Physics - Light

Question 1

Are light waves transverse or longitudinal?

Answer 1

Transverse

Question 2

State the three pieces of evidence that suggest light is a wave

Answer 2

It can be reflected, refracted and diffracted

Question 3

State the law of reflection

Answer 3

The angle of incidence equals the angle of reflection

Question 4

What is the angle of incidence?

Answer 4

The angle at which the light travels to the plane

Question 5

What is the normal?

Answer 5

A perpendicular line to the plane, used to measure angles of incidence, reflection and refraction

Question 6

Describe an experiment to investigate the refraction of light and explain the results. Do this using rectangular blocks

Answer 6

• Draw around the rectangular glass block and direct a ray of light through it at 40o.
• Use two crosses to mark the entering ray and the exiting ray.
• Join the crosses to the rectangle and draw the line through the block joining the lines
• Draw the normal at 90 degrees to the surface and measure the incident angle (line entering the block to normal) and refracted angle (line going through the glass block and normal) using a protractor
• Calculate the refractive index using n=sini/sin⁡r
• Repeat for several other angles and take an average of n.

Question 7

Which equation works out the refractive index?

Answer 7

n=sin⁡i/sin⁡r

Refractive index = sin (angle of incidence) divided by sin (angle of refraction)

Question 8

Which equation relates two refractive indices and the angle of incidence/refraction?

Answer 8

𝑛_1 x sin𝜃_1 =𝑛_2 x sin𝜃_2

Refractive index of medium 1 x sin (angle of incidence) = refractive index of medium 2 x sin (angle of refraction)

Question 9

Which equation uses the speed of light to work out the refractive index of a medium?

Answer 9

Refractive index = speed of light (2.998x10^8) divided by the speed of light in the medium

Question 10

Why does refraction happen?

Answer 10

As the wave enters the new medium at an angle (unless it is perpendicular, when there is no refraction) part of the wave enters the new medium earlier and then speeds up or slows down.
This causes the light to change direction.

Question 11

What happens if the light goes from a less dense to more dense medium?

Answer 11

The angle of refraction is smaller than the angle of incidence.

It moves towards the normal

Question 12

What happens if the light goes from a more dense to a less dense medium?

Answer 12

The angle of refraction is larger than the angle of incidence.

It moves away from the medium

Question 13

What happens to the speed of light when it enters a more dense medium (normally)?

Answer 13

It slows down

Question 14

What happens to the speed of light when it enters a less dense medium (normally)?

Answer 14

It speeds up

Question 15

Describe an experiment to investigate the refraction of light using semi-circular blocks and explain the results.

Answer 15

-Aim ray at the curved edge so it emerges leaves at the centre of the flat surface. This way it enters along the normal and doesn’t refract.
Draw around the semi-circular block and mark the mid-point of the flat surface.
Increase the angle at the flat surface until the refracted ray exits along the surface. This is the critical angle. Use two crosses to mark the position of the ray. Remove the semi-circular block and draw a line through the crosses to the mid-point of the flat surface. Draw a normal at 90o to the flat surface and measure the angle between the normal and the line of the ray. This is the critical angle.

Question 16

Describe an experiment to investigate the refraction of light using triangular prisms and explain the results.

Answer 16

Shine white light through the prism. The white light is dispersed into the different wavelengths of light, because the different wavelengths of light are refracted by different amounts

Question 17

What colours are seen when white light is dispersed (in order of most refracted to least refracted)?

Answer 17

Red, Orange, Yellow, Green, Blue, Indigo, Violet (Richard Of York Gave Battle In Vain)

Question 18

How do you investigate the refractive index of glass?

Answer 18

• Draw around the rectangular glass block and direct a ray of light through it at 40o.
• Use two crosses to mark the entering ray and the exiting ray.
• Join the crosses to the rectangle and draw the line through the block joining the lines
• Draw the normal at 90o to the surface and measure the incident angle (line entering the block to normal) and refracted angle (line going through the glass block and normal) using a protractor
• Calculate the refractive index using n=sin⁡i/sin⁡r
• Repeat for several other angles and take an average of n

Question 19

Describe what is needed for total internal reflection

Answer 19

Light goes from high refractive index to low refractive index
Angle of incidence is greater than the critical angle (angle at which light travels at the boundary of the media)

Question 20

Why does dispersion occur?

Answer 20

Each of the different wavelengths that make up white light have different refractive indices

Question 21

What are the sections of the electromagnetic spectrum?

Answer 21

Radio waves, micro waves, infrared waves, visible light, ultraviolet waves, x rays, gamma rays

Question 22

Do the different waves from the electromagnetic spectrum travel at different speeds?

Answer 22

No - they all travel at the same speed through a medium