Topic 3.2 - Light

Question 1

What happens when rays of light hit a plane mirror?

Answer 1

They are reflected.

Question 2

What are the characteristics of an image formed from a plane mirror?

Answer 2

• The same size as the object
• On the the same side of the mirror as the object
• An inverted (upside down) version of the object

Question 3

When light is reflected how do angles i and r compare?

Answer 3

angle of incidence = angle of reflection

Question 4

How are the angles of incidence and reflection measured?

Answer 4

Relative to the normal.

Question 5

What is a virtual image?

Answer 5

An image produced on the same side of the lens as the object.

Question 6

What is a real image?

Answer 6

• An image produced on the opposite side of the lens from the object.
• A real image can be formed on a screen as the light rays cross after the lens.

Question 7

What kind of image is produced by a plane mirror?

Answer 7

A virtual image.

Question 8

What is refraction?

Answer 8

• Refraction is the change in speed of a wave crossing a boundary between two media, resulting in a change in direction.

Question 9

Which property of a wave is not changed by refraction?

Answer 9

The frequency

Question 10

What is the critical angle?

Answer 10

The angle of incidence which produces an angle of refraction of 90°

Question 11

What is internal reflection?

Answer 11

When light rays reaches a boundary and some of the rays are reflected back into the medium which it came from.

Question 12

What is total internal reflection?

Answer 12

When a ray of light is fully reflected back into the medium it came from, when reaching a boundary between media.

Question 13

When does total internal reflection occur?

Answer 13

When the angle of incidence is greater than the critical angle.

Question 14

Define refractive index

Answer 14

The ratio of the speed of light in a vacuum to the speed of light in any given medium.

Question 15

Give the equations for refractive index

Answer 15

Question 16

When light passes through a converging lens…

Answer 16

The light rays bend towards the normal, and meet at a focal point.

Question 17

What is the principal focus of the lens?

Answer 17

A focal point before a convex lens, from wich light rays appear to come from, or the focal poiny afdter a concave lens where all the rays meet.

Question 18

Draw a diagram of light rays through a converging lens

Answer 18

Question 19

How can lenses act as magnifying glasses?

Answer 19

By producing an enlarged, virtual image.

Question 20

How does wavelength affect refraction?

Answer 20

Shorter wavelength waves refract more

Question 21

What happens when white light is shone through a prism?

Answer 21

It separates into a spectrum of all its coloured light components.

Question 22

Why is white light separated by a prism?

Answer 22

Each different coloured light wave has a different wavelength. The shorter wavelength lights like blue refract more while the light with the longest wavelength red refracts the least. This creates a spectrum

Question 23

List, in the correct order, the colour spectrum produced by the dispersion of white light

Answer 23

Red, orange, yellow, green, blue, indigo and violet.

Question 24

What is monochromatic light?

Answer 24

• Light that has a single frequency
• A laser light is an example of a monochromatic light

Question 25

What are the conditions for total internal reflection?

Answer 25

* The light is travelling from an optically denser medium (higher refractive index) to an less optically dense medium * The critical angle is exceeded

Question 26

What do Optical Fibre do?

Answer 26

Optical fibres transmit light by total internal reflection.

Question 27

What are the key features of an optic fibre?

Answer 27

* Core * Cladding * Protective Coating

Question 28

What are optical fibres used for?

Answer 28

* Internet providers use optical fibres to set up quick and reliable internet connections. * They can be used for endoscopy

Question 29

Do optical fibre lose lots of information?

Answer 29

No they don't they are able to transmit huge amounts of information with few information losses

Question 30

What is the focal length?

Answer 30

The focal length is the distance from the centre of the lens to the principal focus

Question 31

What is the principal focus?

Answer 31

* Light rays that are parallel to the optical axis pass through the lens and converge (come together) at the principal focus. * There is one principal focus on each side of the lens as light can pass through the lens in either direction.

Question 32

What is the image produced by a conveging lens like when the object is more than two focal lengths from the centre of the lens? and Draw it

Answer 32

* The image is real * The image is inverted * The image is diminished (smaller than the object) * Image is between F and 2F * Examples: the eye and cameras

Question 33

What is the image produced by a conveging lens like when the object is between one and two focal lengths from the centre of the lens?

Answer 33

* The image is real * The image is inverted (upside down) * The image is magnified (larger than the object) * Examples are the projector and the photocopier

Question 34

What is the image produced by a conveging lens like when the object is two focal lengths from the lens

Answer 34

* The image is the same size as the object

Question 35

What is the image produced by a conveging lens like when the object is between the principal focus and the centre of the lens?

Answer 35

* The image is erect (the right way up) * The image is Virtual * The image is magnified * The image is also on same side of the lens as the object * Am example is a magnifying glass

Question 36

What is the dispersion of light?

Answer 36

* Dispersion is the seperation of white light into a spectrum (range) of colours * A rainbow is an example of a spectrum that is formed when sunlight is dispersed by raindrops.

Question 37

What is the refractive index of air

Answer 37

1