Waves (electromagnetic, lenses, light and black body radiation)

Question 1

What electromagnetic waves and their features?

Answer 1

transverse waves that transfer energy from the source of the waves to an absorber

• all electromagnetic waves travel at the same velocity (the speed of light) in the air or a vacuum

Question 2

order the different types of electromagnetic waves from the lowest to the highest frequency?

Answer 2

radio, microwaves, infrared, visible, ultraviolet, x-rays, Gamma

Question 3

How are signals created?

Answer 3

radio waves can be produced by oscillations in electrical circuits

when radio waves are absorbed, they cause electrons in the circuit to oscillate

this creates an alternating current with the same frequency as radio waves - this is how the signal is received

Question 4

what happens when electromagnetic waves are being generated or absorbed?

Answer 4

changes in atoms and the nuclear of atoms occur

Question 5

How can waves be generated?

Answer 5

by electrons moving between energy levels, as a result, of heat or electrical excitation can generate waves

i.e. an unstable nucleus can give out excess energy as gamma rays

Question 6

Why are ultraviolet waves, x-rays and gamma rays harmful?

Answer 6

because they transfer a lot of energy

Question 7

What damages could UV waves cause?

Answer 7

• cause the skin to age prematurely
• increase the risk of skin cancer
• Can damage the retina of the eye

Question 8

What damages can X-rays and gamma rays cause?

Answer 8

damage cells by ionising atoms and if absorbed by the nucleus o the cell. can cause gene mutations and cancer

Gamma rays can also cause cells to mutate and if they affect sex cells or a developing embryo, the effects are seen in the next generation.

Question 9

What are the units of radiation dose and what does it measure?

Answer 9

sieverts ad is a measure of the risk of harm resulting from an exposure of the body to radiation

Question 10

What is the speed of light?

Answer 10

3.00 × 10^8 ms–1

Question 11

What are the uses of radio waves and why?

Answer 11

• television, radio and Bluetooth

this is because radio waves are low energy waves and therefore, not harmful, making them ideal for radio transmissions

are able to be reflected from the ionosphere = allows us to send radio waves very long distances around the Earth

able to travel long distances without being absorbed by buildings or trees

longer wavelength radio waves can also spread out between hills

Question 12

What are the uses of micro waves and why?

Answer 12

• Satellite communications, cooking food

Microwaves travel in straight lines through the atmosphere, can pass through without being reflected or refracted = good for transmitting signals to satellites in orbit and transmitting them back down to receivers

for heating food, water molecules in food absorb the energy from microwaves, which causes the temperature of the food to increase

Question 13

What are the uses of infrared waves and why?

Answer 13

• Electrical heaters, cooking food, infrared camera
• energy of infrared is easily absorbed by the surface of objects
• electrical heaters etc glow red hot as the electricity flows through them

Question 14

What are the uses of visible waves and why?

Answer 14

• Fibre optic communications
• visible light travels down optical fibres from one end to the other without being lost through the sides
• has a short wavelength, can carry a lot of information ( fire optics used to carry telephone and cable TV signals)

Question 15

What are the uses of UV waves?

Answer 15

Causes some things to fluoresce – (e.g. washing powders in clothes so are often used at clubs and parties).

Security marking.

Can kill microbes so can be used to sterilise medical equipment.

Insect control (UV attracts insects).

Question 16

What are the uses of X-rays waves and why?

Answer 16

Medical imaging and treatments

• X-rays are able to penetrate soft tissue but not bone. A photographic plate behind a person will show shadows where bones are

Question 17

What are the uses of Gamma waves and why?

Answer 17

Medical imaging, tracer, Sterlising food, treatment of tumours,

• Gamma rays are the most energetic = used to destroy bacteria and tumours
• gamma emitting source is injected into the patient and its progress is followed around the body. gamma can pass out of the body

Question 18

What is a convex lens?

What happens in a convex lens?

Answer 18

lens that curves outwards

rays of light are brought to a focus at the principal focus.

Question 19

What is the focal length?

Answer 19

The distance from the lens to the principal focus

Question 20

Why doesn’t the middle ray get refracted?

Answer 20

because it is normally incident onto its surface

Question 21

What is a concave lens?

What happens in a concave lens?

Answer 21

lens that curve inwards

parallel rays of light entering the lens spread out, this makes the rays of light appear to have come from the principal focus on the same side of the lens they have originated

Question 22

What type of images do convex lenses?

What type of images do concave lenses?

Answer 22

real or virtual

only virtual

Question 23

What is a real image?

Answer 23

on the opposite side of the lens to the object can be projected onto a screen

lens come together

Question 24

What is a virtual image?

Answer 24

on the same side as the object and can only be seen by looking through the lens

lens dont come together

Question 25

equation for magnification

Answer 25

image height/ object height

Question 26

How to make a lens more powerful?

Answer 26

• making the focal length more shorter
• make the lens more curved
• use different material that naturally refract light strongly

Question 27

What happens to the image when an object is more than 2 focal lengths from the convex lens?

Answer 27

• image is diminished
• inverted
• the image is real

Question 28

What happens to the image when an object is between 1-2 focal lengths from the convex lens?

Answer 28

• magnified
• inverted
• real

Question 29

describe what happens to light when it passes through a lens

Answer 29

it refracts :

the light bends towards the normal when it passes into the lens

then away when it passes out of the lens

Question 30

What happens to the image when an object is reflected by a concave lens?

Answer 30

• diminished
• right way up
• virtual ( rays do not meet at the principal focus)

Question 31

What happens to the image when an object is closer to the lens than the focal length for a convex lens?

Answer 31

• virtual image
• magnified
• right way up

this is why convex lenses are used as magnifying glasses

Question 32

What damage could microaves cause?

Answer 32

Tissues can be damaged if too much microwave radiation is absorbed by living tissues so protective (reflective) suits must be worn if working near a powerful transmitter. They can also cause cataracts in the eye.