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Regular Reflection

Light travels in straight lines through a uniform medium. This is called rectilinear propogation.

Light that falls on flat, smooth surfaces undergoes regular reflection. The converse is called irregular reflection.

The Law of Reflection

The angle of incidence will equal the angle of reflection.

θi = θr

Refraction

Refraction is a change in the direction of a light wave due to a change in its speed as it passes from one medium to another.

Refraction

• Not all of the light will be refracted. Some of the light is also reflected.

• The refracted ray makes an angle with the normal line called the angle of refraction.

• Depending on the index of refraction, the refracted ray will either bend toward the normal line or away from the normal line.

• When light passes from a medium with a higher refractive index into a medium of lower refractive index, it is bent away from the normal. The converse is true.

Index of Refraction

v

cn

The index of refraction is a ratio of the speed of light in a vacuum compared to the measured speed of light in a particular medium.

Snell’s Law

Snell’s Law describes the relationship between the angle of incidence and angle of refraction.

1

2

2

1

sin

sin

n

n

2211 sinsin nn

whereas, the subscript 1 refers to incidence and the subscript 2 refers to refraction.

Snell’s Law

Snell’s Law

Example 1

Example 2

Total Internal Reflection

When the angle of refraction is exactly 90o, the angle of incidence is referred to as the critical angle.

Any angle of incidence greater than the critical angle will result in total internal reflection.

Just as with total internal reflection, a critical angle can only be obtained when light is moving from a medium with a higher index of refraction to a medium with a lower index of refraction.

Critical Angle

Example 3

Applications