Module 4 Refraction

Question 1

Definition of refraction

Answer 1

change in speed of a wave as it passes from one medium to another causing a change in direction

Question 2

What is the refractive index?

Answer 2

the ratio of speed of light in a vacuum over speed of light in a medium

Question 3

Which direction are lightwaves refracted by when passing through medium when going from less to more dense?

Answer 3

towards the normal (when going from less to more dense)

Question 4

What happens when light crosses the boundary of two different mediums along the normal?

Answer 4

no change in direction but the light changes speed

Question 5

What is the relationship between n and the angle of refraction?

Answer 5

greater the index the smaller the angle

Question 6

What effects are there when two refractive indices are equal?

Answer 6

ray of light continues along it’s original pathway

Question 7

What stays the same during refraction?

Answer 7

frequency

Question 8

What happens if the angle of incidence is the critical angle?

Answer 8

refracted light travels along the boundary of the two media (angle of reflection = 90º)

Question 9

How are wavelength and amount of refraction related?

Answer 9

as wavelength decreases amount of refraction which takes places increases (ie bigger change in direction)

Question 10

What is Snell’s law?

Answer 10

nsin(θ)=constant

Question 11

Describe how the refractive index, and thus the critical angle of glass (to air) can be calculated using a RECTANGULAR glass block

Answer 11

• Place the block of glass on a sheet of paper and draw a trace around the block
• Draw a normal at a given point on the side of a block
  -Point a laser at this point, and using a protractor, measure the angle of incidence
  -Draw a dot where the beam of light exits the glass block and join the dot between entrance and exit
  -Measure the angle to the normal inside the block - this is angle of refraction
• use nsin(θ)=constant (with n=1 for glass) to find refractive index for glass
• then use sin(C) = 1/n to find critical angle C

Question 12

How can the critical angle be found using a semicircular glass block

Answer 12

-Place block on a piece of paper and trace

-Shine a laser/light ray at the curved side so that it is at right angles to edge

-vary the angle of incidence by adjusting the light ray until the beam refracts along the straight edge

-Mark the direction, and thus the angle of incidence of the light ray