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3.Waves - A level Physics > 3.5 - Refraction > Flashcards

3.5 - Refraction Flashcards

1
Q

When does refraction occur?

A

When light passes a boundary between 2 different transparent media at an angle.

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2
Q

What happens at the boundary between two mediums when light refracts?

A

The rays of light undergo a change in direction.

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3
Q

How is the angle of direction taken in refraction?

A

From the normal (perpendicular to the surface of the boundaries).

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4
Q

What happens to the direction of light when going from a less dense to more dense medium?

A

The light bends towards the normal.
(air to glass)

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5
Q

What happens to the direction of light when going from a more dense to less dense medium?

A

The light bends away from the normal.
(glass to air)

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6
Q

What happens to the direction of light when passing along the normal?

A

Light does not bend at all.

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7
Q

Why does light refract when going to a more or less dense medium?

A

The change in direction occurs due to the change in speed when travelling in different substances (light slows down when going into a denser medium so it bends towards the normal).

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8
Q

What is the refractive index? (n)

A

A property of a material which measures how much light slows down when passing through it.

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9
Q

How do you calculate the refractive index? (equation)

A

n = c / cₛ
c = the speed of light in a vacuum (3 x 10⁸) (ms⁻¹)
cₛ = the speed of light in a substance (ms⁻¹)

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10
Q

What is a material with a high refractive index called?

A

An optically dense material.

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11
Q

Why must n always be above 1 when calculating the refractive index?

A

Because the speed of light in a substance can never be higher than the speed of light in a vacuum.

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12
Q

What is Snell’s Law?

A

n₁sinθ₁ =n₂sinθ₂
n₁ = the refractive index of material 1
n₂ = the refractive index of material 2
θ₁ =the angle of incidence of the ray in material 1
θ₂ = the angle of refraction of the ray in material 2

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13
Q

Where are the angles θ1 and θ2 are always taken from?

A

The normal.

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14
Q

What is the angle of incidence?

A

The angle between the normal and the ray of light.

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15
Q

What is the critical angle? θ𝒸

A

When the angle of incidence goes over 90 degrees and the ray changes from just refracting to total internal reflection.

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16
Q

How can the critical angle be found?

A

sin θ𝒸 = n₁ / n₂

17
Q

What is total internal reflection (TIR)?

A

When the angle of incidence is greater than the critical angle and the incident refractive index n₁ is greater than the refractive index of the material at the boundary n₂.

18
Q

What are the 2 conditions for TIR?

A
  • The angle of incidence > the critical angle
  • The refractive index n₁ is greater than the refractive index n₂
19
Q

How do you calculate the angle of reflection?

A

critical angle - angle of incidence

20
Q

What are 2 things fibre optics are used for?

A

Communications - (telephone/internet)
Medical imaging - (endoscopes)

21
Q

What do fibre optics do?

A

Utilise the phenomenon of total internal reflection to send high speed light signals over large distances.

22
Q

What is the cladding of a fibre optic?

A

The material with a lower refractive index that surrounds the core.

23
Q

What is the core of a fibre optic?

A

An optically dense material (like plastic/glass).

24
Q

What are the 3 components of optical fibres?

A
  • core
  • cladding
  • outer sheath
25
Q

Why is the core more optically dense?

A

So that total internal refraction occurs.
n cladding < n core

26
Q

What are the 3 purposes of the outer sheath?

A
  • Prevents physical damage to the fibre
  • Strengthens the fibre
  • Protects the fibre from the outside from scratches
27
Q

What are 3 purposes of the cladding?

A
  • Keeps signals secure and maintains quality
  • Keeps the core away from adjacent fibre cores so there is no crossover signals
  • Prevents core from damage
28
Q

What is material dispersion?

A

When white light is used instead of monochromatic light.

29
Q

What is pulse broadening?

A

Wen material dispersion occurs and the difference frequencies of light travel at different rates.
The pulses that emerge are longer than they should be.

30
Q

What is modal dispersion?

A

When the light pulses in the optical fibre spread out due to the different angles of incidence in the original pulse.

31
Q

Why is the core so narrow?

A

To prevent modal dispersion.

3.Waves - A level Physics (5 decks)

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