SP5 Light and the Electromagnetic Spectrum

Question 1

What are ray diagrams?

Answer 1

way of modelling what happens when light is relfected or refracted

Question 2

What is the normal?

Answer 2

line drawn at a right angle to barrier or mirror in a ray diagram. angles of i & r are always measured from nromal

Question 3

What is the angle of incidence?

Answer 3

angle between an incoming light ray and the normal

Question 4

What is the angle or refraction/reflection?

Answer 4

angle between the normal and ray of light thats been reflected/refracted

Question 5

What is the law of reflection?

Answer 5

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

i = r

Question 6

What is total internal reflection?

Answer 6

the reflection of a ray of light inside a mdeium such as glass or water when it reaches an interface.
can only happen when A of I inside the material is greater than the critical angle.

critical angle = the A of I at which TIR starts to happen

Question 7

What is diffuse reflection?

Answer 7

when materials with rough surfaces reflect light and it scatters in all directions

Question 8

What is specular reflection?

Answer 8

when materials with smooth surfaces reflect light evenly

Question 9

How can we split up white light into the colours of the visible spectrum (ROYGBIV)?

Answer 9

using a prism

Question 10

Why does an object look a cetain colour, e.g. yellow?

Answer 10

the objects reflects yellow light and absorbs all the other colours

Question 11

Why does a white object look white?

Answer 11

because it reflects all of the colours

Question 12

How can we turn white light into coloured light?

Answer 12

using a filter - a transparent material that absorbs some of the colours in white light

e.g. blue filter transmits blue light and absorbs all other colours

Question 13

What is a converging lens?

Answer 13

aka a convex lens

bulges outwards in the middle, causes parallel rays of light to be bought together (converge) at the focal point. the focal point of a converging lens is where rays hitting the lens parallel to the axis all meet

Question 14

What is a diverging lens?

Answer 14

aka a concave lens

caves inwards, causes parallel rays of light to spread out (diverge). focal point of diverging lens is the point where rays hitting the lens parallel to the axis appear to all come from. they meet up at a point behind the lens.

Question 15

What is visible light?

Answer 15

the frequencies of light that our eyes can detect

Question 16

What are electromagnetic waves?

Answer 16

waves that are transverse
in a vacuum, they travel at 3 x 10^8 m/s
they vary in wavelength

Question 17

What are ultraviolet waves?

Answer 17

EM waves with frequencies higher than visible light

Question 18

What are infrared waves?

Answer 18

EM waves with frequencies lower than visible light

Question 19

What do all objects omit energy by?

Answer 19

IR radiation

Question 20

What did William Herschel do?

Answer 20

split sunlight into a spectrum and noticed that different colours of light contained different ‘amounts of heat’

Question 21

What is the electromagnetic spectrum?

Answer 21

the full range of electromagnetic waves

increasing frequency, decreasing wavelength:
radio waves
micro waves
infrared
visible light
ultraviolet
x rays
gamma rays

Question 22

What are the uses of visible light?

Answer 22

light bulbs emit it
cameras detect and record it

Question 23

What are the uses of infrared?

Answer 23

communication (computers and TV remotes)
optical fibres
grill/toaster for cooking (food absorbs radiation and heats up)
thermal images
security systems with sensors to detect IR from intruders

Question 24

What are the uses of micro waves?

Answer 24

communications
satellite transmissions
mobile phone signals
microwave ovens (transfer energy to food, heats up)

Question 25

What are the uses of radio waves?

Answer 25

transmitting radio boradcasts/Tv programmes
communications sent via satellites
communication with spacecraft from controllers on ground

Question 26

How do radio waves work?

Answer 26

produced by oscillations in electrical circuits

a metal rod can be used as an aerial to receive them.
radio waves are absorbed by the metal and cause oscillations in electrical circuits connected to the aerial

some frequencies of radio waves can be refracted by a layer in the atmosphere called the ionosphere. if they reach it at a good angle, they may be refracted enough to be sent back to earth

Question 27

What must a system do to stay at a constant temperature?

Answer 27

absorb the same amount of power as it radiates

Question 28

What is the greenhouse effect and how does it work?

Answer 28

the arths surface absorbs about half of the radiation that reaches it from the sun. it re-radiates this as infrared raditation which can warm up the atmosphere

some gases in our atmosphere naturally absorb some energy, keeping the earth at a higher temperature than if there were no atmsophere. if some greenhouse gases were removed from the atmoshpere, it would be able to hold less energy and its temp would decrease.

Question 29

What are the uses of ultraviolet?

Answer 29

used in fluorescent lamps
security pens - invisble ink
bank notes and passports
sterilise water - kills bacteria in water, making it safe to drink

Question 30

What are the uses of x rays?

Answer 30

view internal structures of bodies
x ray images in hospitals
airport security scanners

Question 31

What are the uses of gamma rays?

Answer 31

sterilise medical instruments
sterilise foods
medical imaging tracers - to detect cnacer
cancer treatment

Question 32

What are the dangers of EM waves?

Answer 32

higher frequency of EM wave = more energy it transfers = potentially more dangerous to humans

some wavelengths of microwaves can be absorbed, which would cause heating of cells = dangerous

IR and visible light can cause heating when absorbed by skin. IR can burn skin

UV absorbed by skin. could lead to skin cancer or blindness

xrays and gamma rays can cause mutations and damage cells. can be asborbed by deeper tissues in body.