Light and electromagnetic waves

Question 1

what is the law of reflection

Answer 1

Angle of incidence (i) = Angle of reflection (r)

Question 2

why do lights rays undergo a change in direction

Answer 2

because the light changes speed

Question 3

what does the change in direction depend on

Answer 3

From less dense to more dense (e.g air to glass), light bends towards the normal

From more dense to less dense (e.g. glass to air), light bends away from the normal

Question 4

what properties change during refraction

Answer 4

speed and wavelength – the frequency of waves does not change

Question 5

what colour has the highest frequency

Answer 5

red has a low frequency, whilst blue has a high frequency

When light refracts, it does not change colour (think of a pencil in a glass of water), therefore, the frequency does not change

Question 6

what is total internal reflection

Answer 6

The angle of incidence is greater than the critical angle and the incident material is denser than the second material

Question 7

what is the critical angle

Answer 7

As the angle of incidence is increased, the angle of refraction also increases until it gets closer to 90°
When the angle of refraction is exactly 90° the light is refracted along the boundary
At this point, the angle of incidence is known as the critical angle θc

Question 8

what are the conditions for the TIR

Answer 8

The angle of incidence > the critical angle (i > θc)

The incident material is denser than the second material

Question 9

what is specular reflection

Answer 9

reflection from a smooth surface in a single direction

Question 10

what is diffuse reflection

Answer 10

Reflection from a rough surface causes scattering, this is what gives objects a dull or matt appearance

Question 11

what is absorption of colour

Answer 11

Energy is transferred from the wave into the particles of a substance

Question 12

what are colour filters

Answer 12

Colour filters work by absorbing certain wavelengths and transmitting other wavelengths
These certain wavelengths correspond to certain colours

Question 13

what happens when white light hits a red filter

Answer 13

Red light is transmitted

All the other colours are absorbed

Question 14

what is a principal focus

Answer 14

parallel rays of light are brought to a focus

Question 15

what is a focal length

Answer 15

The distance from the lens to the principal focus is called the focal length

Question 16

what does focal length depend on

Answer 16

This depends on how curved the lens is

The more curved the lens, the shorter the focal length

Question 17

what does the power of a lens depend on

Answer 17

The focal length of the lens

The shape of the lens

Question 18

how is power changed

Answer 18

The more curved the lens, the shorter the focal length

The shorter the focal length, the greater the power of the lens

Question 19

what 3 thins should you look for when describing a image

Answer 19

Real or virtual
Magnified (larger) or diminished (smaller)
Upright or inverted

Question 20

how a real images presented on converging lens ray diagram

Answer 20

If an object is placed further from the lens than the focal length f then a real image will be formed

Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line

Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f

The image is the line drawn from the axis to the point where the above two rays meet

Question 21

how a real images presented on converging lens ray diagram

Answer 21

If an object is placed further from the lens than the focal length f then a real image will be formed

Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line

Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f

The image is the line drawn from the axis to the point where the above two rays meet

Question 22

how are virtual images presented on converging lens

Answer 22

If the object is placed closer to the lens than the focal length f then a virtual image will be formed

Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line

Draw a dashed line continuing this ray upwards

Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly through the principal focus f

Also, draw a dashed line continuing this ray upwards

The image is the line drawn from the axis to the point where the two dashed lines meet

Question 23

what type of image is created on a diverging lens

Answer 23

virtual image

Question 24

diverging lens presenting virtual lens

Answer 24

Start by drawing a ray going from the top of the object through the centre of the lens. This ray will continue to travel in a straight line

Next draw a ray going from the top of the object, travelling parallel to the axis to the lens. When this ray emerges from the lens it will travel directly upwards away from the axis

Draw a dashed line continuing this ray downwards to the focal point, f

The image is the line drawn from the axis to the point where the above two rays meet