LT: refraction and dispersion

Question 1

what is refractive index?

Answer 1

refractive index of a material, n, is the ratio of the speed of light in a vacuum to the speed of light in the medium.

n = c/v

where c is the speed of light in a vacuum (3.00 x 10⁸) and v is the speed of light in the medium.

since refractive index is a ratio, it has NO UNITS.

Question 2

refractive index of and speed of light in vacuum

Answer 2

refractive index: 1.0000
speed of light: (3.00 x 10⁸)

Question 3

refractive index of and speed of light in air

Answer 3

refractive index: 1.0003
speed of light: (3.00 x 10⁸)

Question 4

refractive index of and speed of light in water

Answer 4

refractive index: 1.33
speed of light: (2.26 x 10⁸)

Question 5

refractive index of and speed of light in glass

Answer 5

refractive index: 1.50
speed of light: (2.00 x 10⁸)

Question 6

refractive index of and speed of light in diamond

Answer 6

refractive index: 2.40
speed of light: (1.25 x 10⁸)

Question 7

refractive index of and speed of light in human cornea

Answer 7

refractive index: 1.39-1.41
speed of light: (2.14 x 10⁸)

Question 8

how to calculate speed of light in a medium?

Answer 8

n = c/v

sub. known refractive index into n
and (3.00 x 10⁸)/speed of light in vacuum into c

Question 9

what is refraction of light?

Answer 9

the bending of light as it passes from one medium to another of different optical density.

Question 10

conditions for refraction

Answer 10

1. the light ray passes from one medium to another of different optical density
2. the angle of incidence is more than 0°
   (draw normal to check)

Question 11

what happens when light travels into a medium of higher optical density (higher refractive index)?

Answer 11

light bends towards the normal
i > r

Question 12

what happens when light travels into a medium of lower optical density (lower refractive index)?

Answer 12

light bends away from the normal
i < r

Question 13

why does a drinking straw appear bent in water?

Answer 13

as light exits from water, which has a higher refractive index,

into air, which has a lower refractive index,

light undergoes refraction.

thus, the light rays seen by the eye trace back to an image that appears to be shallower than the object.

Question 14

why does light disperse?

Answer 14

white light is made of a spectrum of seven colours: red, orange, yellow, green , blue, indigo, violet.

when white light passes into a different medium, each colour of light slows down to a different extent.

thus, the light rays for each colour refract by different angles, resulting in the spreading out of light.