EM Spectrum

Question 0

Uses of gamma rays?

Answer 0

Sterilising medical equipment - kills microbes and don’t need to boil stuff because high temps could damage some instruments

Sterilises food - kills microbes and keeps food fresh for longer without having to freeze it (food not radioactive after)

Question 1

What characteristic of one electromagnetic wave makes it different from another electromagnetic wave?

Answer 1

They vary in wavelength and frequency

Question 2

Uses of X-rays?

Answer 2

X- radiography to observe the internal structure of objects, including human bodies.

• X-ray radiation is directed through object onto white detector plate. X-rays pass through flesh but not denser material eg bone or metal so leave white image where skeleton is.

Question 3

Uses of Ultraviolet

Answer 3

Fluorescent lamps/lights use UV radiation to emit visible light. Nearly all the UV radiation is absorbed by a phosphor coating on the inside of the glass which emits visible light instead.

More energy efficient than filament lights bulbs so used in places where they’ll be needed for long periods (school/office)

Question 4

Uses of visible light?

Answer 4

• Photography - cameras use a lens to focus visible light onto a light-sensitive film/electronic sensor

Lens aperture - controls how much light enters camera

Shutter speed - determines how long film/sensor is exposed to light

Vary these ^ or sensitivity of film/sensor, photographer can capture as much light/little as they want

• seeing and communication using optical fibres that bounce waves off the sides of a very narrow core.

Question 5

Uses of Infra-red (IR)?

Answer 5

Heaters and cookers

night vision- IR radiation given out by objects can be detected by night vision equipment in darkness. Things that wouldn’t normally be seen are displayed on a screen as a picture.

Question 6

Uses of microwaves?

Answer 6

Mobile phones - calls travel as microwaves to nearest transmitter

satellite communication - signal from transmitter is transmitted into space and picked up by satellite reviewer dish orbiting above the earth. Satellite transmits signal back to earth and received by satellite dish on ground.

Microwave oven - microwaves absorbed by water molecules in food. Penetrate a few cm into food and then is absorbed and conducted/convected to other parts of the food

Question 7

Uses of radio waves

Answer 7

Long-wave radio - transmitted half way around the world. Diffract around curved surface of world, even around hills, tunnels…

Short-wave radio - transmitted out of the earth and reflected from the ionosphere (electrically charged layer in the Earth’s upper atmosphere)

Question 8

From high to low frequency.

Answer 8

Gamma rays, X-rays, ultraviolet, visible light, Infra-red (IR), microwaves, radio waves

Question 9

4 similarities that all parts of the EM spectrum share?

Answer 9

They all transfer energy

They are all transverse waves

They all travel at the speed of light in a vacuum (300 million m/s)

They can all be reflected, refracted and diffracted

Question 10

Effects of being exposed to radio waves?

Answer 10

Long time exposure can cause leukaemia.

Question 11

Effects of being exposed to microwaves?

Answer 11

Internal heating of body tissue, absorbed by water molecules. Microwave ovens need shielding to prevent microwaves from reaching user.

Question 12

Effects of being exposed to infra-red?

Answer 12

Can make surface molecules vibrate, heating them. If exposed to too much - cause skin burns.

Protect yourself with insulating materials to reduce amount of IR reaching skin.

Question 13

Effects of being exposed to ultraviolet?

Answer 13

Damage surface cells, over exposure can cause blindness.

Ionising - knock electrons off atoms, cause cell mutation or damage cells - cancer

Skin blistering/ skin cancer/ sun burn

Protection - wear sunscreen with UV filters whenever in the sun. stay out of strong sunlight to protect skin from UV radiation.

Question 14

Effects of being exposed to visible light?

Answer 14

Over exposure can make you blind

Question 15

Effects of being exposed to gamma rays?

Answer 15

High frequency, ionising (penetrate further into body) cell mutation, destruction, tissue damage, cancer.

Radioactive sources of gamma rays should be kept in lead lined boxes when not in use, short exposure.

Question 16

Advantages of digital over analogue?

Answer 16

Both weaken as they travel so need to be amplified along their route. They also pick up noise from other signals or electrical disturbances. When analogue signals are amplified, the noise is also amplified so the signal loses quality.

However a regenerator circuit creates an accurate, clean copy of the original digital signal without amplifying any accompanying noise. w digital, the noise is ignored and signal remains high

Question 17

What does a regenerator circuit do?

Answer 17

Regenerator circuit reduces noise from a digital signal and creates an accurate, clean copy of the original digital signal without amplifying any accompanying noise.

Question 18

What is the relationship between the physical quantities wave speed, wavelength and frequency?

Answer 18

Wave speed = frequency x wavelength

v = f x λ
m/s Hz m

Question 19

What are the differences between analogue and digital signals?

Answer 19

An analogue signal can take any value within a certain range. The amplitude and frequency of an analogue wave can vary continuously

A digital signal can only take two values; 1 or 0 or on/off

Question 20

Why can digital signals carry more information?

Answer 20

A digital signal can carry more information than an analogue signal. Because it has a larger bandwidth (range of frequencies)

➡️Quantisation is the process of ‘rounding’ multiple values in a signal to a smaller set. This means more information can be packed into a smaller space. Digital signals only have two values so quantisation doesn’t lose much information but with analogue, lots of information is lost when a continuous range is rounded off.