question 12

The critical angle:

(a) from glass to air
(b) from water to air

Answer 12

(a) 42⁰

(b) 49⁰

Question 13

The formula for critical angle:

Answer 13

sin c = 1/n

Question 14

What is the advantage of prisms over mirrors?

Answer 14

Images produced by prisms are often brighter and clearer than those produced by mirrors

Question 15

Uses of TIR:

Answer 15

• Prismatic periscope (submarines)
• Bicycle and car reflectors
• Prismatic binoculars
• Optical fibres
• Endoscope (keyhole surgery)

Question 16

Advantage of optical fibres:

Answer 16

Less energy is lost

Question 17

How is information transmitted via optical fibres?

Answer 17

Electrical signals (telephone) ➡ lasers ➡ pulses of light ➡ optical fibres ➡ light-sensitive detectors: pulses ➡ electrical signals (earpiece)

Question 18

Why do binoculars have prisms?

Answer 18

To obtain large magnification of objects and would otherwise look like telescopes

Question 19

Speed of sound in air

*It can vary due to temperature

Answer 19

340 m/s

Question 20

SONAR full form:

What is it?

Where is it used?

Answer 20

Sound, Navigation And Ranging

Method of using sound waves to detect objects and measure their distance

Used for echo sounding

Question 21

Effect of temperature on the speed of sound?

Answer 21

Higher temperature: faster sound

Question 22

How is pitch determined?

Answer 22

Higher frequencies produce high-pitched sounds

Question 23

How is loudness determined?

Answer 23

Larger amplitude results in louder sounds

Question 24

The audible range for humans:

Answer 24

20 Hz to 20000 Hz

Question 25

Explain the Doppler Effect

Answer 25

A ————————————————– B

Stationary: Wavefronts are evenly spaced
: A and B hear sound of the same frequency
and wavelength

Moving ahead: Wavefronts at B are compressed
: B hears sound of shorter wavelength
and higher frequency (pitch) and vice
versa

Question 26

What is the Doppler Effect?

Answer 26

A change in frequency due to the relative movement of the source of waves/ observer