Topic 5 - Light And The Electromagnetic Spectrum

Question 1

What is a ray diagram?

Answer 1

A way of modelling what happens when light is reflected or refracted.

Question 2

What is the Law of Reflection?

Answer 2

When waves are reflected, the angle of reflection is equal to the angle of incidence.

Question 3

What is total internal reflection?

Answer 3

Most light passes through interface but a little is reflected.
As the angle of incidence increases, the angle of refraction also increases until the refracted light passes along the interface.
If the angle of incidence increases further, the light is completely reflected inside the glass.

The angle of incidence at which this starts to happen is called the critical angle.

Question 4

What is the core practical for investigating refraction?

Answer 4

1) Place a piece of plain paper on the desk. Set up a power supply , Ray box and single slit so that you can shine a single ray of light across the paper on your desk.
2) Place a rectangular glass block on the paper and draw around block.
3) Shine a ray of light into your block. Use small crosses to mark where the rays of lights go.
4) Take the block off the paper. Use the ruler to join the crosses to show the path of the light, and extend the lines so they meet the outline of the block. Join points where the light entered and left the block to show where it travelled inside the block.
5) Measure the angles of incidence and reflection where the light entered the block and measure the angles where it left the block.
6) Repeats steps 3 and 5 wth the ray entering the block at different angles.
7) Move the ray box so that the light ray reaches the interface at right angles. Note what happens to the light as it enters and leaves the block.

Question 5

What is diffuse reflection?

Answer 5

Most materials have rough surfaces if you examine them closely, so the reflected light is scattered in all directions.

Question 6

What is speculation reflection?

Answer 6

Very smooth surfaces i.e. mirrors, reflect the light evenly.

Question 7

What happens when white light hits a coloured surface?

Answer 7

Some of the colours that make the surface up are absorbed and some are reflected.
A yellow object looks yellow because it reflects yellow light and absorbs all the other colours. A white object looks white because it reflects all of the colours.

Question 8

What are filters?

Answer 8

Filters are pieces of transparent material that absorb some of the colours in white light.
For example, a blue filter transmits(allows through) blue light and absorbs all other colours.

Question 9

What is a lens?

Answer 9

Piece of transparent material shaped to refract light in particular ways.
The power of a lens describes how much it bends light that passes through it.
A powerful lens is one that is more curved and bends the light more.

Question 10

What is a converging lens?

Answer 10

A converging lens is fatter in the middle than at the edges. It makes parallel rays of light converge (come together) at the focal point.

Question 11

What is a focal length?

Answer 11

The distance between the focal point and the centre of lens

Question 12

What is a diverging lens?

Answer 12

Thinner in the middle than at the edges. The focal point is the point from which the rays seem to be coming after passing through lens. (Focal point in front of lens and rays go out)

Question 13

What is a real image?

Answer 13

An image that can be projected onto a screen by a converging lens used to focus rays of lights onto a screen.

I.e. Light is reflected from the object in all directions but only three rays are needed to show how image forms

Question 14

What is a virtual image?

Answer 14

An object close to a converging lens that cannot be projected onto a screen.
The image appears to be on the same side of the lens as the object, and is upright and magnified.

Question 15

What do diverging lenses always produce with a virtual image?

Answer 15

Virtual images that are the same way up,much smaller and closer to the lens than the object.

Question 16

What are electromagnetic waves ?

Answer 16

Waves that all travel at the same speed in a vacuum and are all transverse.

Question 17

What are ultra violet waves?

Answer 17

Electromagnetic waves with frequencies a little higher than visible light

Question 18

What are infrared waves?

Answer 18

Electromagnetic waves with frequencies slightly lower than visible light.

All objects emit energy by infrared radiation. The hotter the object, the more energy it emits
Feel it when energy is transferred from the sun to our skin e.t.c

Question 19

Who first investigated Infrared radiation?

Answer 19

William Herschel put dark coloured filters on his telescope to help him observe the sun safely.
He noticed different coloured filters heated up his telescope to different extents and he wondered whether different colours of light contained different amounts of heat.

He used a prism to split sunlight into a spectrum and put a thermometer in each of the colours in turn.

Question 20

What are the seven colours in the visible spectrum?

Answer 20

Red, orange, yellow, green, blue, indigo, violet aka ROY G BIV

Question 21

What is the electromagnetic spectrum?

Answer 21

Highest frequency Longest wavelength
Shortest wavelength Lowest frequency

Gamma X-rays Ultra Visible Infrared Micro Radio
Rays Violet Light Waves Waves

Question 22

How are telescopes used for electromagnetic waves?

