P14 Light

Question 1

What is the Law of Reflection?

Answer 1

Angle of Incidence = Angle of Reflection

Question 2

What is the “Normal”?

Answer 2

The line perpendicular to the mirror

Question 3

What is the angle of incidence?

Answer 3

The angle between the incidence ray and the normal.

Question 4

What is the angel of reflection?

Answer 4

The angle between the reflected ray and the normal.

Question 5

What is refraction?

Answer 5

The changing direction of a wave (light) as it travels between mediums of different densities

Question 6

What makes a colour?

Answer 6

Visible light with it’s own narrow band of wavelength and frequency.

Question 7

What is specular reflection?

Answer 7

Reflection from a smooth surface in a single direction.

Question 8

What is diffuse reflection?

Answer 8

Relfection from a rough surface causing scattering

Question 9

How do colour filters work?

Answer 9

By absorbing certain wavelengths of visible light (colours) and transmitting other wavelengths of visible light (colour).

Question 10

What is the colour of an opaque object determined by?

Answer 10

It’s determined by which wavelengths of light (colour) are more strongly reflected.

Question 11

What happens to wavelengths which are not reflected?

Answer 11

They are absorbed

Question 12

What makes an object appear to be white?

Answer 12

If all the wavelengths are reflected equally.

Question 13

What makes an object appear black?

Answer 13

If all the wavelengths are absorbed

Question 14

Objects that transmitt light are either ….

Answer 14

… transparent or translucent

Question 15

What two things change about a wave when it passes between mediums of different densities?

Answer 15

Speed and direction

Question 16

How does a lens form an image?

Answer 16

By refracting light

Question 17

How does a convex lens work?

Answer 17

Parallel rays of light converge (join together) to focus at the principal focus.

Question 18

How does a concave lens work?

Answer 18

Parallel rays diverge (spread out) to focus at the principal focus.

Question 19

What is the focal length?

Answer 19

The distance from the lens and principal focus

Question 20

The image produced by a convex lens is …

Answer 20

…. either virtual or real

Question 21

The image produced by a concave lens is ….

Answer 21

…. always virtual

Question 22

What is a real image?

Answer 22

When light is converged (comes together) to form an image on a screen or retina.

Question 23

What is a virtual image?

Answer 23

When light rays diverge so the object appears to be in a different place.

Question 24

How do you calculate magnification?

Answer 24

Magnification = image height / object height

- magnification is a ratio so it dosen’t have an SI unit

Question 25

Generally, what should image and object height be measured in?

Answer 25

mm or cm if measurement isn’t specified

Question 26

In a ray diagram how is a convex lens represented?

Answer 26

An line with arrow heads (<—->)

Question 27

In a ray diagram, how is a concave lens represented?

Answer 27

A line with “V” heads (>—–<)

Question 28

How do you draw a ray diagram for an image through a convex lens?

Answer 28

• from the top point of the object draw a line parallel going to the lens
• draw a second converging refracted line passing through the principal focus
• draw a third line from the top point of the object right through the middle of the lens

(note : these steps are done because light is being converged)

Question 29

How do you draw a ray diagram for an image through a concave lens?

Answer 29

• from the top point of the object draw a line parallel going to the lens
• draw a second diverging refracted line passing through the principal focus
• draw a third line from the top point of the object right through the middle of the lens

(note : these steps are being done because light is being diverged)

Question 30

How do you find the refractive index?

Answer 30

Sin(i) / Sin(r)

Question 31

What can refractive index tell us?

Answer 31

How much slower light travels through a medium compared to a vacuum or air (which is 1)

Question 32

What is the critical angle?

Answer 32

The angle of incidence when Total Internal Reflection is achieved.

   - *above this all light is reflected, no light is refracted out*

Question 33

What must happen for Total Internal Relfection (TIR) to occur?

Answer 33

1) Angle of incidence must be larger than the critical angle

2) Ray must be in medium with higher refractive index (‘more optically dense’)

Question 34

How do you carry out the Light Required Practical?

Answer 34

1) Make a narrow ray of light by slotting a slit into the ray box

2) Place the glass block on top of a piece of paper and trace it.

3) Draw a normal to the block

4) Align the incident ray with the meeting point between the normal and surface of the block.

5) Draw the refracted ray and reflected ray

6) Using a protractor measure the angle of: incidence, reflection and refraction

7) Repeat the experiment with either different material or different incidence