Waves

Question 1

Differences between transverse and longitudinal waves?

Answer 1

Transverse waves have peaks and troughs whereas longitudinal waves have compressions and rarefactions

Oscillations in transverse waves are perpendicular to the direction of energy transfer whereas oscillations in longitudinal waves are parallel to the direction of energy transfer

Transverse waves (light waves) can travel in a vacuum whereas longitudinal waves (sound waves) can’t.

Question 2

Similarities in all electromagnetic waves?

Answer 2

They all travel at 3x10^8 m/s in a vacuum and they are all transverse waves

Question 3

Order of the electromagnetic spectrum?

Answer 3

RW, MW, IR, VL, UV, XR, GM
with wavelength decreasing from left to right
with frequency increasing from left to right

Question 4

Why doesn’t the refractive index have no unit?

Answer 4

The units on numerator and denominator cancel out and refractive index is only a ratio

Question 5

What can be deduced from the orbit of the moon

Answer 5

• the moon is oval in shape
• the moon is furthest away from the earth at the middle of the month
  -the orbit of the moon changes monthly

Question 6

Suggest uses and dangers for any 3 electromagnetic waves

Answer 6

Uses
MW: Can be used for heating food
GR: Can be used to sterilise medical equipment
XR: Can be used to view internal human body structure

Dangers
MW: They can cause internal heating of cell tissues
GR: They can cause cell mutations leading to cancer
XR: They can cause cell mutations leading to cancer

Question 7

Under white fur, polar bears have black skin, how do these colours affect the heat energy lost by the polar bear’s body?

Answer 7

Black is a good absorber and emitter of heat and as heat is reflected off of the white fur, it is absorbed by the black skin keeping the bear warm

Question 8

Suggest why the radiation doesn’t pass down to the polar bear’s skin

Answer 8

The UV rays travel in the air and not in materials hence, the UV rays get absorbed by the hair.

Question 9

In what cases does light get totally internally reflected?

Answer 9

• If the angle of incidence is greater than the critical angle considering the critical angle doesn’t change
• Light goes from more dense to a less dense medium

Question 10

In what cases does the ray of light get refracted towards the normal?

Answer 10

As the light goes from a less dense material to a more dense material, it gets refracted inwards considering refraction occurs due to the change in wavelength

Question 11

Difference between DC and AC?

Answer 11

DC current travels in a single direction whereas AC current switches direction frequently

Question 12

Difference between light waves and sound waves

Answer 12

Sound waves are transverse, light waves are longitudinal
Light waves can travel in a vacuum, sound waves can’t

Question 13

Harmful effect of infra red waves

Answer 13

Not internal heating of body tissue because that’s microwaves but SKIN BURNS

Question 14

Describe how to measure frequency of sound waves using oscilloscopes

Answer 14

• Connect microphone to oscilloscope
• Adjust oscilloscope to get steady trace
• adjust time base to get at least 1 complete cycle
• count number of squares for a number of complete cycles
• multiply number of squares by the time base to find the time period
• use f=1/T

Question 15

What happens to the light ray as it goes from a less dense medium to a more dense medium?

Answer 15

Light gets refracted and slows down

Question 16

What happens when angle of refraction is greater than critical angle and why

Answer 16

Total Internal Reflection as the ray travels from a high to a low refractive index

Question 17

What happens to the wavelength of water as it goes from a less dense medium into a more dense medium

Answer 17

• Wavespeed decreases and frequency remains constant

Question 18

How to calculate critical angle when given angle of incidence?

Answer 18

90 - angle of incidence

Question 19

what is the wavelength on a wave?

Answer 19

• The length from one peak to another peak

Question 20

Light wave travels from more dense to less dense medium. What happens?

Answer 20

• Light ray gets refracted away from the normal
• Wavespeed increases whilst frequency remains constant

Question 21

When temperature decreases, how does it affect wavelength?

Answer 21

• Wavelength decreases
• as speed of sound decreases

Question 22

Why is using a graph to find the refractive index a better method than simply calculating it using a pair of angles from a table

Answer 22

• The value relates to all the data collected
• Effects of errors can be reduced

Question 23

define critical angle

Answer 23

where the angle of refraction is equal to 90* and the light is refracted along the boundary