Light and Sound

Question 1

Unit for angles

Answer 1

Degree (°)

Question 2

Unit for frequency

Answer 2

Hertz (Hz)

Question 3

Unit for length

Answer 3

Metre (m)

Question 4

Unit for speed/velocity

Answer 4

Metre/second (m/s)

Question 5

Unit for time

Answer 5

Second (s)

Question 6

What type of waves are light waves and what can they do?

Answer 6

Transverse waves and the can all be reflected and refracted

Question 7

What is the law of reflection?

Answer 7

The angle of incidence = the angle of reflection

Question 8

What happens when images are reflected in a plane mirror?

Answer 8

They are laterally inverted
Images are upright
Same size of the object
The image is virtual

Question 9

What is a diffuse reflection?

Answer 9

When light hits an uneven surface (like paper) light reflects at different angles

Question 10

What is the normal?

Answer 10

Imaginary line that’s perpendicular to the surface at the point of incidence

Question 11

What is the angle of incidence?

Answer 11

Angle between the incoming wave and the normal

Question 12

What is the angle of refraction?

Answer 12

Angle between reflected wave and the normal

Question 13

How do waves travel through objects of different densities?

Answer 13

EM waves travel slower in denser media (usually)
Sound waves travel faster in denser media

Question 14

What is refraction?

Answer 14

The change of wave speed as light travels between media of different optical densities

Question 15

What is refractive index?

Answer 15

Is the measure of change of wave speed in a material

Question 16

What is the speed of light in a vacuum?

Answer 16

3x10^8 m/s

Question 17

How to calculate the refractive index (using refractive index, speed of light in a vacuum and speed in a medium)?

Answer 17

Refractive index = speed of light in a vacuum/ speed of light in a medium
n = c/v

Question 18

Does refractive index have a unit?

Answer 18

Refractive index is dimensionless (no unit)

Question 19

What is snells law?

Answer 19

n1sinθ1=n2sinθ2

Question 20

How to calculate refractive index (using refractive index, sin(i), sin(r)?

Answer 20

Refractive index = sin(i)/ sin(r)

Question 21

Investigate the refraction of light, using rectangular blocks, semi-circular
blocks and triangular prisms:

Answer 21

Draw around the block on piece of paper and draw normal on the block
Using a ray block shine the light into the normal at the angle required
Draw where the emergent ray comes out of the block

Question 22

What is dispersion?

Answer 22

It’s the splitting of white light into component colours

Question 23

Investigate the refractive index of glass, using a glass block:

Answer 23

Draw around glass block and draw the normal
Mark out different angles for the incident ray
Then use a ray box and shine line at the different angles and mark emergent ray
Remove block and draw refracted ray (in the box)
Measure ‘i’ and ‘r’ from the normal
Plot a graph sin(i) against sin(r), straight line, gradient gives refractive index

Question 24

How could you improve this “investigate the refractive index of glass, using a glass block” experiment?

Answer 24

Repeat experiment and average the results
Turn off lights in the room

Question 25

What is TIR?

Answer 25

When light is reflected internally so no light comes out of the object

Question 26

What does θc equal?

Answer 26

The critical angle

Question 27

What is the critical angle?

Answer 27

It’s the angle of incidence when the angle of refraction 90°

Question 28

Why do we use semicircular glass?

Answer 28

So the light is incident perpendicularly and doesn’t bend along it’s path

Question 29

What is the calculation for the critical angle using snells law?

Answer 29

Critical angle = 1/refractive index
sinθc = 1/n

Question 30

What is the most common application of TIR?

Answer 30

Fibre optic cables

Question 31

What are fibre optic cables made of?

Answer 31

Plastic or glass with central core surrounded by cladding

Question 32

Why is the core of fibre optic narrow?

Answer 32

So narrow light signals passing always hit the core-cladding so it’s TIR.

Question 33

What is the refractive index of air?

Answer 33

1

Question 34

How does TIR work with prisms?

Answer 34

The ray of light travels into one prism where it’s TIR at 90, the light travels to another prism where the light is TIR at 90°, this allows us to see an object (periscope)

Question 35

What type of waves are sound waves and what can they do?

Answer 35

Longitudinal and it can be reflected and refracted

Question 36

What is the frequency range for human hearing?

Answer 36

20-20,000Hz

Question 37

How would you investigate the speed of sound in air?

Answer 37

Using a oscilloscope, two microphone to find the wavelength of sounds
Start with two microphones next to the speaker, move one away until two waves are aligned on the display which are one wavelength apart
Measure distance between the microphones
Use the formula v = f x λ

Question 38

What is the frequency of ultrasound?

Answer 38

Above 20,000Hz

Question 39

What are the applications of ultrasound?

Answer 39

Foetal monitoring
Checking welds

Question 40

What is the screen of an oscilloscope divided into?

Answer 40

1cm x1cm squares

Question 41

What is the y-axis of an oscilloscope called?

Answer 41

The (voltage) gain or V/cm

Question 42

What is the a-axis of an oscilloscope called?

Answer 42

The time base

Question 43

What is the time base?

Answer 43

The time taken for the trace to cover 1 square

Question 44

What is the time base set to on an oscilloscope?

Answer 44

5 Milliseconds (0.005s)

Question 45

How does the amplitude of the wave correlate to the amplitude?

Answer 45

The greater the amplitude the more energy it carries, this means it will be louder

Question 46

What does frequency mean?

Answer 46

The number of complete vibrations each second

Question 47

What does the higher the frequency mean for vibrations

Answer 47

The higher frequency means more complete vibrations per second