2.2 Refraction

Question 1

Refraction

Answer 1

Change in direction of light as it moves between 2 different mediums causing a change in speed

Question 2

Snell’s Law

Answer 2

For light travelling from one medium to another the ratio of sin i/sin r is a constant

Question 3

What happens to wave as it passes from one medium to another where it travels at slower speed?

Answer 3

Wave bends towards normal
Speed of wave decreases
Frequency remains constant
Wavelength decreases

Question 4

Refractive index

Answer 4

Ratio of the sin of angles in medium one to the sin of the angle in material two

Question 5

Refractive index formula

Answer 5

Speed of light in a vacuum/air / speed of light in material

Question 6

Refractive index in air/vacuum

Answer 6

1

Question 7

Relative refractive index

Answer 7

Light moving from one medium to another where neither is air/vacuum

Question 8

Relative refractive index formula

Answer 8

1n2 = c1/c2 = n2/n1 = sin01/sin02

Question 9

How is snell’s law verified from graph?

Answer 9

Gradient of graph is a constant
Sin i directly proportional to sin r - straight line through the origin

Question 10

What happens if the direction of light is reversed?

Answer 10

Material 2 to material 1
Refractive index 2n1 is related to 1n2 like this:
2n1 = 1/1n2

Question 11

Total internal reflection

Answer 11

Ray of light passing from glass into air bending away from normal

Question 12

Critical angle

Answer 12

Particular value of angle of incidence where the angle of refraction is 90

Question 13

Conditions for total internal reflection

Answer 13

Angle of incidence = greater than critical angle
Light must be travelling from a more dense material towards the less dense material (higher rf to a lower rf)

Question 14

Equation for the critical angle

Answer 14

N = 1/sin0c

Question 15

Role of optical fibres in endoscope

Answer 15

Flexible, narrow bundle of optical fibres
Light is directed into body through endoscope, image is transmitted back to operator
Total internal reflection allows light to reflect
Fibres needed placed side by side in a bundle to obtain an image

Question 16

Use of endoscope

Answer 16

Diagnosis - doctor examine diseased area
Taking a biopsy - small sample to be tested
Performing a small operation on diseased area
Removing an obstruction

Question 17

Advantage of using endoscope

Answer 17

Non-invasive as all procedures can be carried out without having to open up patient

Question 18

Where are optical fibres used?

Answer 18

Endoscopes - medical instruments
In communications

Question 19

Step index optical fibres

Answer 19

Fine glass core surrounded by cladding of glass with lower refractive index than core

Question 20

What will happen to light shone into fine glass core at an angle greater than critical angle?

Answer 20

Totally internally reflect at boundary between core and cladding

Question 21

Why should the core be narrow in step index optical fibres?

Answer 21

Cuts down on multi-node dispersion and stops light broadening out

Question 22

Transmission of image in step index optical fibres

Answer 22

Relative position of fibres @ each end is same, bundle give coherent image
To transmit, fibres in bundle have to be kept in same relative positions, each fibre is contributing to formation of image
Called a coherent bundle

Question 23

Disadvantage of coherent bundle

Answer 23

Expensive to manufacture

Question 24

Transmission of light in step index optical fibres

Answer 24

Fibres don’t have to be coherent and are wider
Cheaper to manufactured
Incoherent bundles used for introducing light

Question 25

Why are incoherent bundles used for introducing light in the transmission of light?

Answer 25

Light going in many directions