Light

Question 1

Reflection of Light

Answer 1

○ When light bounces off a reflection
○ Specular reflection
§ When light bounces off a smooth and shiny surface
§ The light will reflect at the same angle as it hits the surface
□ Angle of incidence = angle of reflection
○ Diffuse reflection
§ When light hits a rough object and reflects in lots of different directions

Question 2

Angles

Answer 2

§ Angle of incidence
□ The angle at which light hits a reflecting surface
§ Angle of reflection
□ The angle at which light bounces off a reflecting surface

Question 3

Light reflecting off curved mirrors

Answer 3

• Concave mirror
• Convex mirror

Question 4

Concave mirror

Answer 4

□ Light rays travel through a straight line towards the mirror are reflected inwards
- Meet at focal point
□ Make things seem lighter
- Useful for applying makeup

Question 5

Convex mirror

Answer 5

□ Light rays travelling in a straight line towards the mirror are reflected outwards
□ Give a wider field of vision
- Useful in rear view mirrors in cars
- Mirrors in corners

Question 6

Absorption

Answer 6

□ A light ray might be absorbed rather than bouncing off an object’s surface

Question 7

Speed of light

Answer 7

§ Speed of light as being 3 x 108 m/s in a vacuum
§ If light travels through a medium, it travels slower
§ The speed of light is different for each medium light travels through but it is always slower than the speed of light in a vacuum
§ For example, the speed of light in water is only 2.25 x 108 m/s

Question 8

Refraction

Answer 8

§ Light always travels through air at the same speed in a straight line
§ When light travels from air into water or glass (matter with a different density), it slows down slightly and changes direction
§ The bending of light as it passes from one material into another is called refraction
§ When the light changes medium and slows down, it will bend towards the normal
§ When the light changes medium and speeds up, it will bend away from the normal

Question 9

Refraction and wavelength

Answer 9

§ Frequency constant
§ Speed changes - wavelength of light must change
□ As the speed decreases, the wavelength also decreases
□ As the speed increases, the wavelength also increases

Question 10

Lenses

Answer 10

§ A curved piece of transparent glass or plastic that refracts light
§ Light rays striking different parts of a curved surface change direction by different amounts
§ Depending on the on the shape of the lens, the light either
□ Gets further apart, or diverges
□ Gets closer, or converges

Question 11

Concave lenses

Answer 11

□ Lens that is curved inwards, and is thinner in the middle
□ Cause parallel light rays to diverge, or spread out
□ Focal point
- The rays diverge and appear to an observer to come from one point
□ Focal length
- The distance from the focal point to the centre of the lens

Question 12

Convex lenses

Answer 12

§ Convex lenses
□ Lens that is curved outwards, and is thicker in the middle
□ Cause parallel light rays to converge, or get closer
□ Focal point
- Where the parallel rays converge
□ Focal length
- The distance between the focal point and the centre of the lens