6.2. Waves - Reflection, EM waves, refraction

Question 1

what three things can happen when a wave arrives at a boundary between two different materials

Answer 1

1. absorbed
2. transmitted
3. reflected

Question 2

how is a wave absorbed

Answer 2

the waves are absorbed by the material the wave is trying to cross into, this transfers energy to the material’s energy stores

Question 3

how is a wave transmitted

Answer 3

the waves carry on travelling through the new material, often leading to refraction

Question 4

relationship between angle of incidence and angle of reflection

Answer 4

angle of incidence = angle of reflection

Question 5

what is the angle of incidence

Answer 5

the angle between the incoming wave and the normal

Question 6

what is the angle of reflection

Answer 6

the angle between the reflected wave and the normal

Question 7

what is the normal

Answer 7

an imaginary line perpendicular to the surface at the point of incidence (the point where the wave hits the boundary)

Question 8

how to draw the normal

Answer 8

dotted line

Question 9

what is a specular reflection

Answer 9

happens when a wave is reflected in a single direction by a smooth surface. e.g. when light is reflected by a mirror you get a nice clear reflection

Question 10

what is a diffuse reflection

Answer 10

when a wave is reflected by a rough surface e.g. a piece of paper and the reflected rays are scattered in different directions

Question 11

why do diffuse reflections happen

Answer 11

when the normal is different for each incoming ray, which means the angle of incidence is different for each ray. rule of angle of incidence = angle of reflection still applies

Question 12

what happens when light is reflected by a rough surface

Answer 12

when light is reflected by a rough surface, the surface appears matte (not shiny) and you don’t get a clear reflection of objects

Question 13

how are electromagnetic waves able to travel through vacuums

Answer 13

EM waves aren’t vibrations of particles, they’re vibrations of electric and magnetic fields. therefore, they can travel through a vacuum

Question 14

what are EM waves

Answer 14

transverse waves that transfer energy from a source to an absorber. e.g. a hot object transfers energy by emitting infrared radiation, which is absorbed by the surrounding air

Question 15

what happens to the speed of EM waves in air and vacuums

Answer 15

they travel at the same speed through air and vacuums

Question 16

what are the seven basic types of EM waves - in increasing frequency/decreasing wavelength

Answer 16

radiowaves
microwaves
infrared
visible light
ultra violet
X-rays
gamma rays

Question 17

what is refraction

Answer 17

when a wave crosses a boundary between materials at an angle and it changes direction

Question 18

what is how much a wave is refracted depend on

Answer 18

on how much the wave speeds up or slows down, which usually depends on the density of the two materials. (usually the higher the density of a material, the slower a wave travels through it)

Question 19

what happens when a wave crosses a boundary and slows down

Answer 19

it will bend towards the normal

Question 20

what happens when a wave crosses a boundary and speeds up

Answer 20

it will bend away from the normal

Question 21

what happens to the wavelength and the frequency of a wave when its refracted

Answer 21

the wavelength changes
the frequency stays the same

Question 22

what happens when a wave crosses a boundary but it travelling along the normal

Answer 22

it will change speed, but it’s not refracted

Question 23

what is the optical density of a material

Answer 23

a measure of how quickly light can travel through it - the higher the optical density, the slower light waves travel through it

Question 24

how to use transparent materials to investigate refraction

Answer 24

1. place a transparent rectangular block on a piece of paper and trace around it. use a laser to shine a ray of light at the middle of one side of the block
2. trace the incidence ray and mark where the light imerges on the other side of the block. remove the block, and, with a straight line, join up the incidence ray and the emerging point to show the path of the refracted ray through the block
3. draw the normal at the point where the light ray entered the block. use a protractor to measure the angle between the incident ray and the normal (angle of incidence), and the angle between the refracted ray and the normal (angle of refraction)
4. repeat this experiment using rectangular blocks made from different materials, keeping the incident angle the same throughout

Question 25

how to investigate different materials reflecting light by different amounts

Answer 25

1. take a piece of paper and draw a straight line across it. place an object so one of its sides lines up with this line 2. shine a ray of light at the object's surface and trace the incoming and reflected light beams 3. draw the normal at the point where the ray hits the object. use a protractor to measure the angle of incidence and the angle of reflection and record these values in a table. also make a note of the width and brightness of the reflected light ray 4. repeat experiment for a range of objects

Question 26

what do smooth surfaces like mirrors reflect

Answer 26

clear reflections, the reflected ray is as thin and bright as the incident ray

Question 27

what do rough surfaces like paper reflect

Answer 27

cause diffuse reflection which causes the reflected beam to be wider and dimmer (or not observant at all)

Question 28

what do the wave fronts being closer together show

Answer 28

a change in wavelength (and so a change in velocity)

Question 29

what do the wave fronts changing direction show

Answer 29

the wave has hit a different medium at an angle, so the wave changes direction