Lesson 9: Properties of EM waves

Question 1

What 4 different things can happen when an electromagnetic wave hits a boundary between two different medias?

Answer 1

• The substance may:
• Absorb the wave
• Transmitt the wave
• Refract the wave
• Reflect the wave

Question 2

What does the amount of absorption, transission, reflection and refraction of a wave depend on (once it has hit a different material?)

Answer 2

• This depends on the wavelength of the wave that is hitting the material.

Question 3

What happens to the speed of a light ray when it enters a glass block?

Answer 3

• The light ray decreases in speed.
• ## This causes the direction of the wave to change (when the wave is travelling through the glass block itself.)

Question 4

What happens to the speed of a light ray that has entered a glass block and is now leaving the glass block?

Answer 4

• When the ray entered the glass block it would’ve slowed down.
• When the ray leaves the glass block, it speeds up (so the ray changes direction again.)

Question 5

What is the one instance where a wave will not be refracted (at a boundary between two different medias?)

Answer 5

• The one instance the wave won’t refract is if the waves enter or leave the medium (ie. a glass block) at right angles.
• The direction of the wave will remain the same.

Question 6

What can radio waves be produced by?

Answer 6

• Radio waves can be produced by oscillations (of electrons) in electrical circuits.

Question 7

What happens when radio waves are absorbed ie. by an electric ciruit in an aerial?

Answer 7

• Induces electron oscillations (creating an alternate current.)
• The alternate current has the same frequency as the radio wave itself.

Question 8

What is “radiation dose?”

Answer 8

• Radiation dose is a measure of the risk of harm resulting from an exposure of the body to radiation.

Question 9

What is a big issue with UV rays?

Answer 9

• UV waves cause skin to age prematurely/ increases risk of skin cancer.

Question 10

What is the issue with X- rays and gamma rays?

Answer 10

• X- rays/ Gamma rays are ionsing radiation that can cause the mutation of genes/ cancer.

Question 11

What does the effect that X- rays, gamma rays and UV waves have on the human body dependent on?

Answer 11

• The type of radiation (from these 3.)
• The dose you are revieving from that radiation.

Question 12

What is 1 sievert equal to in milisieverts?

Answer 12

1000 millisieverts (mSv) = 1 sievert (Sv)

Question 13

What are the 2 ways electromagnetic waves can be absorbed/ generated?

Answer 13

1.) Changes in atoms (ie. electrons changing energy levels.)
2.) Changes in the nuclei (ie. gamma rays being emitted due to changes in nucleus of atom - nucleus = unstable)

Question 14

True or False

Only CERTAIN electromagnetic waves can be absorbed/ emitted due to changes in atoms and nuclei.

Answer 14

• False.
• Electromagnetic waves will be generated/ absorbed over a large frequency range (from radio rays to gamma rays.)

Question 15

Wavefronts entering a glass block.
Explain, in terms of wave-fronts, why refraction happens at boundary between air and glass.

Answer 15

• Different parts of the wave-front enter the glass at different times.
• The velocity/ speed (of the wave-fronts) is less in the glass.
• One part of the wave-front changes speed before the other parts.