Total internal reflection

Question 1

What does total internal reflection involve?

Answer 1

reflection and refraction

Question 2

total internal reflection

Answer 2

• involves a semi circular shaped transparent substance/a curved material
• when light is shined through the curved side, some of it is reflected and some is refracted
• can only occur when light travelling from a dense material meets a boundary with a less dense material

(doesn’t occur when light enters glass, only when it leaves the material)

-can also take place with sound

Question 3

role of reflection

Answer 3

as the angle of incidence increases (incident ray moves down the curved side) the angle of refraction will increase

when it reaches 90 degrees, the ray of light travels along the outer surface of the glass

the angle of incidence is the critical angle

Question 4

the critical angle

Answer 4

the angle of incidence at which the ray of light travels along the outer edge of the glass

Question 5

What happens above the critical angle?

Answer 5

the light is totally internally reflected

Question 6

What does increasing the angle of incidence do?

Answer 6

increases the angle of refraction

the light ray is refracted closer to the edge of the glass/closer to parallel

Question 7

What densities does total internal reflection depend on?

Answer 7

light must be travelling into a less dense material

Question 8

reflection below the critical angle

Answer 8

light is always reflected at the same angle as the angle of incidence

Question 9

endoscopes

Answer 9

can be used to look inside patients’ bodies

make use of optical fibres

allow keyhole surgery
(surgery conducted through a small cut in the body to speed up recovery time)

Question 10

Describe the structure of an endoscope

Answer 10

an eyepiece lens is at the patients’ end
the other end has an objective lens

optical fibres run through the tube

enclosed by an outer sheath

light from a light source is transferred into the tube using optical fibres

the light is totally internally reflected inside the tube, transferring an image

Question 11

fibre optic cables

Answer 11

make use of total internal reflection to transfer data using light

light pulses are sent along the cable, they are reflected along the inside above the critical angle so that all the light is reflected

Question 12

Draw a labelled diagram to show how total internal reflection (TIR) is used in optical fibres [3]

Answer 12

2 smaller tubes at the top/bottom of a larger one

the smaller ones are cladding
the middle is the core

rays of light travel through by being reflected

rays of light meeting the boundary between the cladding and the core are totally internally refracted

Question 13

Explain the two conditions necessary for total internal reflection to take place in reference to optical fibres [2]

Answer 13

1) the cladding must have a smaller refractive index (lower density) than the core
2) the waves must meet the boundary at an angle greater than the critical angle

Question 14

Describe the conditions for total internal reflection to occur for a ray of light [3]

Answer 14

light needs to travel from a denser material to a less dense material

angle of incidence needs to be above the critical angle

Question 15

Describe how an endoscope works [3]

Answer 15

light is sent into the optical fibre above the critical angle and is totally internally reflected along the fibre to the object being viewed

it is than reflected back up to the observer

Question 16

Explain the role played by reflection and refraction in an endoscope [4]

Answer 16

light rays are reflected at the interface between the fibre and the outer sheath so that the light rays travel down into the patient and are then reflected back

the angle at which the light waves meet this boundary must be greater than the critical angle for total internal reflection to occur

the outer sheath must be less dense than the fibre