Core Physics – Energy

L/O :- To Know the order of the electromagnetic waves within the spectrum

“Does light have a

family?”

Exam Date -

Quick Quiz - What do you remember from last lesson?

• Draw and label a wave• What is the law of reflection?• What is the equation for working out the

speed of a wave?• What happens to a light ray when it

travels from air through glass? Why does this happen?

• What is diffraction?• What are the 2 different types of wave?

Give an example• How do you work out the pay-back time

for insulation?• What are the pros and cons of wind

energy?• Where are step-up transformers used?• How does increasing the volume of a

sound affect the wave?

Light does have a family – It is related to all the other waves in the electromagnetic spectrum

They are related because they are all transverse wave and they all travel at the same speed

through a vacuum

Can you work out what type of wave all these pictures represent?

What do you think they all have in common with light?

The speed of light is 299,792,458m/s but usually we round this up to

300,000,000m/s

The speed of light was first measured in the 1600’s – How do you think this was

done?

Galileo was one of the first to try. He sent an assistant up to a neighbouring hill and flashed a light. The assistant flashed a light when he could see Galileo’s light and Galileo timed the response.

However, the light was too quick for this experiment

In the 1970’s, a Danish astronomer Ole Roemer was observing Jupiter’s moon Io, and noticed that sometimes it appeared to be in the wrong place, either a little bit ahead or behind. He also noticed that this was when the earth was slightly closer or further away from Jupiter. He realised that the light was taking less time to get to him when the earth was closer so that is why he was seeing it in the wrong place. He used difference in the distance between the earth and Jupiter to work out the speed of light – CLEVER!!!

The speed of light is 299,792,458m/s but usually we round this up to

300,000,000m/s

How long does it take the light from the sun to get to the earth?

How many times can it travel around the earth in a

second?

Earth’s circumference = 40,076km

300,000,000 ÷ 40,000,000 = 7

Distance from sun to earth 149,600,000,000m

150,000,000,000 ÷ 300,000,000 = 498s (8 mins)

The Electromagnetic Spectrum

Gamma rays

X-rays Ultra violet Visible light

Infra red Microwaves

Radio/TV

Each type of radiation shown in the electromagnetic spectrum has a different wavelength and a different frequency:

Each of these types travels at the same speed through a _______ (300,000,000m/s), and different wavelengths are absorbed by different surfaces (e.g. infra red is absorbed very well by ___________ surfaces). This absorption may heat the material up (like infra red and _______) or cause an alternating current (like in a __ _______).

Words – black, microwaves, long, short, TV aerial, vacuum

High frequency, _____ wavelength

Low frequency, _____ (high) wavelength

γ

Task - To research each of the waves in the

electromagnetic spectrum

You should answer these questions

• What are the waves used for?• Are there any dangers?

• You may find this a useful place to start http://www.darvill.clara.net/emag/index.htm

Type of radiation Uses Dangers

Gamma rays

X rays

Ultra violet

Visible light

Infra red

Microwaves

TV/radio

Treating cancer, sterilisation

Medical

Sun beds

Seeing things

Remote controls, heat transfer

Satellites, phones

Communications

Cell mutation

Cell mutation

Skin cancer

None (unless you look at the sun)

Sunburn

Few

Very few

What have you learnt?

• Do you know what all electromagnetic waves have in common?

• Can you list the electromagnetic spectrum from the shortest wavelength to the longest?

• Can you list the electromagnetic spectrum from the longest wavelength to the shortest?

• Can you give a use of each part of the electromagnetic spectrum

• Do you know which parts of the electromagnetic spectrum are the most dangerous?