LIGHT, INFRARED, MICROWAVES, AND RADIO WAVES

Question 1

what is white light?

Answer 1

light from ordinary lamps and from the Sun

Question 2

why is it called the white light?

Answer 2

it has all the colours of the visible spectrum in it

Question 3

what happens to the wavelength of the spectrum?

Answer 3

it increases as you go from violet to red

Question 4

what do photographers need to know?

Answer 4

how shades and colours of light affect the photographs they take

Question 5

how does light impact a film camera?

Answer 5

the light is focused by the camera lens on to a light-sensitive film
-the film then needs to be developed to see the image of the objects that were photographed

Question 6

how does light affect a digital camera/mobile phone camera?

Answer 6

the light is focused by the lens on to a sensor, which is made up of thousands of tiny light-sensitive cells called pixels

• each of them give a dot image, which can be seen on a small screen at the back of a camera
• when a photograph is taken the image is stored electronically on a memory card

Question 7

what do all objects emit?

Answer 7

infrared radiation

Question 8

the hotter an object is

Answer 8

the more infrared radiation it emits

Question 9

what is infrared radiation absorbed by?

Answer 9

your skin which can damage, burn or kill skin cells as it heats up the cells

Question 10

why do optical fibres in communication systems use infrared radiation instead of visible light?

Answer 10

infrared radiation is absorbed less than visible light in the glass fibres

Question 11

why do remote control handsets for Tv and video equipment transmit signals carried by infrared radiation?

Answer 11

when you press a button on the handset it sends out a sequence of infrared impulses
-it’s used because suitable infrared impulses can easily be produced and detected electronically

Question 12

why are infrared scanners used in medicine?

Answer 12

to detect infrared radiation emitted from hot spots on the body surface as it means the tissue underneath is unhealthy

Question 13

why are infrared cameras used?

Answer 13

to see people and animals in the dark

Question 14

infrared radiation is used to heat up objects quickly?

Answer 14

• electric heaters that emit infrared radiation warm rooms quickly
• electric cookers that have halogen hobs heat up food faster than ordinary hobs as they’re designed to emit much more infrared radiation than ordinary hobs

Question 15

microwaves have a shorter

Answer 15

wavelength than radio waves

Question 16

the spectrum of visible light covers only

Answer 16

a very small part of the electromagnetic spectrum

Question 17

why do people use microwaves for communications (satellite TV )?

Answer 17

they can pass through the atmosphere and reach satellites above the Earth
-they can also carry mobile phone signals

Question 18

why do microwave ovens heat food faster than ordinary ovens?

Answer 18

microwaves can penetrate into food and are absorbed by the water molecules in the food, heating it

• the oven itself doesn’t absorb microwaves as it doesn’t contain any water molecules
• it doesn’t become hot like the food

Question 19

why do people use microwaves for communications (satellite TV )?

Answer 19

they can pass through the atmosphere and reach satellites above the Earth
-they can also carry mobile phone signals

Question 20

what are the frequencies of radio waves?

Answer 20

from about 300 000 Hz to 3000 million Hz (where microwave frequencies start)

Question 21

why are radio waves used?

Answer 21

to carry radio, TV, and mobile phone signals

Question 22

why can microwaves and radio waves be hazardous?

Answer 22

they penetrate people’s bodies and can heat internal parts of the body

Question 23

how else do people incorporate radio waves in their daily lives?

Answer 23

it can be used instead of cables to connect a computer to other devices (printer/computer mouse)
-Bluetooth-enabled devices can communicate with each other over a range of about 10 m without the need of cables

Question 24

what is mobile phone radiation?

Answer 24

it’s microwave radiation and is also radio waves at near-microwave frequencies

Question 25

absorption and emission of infrared radiation:

Answer 25

compare emissions from 2 different surfaces(light and shiny / dark and matte) and measure how fast twos cans of hot water cool

• to compare absorption by 2 different surfaces measure how fast the two cans containing cold water heat up when placed in sunlight for the same time
• both cans contain same amount of water
• at the start of the test the volume and temp of the water in each can needs to be the same
• thermometer to measure water temp at intervals as it cools
• take care with hot water