p5.2- optics- defraction, refraction, TIR, lenses, image formation, polarisation

Question 1

What is refraction?

Answer 1

When the waves are approaching the interphase between two medias at an angle the change in speed causes a change indirection as well.

Question 2

Why does refraction happen?

Answer 2

When the waves pass from one medium to another, there is a change in speed.
The frequency remains constant, so there is a change in wavelengths.

Question 3

What is the refractive index?

Answer 3

A measure of the amount pf refraction caused by different materials.
It is equal to the ratio of light in a vacuum to the speed of light in a material.
n=c/v

c= speed of light in air
v=speed of light in medium

Question 4

What does Snell’s law show?

Answer 4

The relationship between direction and refractive index

Question 5

What is Snell’s law?

Answer 5

n1 sin θ1 = n2 sin θ2

n1= refractive index of material light is travelling from
n2=refractive index of which light is travelling into
θ1=measured angle of incidence
θ2= measured angle of refraction

Question 6

What is airs refractive index?

Answer 6

1- the other material will always be compared to air.

Question 7

What is dispersion?

Answer 7

It is the spreading of white light into its full spectrum of wavelengths

Question 8

What are the equations for dispersion if the ray enters the prism from air?

Answer 8

sin θ1=c ×sin θ2/fλ

sin θ2=fλ×sin θ2/c

Question 9

Why does the smallest wavelengths bend the most towards the normal?

Answer 9

As frequency stays constant throughout refraction, and the speed of light in a vacuum must be constant, if we keep the same angle of incident then the sine of the angle of refraction will be proportionate to the wavelength.
-violet( smallest wavelength)= bend most
-red( largest wavelength)=bend least

Question 10

Why does wite light disperse when it passes throughs prism ?

Answer 10

-Because the light will change speed and travel more slowly in a dense medium.
-As light bends it splits and bends towards the normal.
- The single beam separates into different colours because they have different wavelength and therefore bends at different angles towards the medium
- Dispersion

Question 11

What are the conditions for total internal refraction?

Answer 11

• Light must be travelling from a more dense medium to a less dense medium.
  -The angle of incidence must be grater than the critical angle

Question 12

What is the equation for working out The refractive index of the more dense material from its critical angle?

Answer 12

n=1/sin θ

Question 13

What is the method for working out a materials refractive index from its critical angle?

Answer 13

• Use a semi- circle block of your material and use a lamp with a slit, to shine a singular ray through the box.
  -Adjust the lamp until the refracted ray is directly on top of the barrier
  -Measure the angle of incidence ray and work out the refractive index of material using
  -n=1/sin θ
• Repeat with different angle to try and find the most accurate critical angle.

Question 14

What does a concave/diverging lens look like?

Answer 14

It caves inward and spread the light rays out.

Question 15

What does a convex/ converging lens look like?

Answer 15

It curves outwards and directs the rays inwards towards a point.

Question 16

What is the equation for power of a lens?

Answer 16

Power=1/focal length

Question 17

How do you add lens powers?

Answer 17

You add convex power and minus concave power.

Question 18

What is diffraction?

Answer 18

The spreading of wave energy through a gap or around an object and the waver energy spreads into the space behind the gap.

Question 19

what does the amount of diffraction depend on?

Answer 19

The wavelength

Question 20

How does the size of the gap effect the diffraction?

Answer 20

-If the wavelength as the same size as the gap you get maximum diffraction.
-if the gap is too small then no energy can pass through and that is why there may not be diffraction.
- of the gap is too large there will be little effect as the wave will pass through undisturbed.

Question 21

what happens at constructive interference when light passes through a diffraction grating?

Answer 21

• Bright maxima’s are formed.

Question 22

what happens at destructive interference when light passes through a diffraction grating?

Answer 22

Dark minima spots are formed.

Question 23

How does the dark bands correlate and the distance between the slits?

Answer 23

Space between dark bands=1/distance between two slits.

Question 24

What is the diffraction grating equation?

Answer 24

nλ=dsinθ

Question 25

What is the equation for intensity?

Answer 25

Intensity Power/Area

Question 26

What is the critical angle ?

Answer 26

The angle of incidence which the angle reflects at 90 degrees.

Question 27

What is the equation used to calculate the critical angle?

Answer 27

SinC= 1/n

Question 28

What does electron diffraction provide evidence for ?

Answer 28

The wavelike nature of electrons. It suggests that particles can demonstrate wavelike properties.

Question 29

If electrons didn’t have a wavelike nature, describe the effect you would see when they’re passed through a slit.

Answer 29

A single bright region would be formed

Question 30

What is total internal reflection?

Answer 30

Its where all the light is reflected back at the boundary between two mediums.
It occurs when light is travelling from a more dense medium to a less dense medium and the incident angle is greater than the critical angle.

Question 31

What is the focal length of a lens?

Answer 31

The distance between the centre of the lens and the focal point

Question 32

What is the real image ?

Answer 32

One that can be projected onto a screen and is always inverted.
They a\re consequences of light meeting at there focal point.

Question 33

What is a virtual image?

Answer 33

Formed on the same side of the lens of the objected and cannot be projected onto a screen.

Question 34

How do you work out the magnification of an object?

Answer 34

image height/ object height

Question 35

What is plane polarisation?

Answer 35

When the oscillation of light in restricted to one plane.