Refractive Index

Explain why light refracts

It enters a medium of a different optical density, causing the wave to change speed, so it changes direction

Explain whether light refracts towards or away from the normal when entering a more optically dense material

Light slows down, so bends towards the normal

Explain whether light refracts towards or away from the normal when entering a less optically dense material

Light speeds up so bends away from the normal

What happens to the wavelength when light enters a new medium

Changes

What happens to frequency when light enters a new medium

Stays constant

When light enters a more optically dense material, what happens to wavelength

Decreases

When light enters a less optically dense material, what happens to wavelength

Increases

Why is light slower in materials

It interacts with particles

Refractive index

The ratio between the speed of light in a vacuum and the speed light in a material

What is n in the refractive index equation

The refractive index of the material

What is v in the refractive index material

The speed of light in that material

Refractive index equation

n = c/v

Angle of incidence

The angle between the normal and incoming light

Angle of refraction

The angle between the refracted ray and the normal

What is θ₁ in Snell’s law

Angle of incidence

What is θ₂ in Snell’s law

Angle of refraction

Snell’s Law equation

n₁sinθ₁ = n₂sinθ₂

Experiment to find the refractive index of a glass block

1- Place a glass block on a piece of paper and draw around it.

2- Use a ray box to shine a beam of light onto the glass block

3- Trace the path of the incoming and outgoing beams of light

4- Remove the block and join up the two paths with a straight line

5- Measure the angles of incidence and refraction, substitute 1 in for the refractive index of air and find the refractive index of the block with Snell’s law

How to improve the refractive index experiment

-Turn off the lights

-Use large angles for smaller percentage uncertainty

-Narrower beam of light

When does the critical angle of a material occur

When the refracted angle is at a right angle to the normal

Explain why the critical angle is when the angle of refraction is at a right angle

When light enters a less optically dense medium, it speeds up, so bends away from the normal. The greater the angle of incidence, the greater the angle of refraction. Eventually, the angle of refraction will be inside the block. The lowest angle possible for this is the critical angle as the refracted ray has just entered the block by being 90 degrees to the normal

When does total internal reflection occur

-The angle of incidence is greater than C

-Light is entering a less optically dense medium

Critical angle equation

sinC = 1/n

When does the critical angle equation apply

If the boundary is material-air where the material is more optically dense than air

How to investigate total internal reflection

1- Shine a light ray into the curved face of a semi-circular block

2- Vary the angle of incidence until the light beam refracts so much that it exits the block along the straight edge (θ₁ = C)

3- If you increase the angle of incidence beyond this, the ray is totally internally reflected

Why should the light be shone through the curved face of a semi-circular block when investigating TIR and not the flat face

The light will enter at right angles for every angle of incidence, whereas for a flat face it would only enter at one