Refraction Chapter 4

Question 1

What is refraction

Answer 1

the bending of a ray of light when it goes from one medium to another

Question 2

What would be exception- when if there no refraction between two medium

Answer 2

when ray strikes the second medium at right angles

Question 3

What is the angle of incidence

Answer 3

angle between incident ray and the normal

Question 4

What is the angle of refraction

Answer 4

angle between the refracted ray and the normal

Question 5

Does light refract towards or away from the normal

Answer 5

If travelling from a rarer to a denser medium refracts towards the normal.
If travelling from a denser medium to a rarer medium it travels away from the normal.

Question 6

State the laws of refraction

Answer 6

the incident ray, the normal at the point of incidence and the refracted ray all lie in the same plane
the ratio of the sine of the angle of incidence to the sine of the angle of refraction is a constant.
ie. sin i/sin r = n, where n is a constant

Question 7

What is law 2 also known as

Answer 7

snell’s law

Question 8

What is the refractive index

Answer 8

the ratio of sin i to the sin r when light travels from a vacuum or from air into that medium. symbol- n

Question 9

What is the refractive index for any two media

Answer 9

xNy= 1/yNx

Question 10

Where is apparent depth greatest

Answer 10

When viewed vertically above object, apparent depth decreases as you move to the side

Question 11

How and when can you calculate the refractive index of a medium from real and apparent depth

Answer 11

When line of view of an object is perpendicular to the surface of the medium then:
N= Real depth / apparent depth

Question 12

When is light fastest and at what speed

Answer 12

in a vacuum (or air difference is minuscule) at 3 x 10^8m/s

Question 13

How is refractive index of a medium calculated using speed of light

Answer 13

xNy = Cx/ Cy

Ex: for air
airNx = speed of light in air/ speed of light in other medium

Question 14

What is the relationship (effect) of refractive index on the speed of light in that medium

Answer 14

Greater the refractive index the slower the speed of light

Question 15

Explain total internal reflection

Answer 15

when light going from a denser to a rarer medium strikes the second with an angle of incidence greater than the critical angle it does not enter the second medium. It is reflected back into the denser medium

Question 16

What is the critical angle

Answer 16

When light travels from a denser to a rarer medium the angle of incidence whose corresponding angle of refraction is 90 degrees is called the critical angle (c) of those two media

Question 17

What happens to light that strikes point of incidence at critical angle

Answer 17

it skims across the surface

Question 18

Applying Snell’s law how can you find the refractive index of a medium from the critical angle. And use example of air

Answer 18

xNy = sinC

xNa = sinC and so aNx = 1/sin C

Question 19

What is Snell’s window

Answer 19

If you are underwater looking up, light from outside can only enter water through circle of radius r - until critical angle - referred to as snell’s window

Question 20

Where will ray that is shone onto one mirror which is located at right angles to two other mirrors travel back?

Answer 20

back in the direction the original ray came from

Question 21

What are applications of snells window and total internal reflection

Answer 21

safety reflector of bike, reflective road signs

Question 22

What is an optical fibre

Answer 22

A thin transparent rod (usually made of glass) which light can travel through by total internal reflection. They are solid and not hollow

Question 23

Describe how light can escape an optical fibre

Answer 23

If light is bent at too large an angle, ray may strike at angle less than critical angle - therefore no internal reflection and light leaves fibre
If fibre comes into contact with another fibre total internal reflection will not occur as light will travel between fibres of same refractive index

Question 24

How do you prevent light leaving an optical fibre because of same refractive index

Answer 24

coat optical fibre with a layer of glass of lower refractive index

Question 25

Uses of optical fibres

Answer 25

telecommunications
dentists drill
Medical endoscope

Question 26

In the experiment to verify snell’s law how is graph plotted

Answer 26

Sin of all values for i down one axis and sin of all values of r down other axis. Draw straight line through the origin

Question 27

In the experiment to verify snell’s law how the refractive index found from the graph

Answer 27

fins the slope. must use formula y2-y1/x2-x1

Question 28

Why is it more accurate to find the refractive index by graphing In the experiment to verify snell’s law

Answer 28

outliers can be identifies and there is reference to the origin