Lesson ObjectivesState how light bends when it travels from a medium of

lower index of refraction (less dense, faster) to a medium of higher index of refraction (denser, slower).

State how light bends when it travels from a medium of higher index of refraction (denser, slower) to a medium of lower index of refraction (less dense, faster)

State the condition under which light travels from one medium to another without bending.

Explain the behavior of light using the analogy of a rolling barrel.

RevisionWhat is refraction? What is index of refraction ?

Lower index of refraction faster speed (less dense medium)

Higher index of refraction slower speed (denser medium)

Less dense (faster) to denser (slower) medium For example, air to glass

Angle of incidence and angle of refraction are measured from the normal! Light bends towards the normal.

Angle of refraction is smaller than angle of incidence.

Normal

Angle of incidence

Angle of refraction

Refracted ray

Incident ray

Explanation Use the rolling

barrel as an analogy. One end touches the

grass first and slows down while the other end rolls with the original speed.

As a result, the barrel turns towards the normal.

Concrete

GrassThis end slows down first when it touches the grass. As a result, the barrel turns.

PredictHow will light bend if it travels from air to water? (Index of refraction of air : almost 1 Index of refraction of water : 1.333 Index of refraction of glass is around 1.5. )

Will the angle of refraction smaller or larger than that in the previous case (air to glass)?

Why?

Verification by simulation

http://www.ps.missouri.edu/rickspage/refract/refraction.html

Denser (slower) to less dense (faster) mediumFor example, glass to air Light bends away

from the normal.

The angle of refraction is larger than the angle of incidence

air

glassGlass

(slower medium)

air

(faster medium)

glass

ExplanationUse the rolling barrel

as an analogy. One end touches the

concrete ground first and speeds up while the other end rolls with the original speed.

As a result, the barrel turns away from the normal.

Concrete

Grass

This end speeds up first when it touches the concrete. As a result, the barrel turns.

PredictHow will light bend if it travels from water to air? (Index of refraction of air : almost 1 Index of refraction of water : 1.333 Index of refraction of glass is around 1.5. )

Will the angle of refraction smaller or larger than that in the previous case (glass to air)?

Why?

Verification by simulation

http://www.ps.missouri.edu/rickspage/refract/refraction.html

In conclusion Faster medium to slower medium bends towards normal

Slower medium to faster medium bends away from normal

The greater the difference in the index of refraction between the two medium , the more light bends.

Question: Is it possible that light travels from one medium to another without changing the direction?

Yes, if light strikes the boundary perpendicularly!

Light strikes the boundary perpendicularly

Can you use the analogy of rolling barrel to explain this?Medium 1

Medium 2

Boundary

Exactly how much does light bend?Snell’s law (optional)

How does light bend when it travels from a less dense (faster) to a denser (slower) medium?

How does light bend when it travels from a denser (slower) to a less denser(faster) medium?

Under what condition will light travel from one medium to another without bending?

Can you explain the behavior of light using the analogy of a rolling barrel now?