Answer 22

Use curved mirrors to focus the electromagnetic radiation onto a central sensor.
The type of material used for the mirror and the size of the telescope depends on the wavelength of the radiation being studied

Question 23

Why do they use telescopes?

Answer 23

Starts and other space objects can emit energy at all wavelengths.
Astronomers use telescopes to study this radiation but they need to use different kinds of telescope to study different wavelengths.
Because different materials affect electromagnetic waves depending on the wavelength.

Question 24

What are some uses for visible light?

Answer 24

Eyes can detect it

Light bulbs e.t.c

Question 25

What are some uses for infrared radiation?

Answer 25

Used for communication at short ranges e.g computers in same room or TV and remote control.
A grill or toaster transfers energy to food by infrared radiation.
Security systems usually have sensors that can detect intruders using infrared radiation

Question 26

What are some uses for microwaves?

Answer 26

Used for communications and satellite transmissions

Also used in phone signals, microwave oven and microwaves to heat up food.

Question 27

What are some uses for radio waves?

Answer 27

Used for transmitting radio broadcasts and TV programmes

Question 28

What are radio waves produced by?

Answer 28

Oscillations in electrical circuits
A metal rod or wire can be used as an aerial to receive radio waves.
The radio waves are absorbed by the metal and cause oscillations in electrical circuits connected to the aerial.

Question 29

How do waves travel?

Answer 29

Travel in straight lines unless they are refracted or reflected.
If radio waves reach the ionosphere, they may be refracted back to Earth.

Microwaves are not refracted in the Earths atmosphere.

Question 30

What happens to the wavelengths when temperature increases?

Answer 30

Wavelengths get shorter

Question 31

How does the Earth’s energy balance?

Answer 31

Earth’s surface absorbs about half of the radiation that reaches it from the sun.
It re-admits this energy as infrared radiation, which can warm up the atmosphere.
For the temperature to stay the same, it must radiate energy into space at the same average rate its absorbed.

Question 32

What is the greenhouse effect?

Answer 32

Some gases in our atmosphere e.g. Carbon dioxide naturally absorb some energy, keeping the earth at a higher temperature than if there were no atmospheres.

Question 33

What is the method for the Core Practical : Investigating Radiation?

Answer 33

1) Cover four or more boiling tubes in different coloured materials I.e. black card and foil
2) Pour the same volume of hot water from a kettle into each tube
3) Insert a bung with a thermometer into each tube. Measure the temperature of the water in each tube and start a stop clock.
4) Record the temperature of the water in each tube every 2 minutes for 20minutes.

Question 34

What are some uses for ultra violet waves?

Answer 34

Uses more energy than visible light so it can be used to disinfect water by killing micro organisms in it.
Some materials absorb UV rays and re-emit visible light. This is fluorescence.
These materials are normally used in security markings.
UV rays can help see forged notes because they don’t emit white light
Many low energy bulbs use fluorescent lamps.

Question 35

What are some uses for x-rays?

Answer 35

X-rays can pass through materials visible light can’t.
E.g. pass through fat and muscles but bone absorbs x-rays.
This means x-rays can be used in medicine to make images of the inside of the body.
Also be used to examine inside of metal objects and inspect luggage.

Question 36

What are some uses for gamma rays?

Answer 36

Can kills cells i.e. sterilise food and surgical equipment as it kills harmful micro organisms.
Can be used to kill cancer cells in radiotherapy and used to detect cancer cells.
A chemical that emits gamma rays is injected into the blood. The chemical is designed to collect inside cancer cells.
A scanner outside body then locates the cancer by finding source of gamma rays.

Question 37

What is a danger of microwaves?

Answer 37

Can heat water and because our bodies are mostly fluid, it could be quite harmful.

Question 38

What is a danger of infrared radiation?

Answer 38

Our skin absorbs infrared radiation that we feel as heat.

So too much infrared radiation can damage or destroy cells causing burns to our skin.

Question 39

What are some dangers of ultra violet radiation?

Answer 39

UV rays can cause sunburn and damage DNA.
Too much exposure to UV rays can lead to skin cancer.
Help protect our skin by covering up with coats and hats, wearing sun cream with a Huge SPF factor.
Can also damage eyes, especially those is snowy mountains and snow reflects UV rays.

Question 40

How are x-rays and gamma rays dangerous?

Answer 40

High frequency than UV rays so transmit more energy.
Can penetrate the body.
Excessive exposure to x-rays and gamma rays may cause mutations in DNA that can kill cells or cause cancer.