Waves

Question 1

Which type of wavelength diffracts more, Short or long?

Answer 1

The LONGER the wavelength the more the wave diffracts .

Question 2

What is constructive interference?

Answer 2

When a crest meets a crest or a trough meets a trough and interferes with each other a maximum amplitude is produced. This is called constructive interference.

Question 3

What is destructive interference?

Answer 3

Destructive Interference is when a crest meets a trough and interferes with each other, minimum or zero amplitude is produced. This is called destructive interference.

Question 4

How is an Interference pattern created?

Answer 4

regions of constructive and destructive interference produce the interference pattern.

Question 5

How is a maximum produced?

Answer 5

When 2 wave crests or 2 wave troughs arrive at the same point at the same time, they are said to be in phase. (Constructive Interference).

Question 6

What is the path difference formulas ?

Answer 6

Path difference = mλ OR

Path difference = (m+1/2)λ

Question 7

Why are there two different path difference formulas?

Answer 7

At different order maximum’s and minimums the number required at m is different.
( The path difference to the mth maximum) = mλ
m=0 at the central maximum
m=1/2 at the 1st order minimum
m=1 at the first order maximum
m=1 1/2 at the 2nd order minimum ……

Question 8

What is the Interference equation?

Answer 8

mλ= dsinθ   where : 
m= the order maximum/minimum 
d = The separation of the slits
θ = The angle from the centre to maxima or minima

Question 9

How do you find the separation of the slits?

Answer 9

Say a grating has 1000 lines per mm
You would take the numerical value for the unit or measurement being used, in this case mm ( 1x10^-3) and you would divide it by the number of lines per that unit measurement, in this case 1000.

Question 10

Explain the interference of white light?

Answer 10

• The central maximum is white
  + All wavelengths interfere constructively at this point
• All other maxima are spectrums . ( ROYGBIV)
• Violet is the closest to the central maximum in EVERY spectrum.
  + Since mλ=dsinθ violet has a smaller wavelength than red so the angle , θ, is smaller for violet than red in EVERY spectrum.

Question 11

Describe a continuous Spectrum

Answer 11

Continuous spectrum’s have all colours of the rainbow with no gaps

Question 12

What spectra is produced when elements are heated?

Answer 12

Line emission spectrum

Question 13

Describe a line emission spectrum.

Answer 13

Individual coloured lines like a barcode on a black background

Question 14

Describe a line absorption spectrum.

Answer 14

Opposite of a line emission spectrum, black lines like a barcode with a coloured background.

Question 15

Describe the Bohr model of the atom

Answer 15

• Electrons orbit the nucleus in “discrete” energy levels
  The Ionisation Level is furthest from the nucleus and has zero potential energy.
  The ground state is closest to the nucleus.
  -

Question 16

What happens when electrons lose or gain energy in the bohr model of the atom?

Answer 16

• When energy is given to a gas ( via heat/electricity/light) electrons are excited and move up energy levels
• When electrons lose energy, the fall down energy levels and release photons. ( 1 photon per electron)

Question 17

What is the equation used to find out energy loss among “discrete” energy levels?

Answer 17

E2-E1 = hf   where : 
E2 = Higher energy level 
E1 = Lower energy level 
h = Plancks constant 
f = Frequency

Question 18

What is snell’s law?

Answer 18

n = Sinθ1 / Sinθ2   OR 
Sinθ1/Sinθ2 = λ1/λ2 = V1/V2  where ; 
θ1 = angle in air ( incidence) 
θ2 = angle in denser material ( refraction)
V = Speed 
λ - Wavelength
YOU CAN mix and match the equation

Question 19

What is always on the top of the equation in Snell’s law ?

Answer 19

Top of the equation always has the less dense medium regardless of which way the light in travelling.

Question 20

What will happen when the refractive index gets bigger?

Answer 20

The bigger the refractive index, the larger the change in speed and wavelength.
Frequency will stay the same, no matter what the refractive index is.

Question 21

What is the critical angle?

Answer 21

The critical angle in glass, is when the refracted ray in air is equal to 90 degrees. ( therefore can’t get any bigger)

Question 22

What happens when the angle in glass is bigger than the critical angle?

Answer 22

When the angle in glass is bigger than the critical angle, the light is not refracted but is totally internally reflected.

Question 23

What is the formula for Critical angle?

Answer 23

Sinc=1/n where :
n=refractive index
c=critical angle in glass

Question 24

What colour is refracted the most?

Answer 24

Short wavelength ( violet) are refracted most.

Question 25

what is refraction the opposite of ?

Answer 25

Diffraction

Question 26

What happens to the refractive index depending on the colour of the light?

Answer 26

The refractive index of a substance is higher for short wavelength violet light than it is for long wavelength red light.

Question 27

What is the difference in the Refraction/Diffraction of different wavelengths? (colours)

Answer 27

Diffraction grating diffracts red light the most

Refraction- violet light refracted the most

Question 28

Why can Laser light cause eye damage?

Answer 28

Because a laser beam is parallel and has a high irradiance it can cause serious damage to the human eye