SP5 Light and the Electromagnetic Spectrum

Question 1

Define the law of reflection

Answer 1

the angle of incidence = the angle of reflection

Question 2

Define total internal reflection (TIR)

Answer 2

the complete reflection of a light ray reaching a boundary greater than the critical angle

Question 3

Define specular reflection

Answer 3

when waves are reflected in a single direction by a smooth surface eg. light reflected by a mirror

Question 4

Define diffuse reflection

Answer 4

when waves are reflected by a rough surface and the waves are reflected in all directions

Question 5

What is white light?

Answer 5

A mixture of all the different colours of light, which all have different wavelengths

Question 6

Why do we see different colours?

Answer 6

All colours are absorbed, apart from the colour you see, which is reflected

An apple looks red because all wavelengths are absorbed, but the red wavelength is reflected

Question 7

How do colour filters work?

Answer 7

Colour filters are used to filter out different wavelengths of light, so that only certain colours are transmitted. A blue filter transmits blue light, and absorbs all the others

Question 8

Define focal length

Answer 8

is the power of the lens. The more powerful the lens, the more strongly it converges rays of light, so the shorter the focal length

Question 9

Define the principle of focus (F)

Answer 9

Convex lens = where rays hit the lens parallel to the axis meet
Concave lens = where rays hitting the lens parallel to the axis appear to all come from

(the meeting point of rays)

Question 10

Define convex / converging lens

Answer 10

bulges outwards in the middle causing parallel rays of light to be brought together at the principal focus

Question 11

Define concave / diverging lens

Answer 11

caves inwards causing parallel rays of light to spread out

Question 12

Define a real image

Answer 12

formed when the light rays actually come together to form the image - this image can be captured on a screen as the light rays meet at the place where the image seems to be

Question 13

Define a virtual image

Answer 13

formed when the light rays from the object appear to be coming from a completely different place to where they’re actually coming from. They don’t form point where the image seems to be so it can not be captured on a screen

Question 14

Properties of EM waves

Answer 14

• They all travel at the same speed through a vacuum (space)

- They’re all vibrations of electric and magnetic fields

Question 15

Describe the transfer of energy by EM waves

Answer 15

EM waves transfer energy from a source to an absorber. The higher the frequency of the EM wave, the more energy it transfers

Question 16

What can our eyes detect?

Answer 16

Visible light = red, orange, yellow, green, blue, indigo, violet

Question 17

What causes EM waves?

Answer 17

A variety of changes in atoms and their nuclei giving a large range of frequencies

Question 18

How are the EM waves grouped on the spectrum?

Answer 18

based on their wavelength and frequency

long wavelength = low frequency
short wavelength = high frequency

Question 19

Ways that the EM spectrum is absorbed and transmitted

Answer 19

All objects are continually radiating and absorbing EM radiation

Question 20

Ways that the EM spectrum is refracted and reflected

Answer 20

radio waves, microwaves, infrared waves, visible light and ultraviolet waves, can be reflected and refracted when they travel at different velocities in different substances

Question 21

Define radio waves and its uses

Answer 21

• Long wave radio can be received even if the receiver isn’t in the line of sight of the trasnmitter
• Bluetooth sends data over short distances without wires
• TV and FM radio uses very short wavelengths, and you must be in direct sight of the transmitter

Question 22

Define microwaves and its uses

Answer 22

• Communication to and from satellites as the EM waves can pass through the Earth’s watery atmosphere
• In microwave ovens, the microwaves are absorbed by water molecules in food, causing water to heat up, and therefore transfers heat energy to the rest of the food

Question 23

Define infrared and its uses

Answer 23

• Used to transfer information
• Infrared cameras detect infrared radiation and monitor temperature - thermal imaging
• Infrared sensors can be used in security systems
• Electric heaters

Question 24

Define visible light and its uses

Answer 24

• Photographic film reacts to light to form an image - this is how traditional cameras create photographs
• Digital cameras image sensors, which detect visible light

Question 25

Dangers of EM waves based on frequency

Answer 25

Higher frequencies = transfer more energy = more possible harm

Question 26

Harmful effects of Microwaves and Infrared

Answer 26

Microwaves can be absorbed causing heating of cells, which may be dangerous. Infrared and visible light are mostly reflected or absorbed by the skin, causing some heating too. IR can cause burns if the skin gets too hot

Question 27

Harmful effects of Ultraviolet

Answer 27

Is absorbed by skin. Has a higher frequency so is potentially more dangerous. It’s a type of ionising radiation and when absorbed can damage cells on the surface of your skin, which can lead to skin cancer. Can damage eyes and cause blindness

Question 28

Harmful effects of X-Rays and Gamma Rays

Answer 28

They are ionising, so they can cause mutations and damage cells too, which can lead to cancer. They have higher frequencies, so transfer more energy and even more damage. They pass through skin and are absorbed by deeper tissues

Question 29

How are long wavelengths EM affected by different substances?

Answer 29

Longer EM wavelengths can’t penetrate through as many different substances as they have lower frequency and therefore lower energy

Question 30

How are radio waves produced and detected by electrical circuits?

Answer 30

Radio waves can be produced by using an alternating current in an electrical current. The object in which charges oscillate to create the radio waves is called a transmitter.

Question 31

How is the intensity of emitted radiation dependant on the temperature of the body?

Look in rev guide page 44

Answer 31

Intensity is the power per unit area (power is energy transferred per second)

The intensity increases more rapidly for shorter wavelengths than longer wavelengths. As temp increases, the intensity of emitted wavelengths increases

Question 32

Explain that power radiated and absorbed must be the same to maintain a constant body temp

Answer 32

If more power is being absorbed than released, the body temp. will continually increase as it is taking in more energy. Absorption and radiation must be balanced to keep a consistent temp.

Question 33

What happens to body temp. if power radiated and absorbed is not equal?

Answer 33

Body temp. will either increase or decrease as the body is taking in or giving out too much thermal energy

Question 34

Factors affecting the energy absorbed and radiated by Earth

Answer 34

Radiation is reflected and absorbed by the Earth’s atmosphere, clouds and surface.

Question 35

How do factors affect the temperature of the Earth?

Answer 35

Most of this radiation is absorbed, therefore the temperature increases

Question 36

Define ultraviolet and its uses

Answer 36

• Fluorescence is a property of certain chemicals, where UV is absorbed and visible light is emitted
• Fluorescent lights are used for lights for long periods
• Security pens can be used to mark property and under UV light will glow
• Bank notes and passports have special markings shown under UV to detect forgeries

Question 37

Define X-rays and its uses

Answer 37

• View internal structure of objects and materials

-

Question 38

Define X-rays and its uses

Answer 38

• View internal structure of objects and materials

- Radiographers in hospitals take X-rays to help doctors diagnose broken bones

Question 39

Define gamma rays and its uses

Answer 39

• Used to sterilise medical instruments and kill microbes
• Food can be sterilised this way too
• Can detect cancer and used in treatments for cancer