Refraction

Question 1

Refraction

Answer 1

The change in speed of a wave when it passes from one medium to another
Normally causes a change in direction

Question 2

Optical Density

Answer 2

Measures using a refractive index (symbol n; no units) n >= 1 (n = 1 in air)

Question 3

Refractive Index

Answer 3

The ratio of the speed of light in a vacuum (c) to the speed of light in a medium (v)
n = c/v
The speed of light through a medium will always be less than that through a vacuum

Question 4

Snell’s Law

Answer 4

Refraction Law
nSin(θ) = Constant
θ: Angle between the ray and the normal (Line perpendicular to the boundary)

Question 5

Refraction into different mediums

Answer 5

When moving into a more optically dense medium (higher n)
Light refracts towards the normal
Light slows down
Vice Versa
Larger differences in refractive indices means a larger refraction effect is observed
If refractive indices are equal, no refraction takes place
If θ = 90, the ray continues straight

Question 6

Experiment to Determine the Refractive Index of a Glass Block

Answer 6

Draw around the block
Shine the ray box through the long side of the glass block
Mark the incident and emerging rays
Number the corresponding rays
Change the angle of incidence 5+ times, record and number rays
Draw normals and record angles of incidence and refraction using a protractor
Plot a graph (gradient is the refractive index)
Y-axis is sin(θ incident), X-axis is sin(θ refractive)

Question 7

Total Internal Reflection

Answer 7

C: Critical Angle
θ < C: Refraction and partial reflection
θ = C: Light travels along the boundary between the media and 90 to the normal
θ > C: Total Internal Reflection

Question 8

Conditions for Total Internal Reflection

Answer 8

Light is travelling from a higher to lower refractive index
Angle of incidence > Critical Angle

Question 9

Critical Angle

Answer 9

sinC = n1/n2
When the angle of incidence is C the angle of refraction is 90

Question 10

Total Internal Reflection Definition

Answer 10

When the angle of incidence is greater than the critical angle then all the light reflects at the boundary

Question 11

Experiment to find the Critical Angle`

Answer 11

A narrow beam from a ray box hits the curved edge of a semi-circular glass block at 90 (No refraction)
Measure the angle of refraction (Incident angle when leaving the glass block)
Increase this angle until the ray travels along the boundary
Measure this angle