Sam Ellis Waves

Question 1

2 defining features of transverse waves

Answer 1

Direction of energy propogation is at 90º to the oscillations
Can travel through a vacuum

Question 2

2 Defining features of longitudinal waves

Answer 2

Direction of energy propogation is parallel to the oscillations
need a medium to transfer energy

Question 3

What is meant by amplitude?

Answer 3

Magnitude of maximum displacement.

Question 4

What makes a wave a wave?

Answer 4

a disturbance in a medium that carries energy without a net movement of particles

Question 5

How would you calculate phase difference?

Answer 5

2π(d/lambda) the whole cycle times the fraction of the whole wave

Question 6

When are waves in phase?

Answer 6

0, 2π, 4π, 6π, 8π etc

Question 7

When are waves completely out of phase?

Answer 7

odd multiples of π

Question 8

What is the principle of superposition?

Answer 8

when two or more waves with the same frequency
travelling in opposite directions overlap,
the resultant displacement is the sum of displacements of each wave

Question 9

What is polarisation?

Answer 9

Reducing transverse wave oscillations in a particular direction.

Question 10

What is a real life application of polarisation?

Answer 10

Polaroid lenses in sunglasses for driving - the road will reflect waves in a plane, the glasses will have filters oriented such that the reflections do not show

Question 11

On a stationary wave - what is an anti node?

Answer 11

A point with MAX amplitude

Question 12

On a stationary wave - what is a node?

Answer 12

A point with no displacement.

Question 13

What is total destructive interference, when does it occur?

Answer 13

When two waves completely out of phase interfere they completely cancel each other out leading to no resultant displacement.

Question 14

When will a standing wave occur?

Answer 14

superposition of two waves of the same frequency and amplitude travelling in opposite directions.
Constructive inteference occours at anti nodes
total destructive at nodes

Question 15

What must be true about stationary waves formed in a loudspeaker?

Answer 15

there must be a minima (node) at one end and a maxima (antinode) at the end with the loudspeaker.

Question 16

With reference to motion, what is true about nodes and anti nodes

Answer 16

The nodes and antinodes do not move along the string. Nodes are fixed and antinodes only move in the vertical direction

Question 17

What is Diffraction?

Answer 17

the spreading out of waves when they pass an obstruction.

Question 18

What is meant by coherent?

Answer 18

The same frequency
A constant phase difference

Question 19

What is path difference? What must be true about it for constructive / destructive interference to occur?

Answer 19

The difference in distance travelled by two waves from their sources to the point where they meet
The condition for constructive interference is a path difference of nλ
The condition for destructive interference is a path difference of (n + ½)λ

Question 20

Give 3 precautions when using a laser.

Answer 20

Never look directly at a laser or its reflection

Don’t shine the laser towards a person

Don’t allow a laser beam to reflect from shiny surfaces into someone else’s eye

Question 21

What do D w and s stand for in the fringe spacing seperation

Answer 21

w = fringe spacing

D = Distance from screen to slits

s = slit seperation

Question 22

When is diffraction the most prominent?

Answer 22

Diffraction is the most prominent when the width of the slit is approximately equal to the wavelength

Question 23

What is the only property of a wave that changes when it diffracts?

Answer 23

The only property of a wave that changes when it diffracts is its amplitude

Question 24

What would happen if the blue laser were to be replaced with a red laser

Answer 24

The wavelength of red light is longer so the light would diffract more
The intensity fringes would therefore be wider

Question 25

Narrower slit = ?

Answer 25

MORE DIFFRACTION
Less intense
more spread out

Question 26

What is different about energy in stationary waves vs progressive waves

Answer 26

Stationary waves store energy, unlike progressive waves which transfer energy.

Question 27

What does T and ‘Mu’ stand for in the first harmonic equation?

Answer 27

Mu is MASS per unit length
T is tension

Question 28

Sketch a single slit diffraction pattern for blue laser light.

Answer 28

Bright central maxima
Other maxima half the width

Question 29

With single slit diffraction how does the amount of diffraction change with the slit spacing?

Answer 29

More wide = less diffraction

Question 30

If we have a longer wavelength say red compared to blue what happens to diffraction pattern through the same slit?

Answer 30

The wavelength of red light is longer so the light would diffract more
The intensity fringes would therefore be wider

Question 31

If the wavelength is longer it diffracts…

Answer 31

MORE

Question 32

What do all the symbols stand for in dSin(ø) = nY?

Answer 32

d = slit spacing
n = order
lambda = wavelength
ø = angular separation between orders

Question 33

Conditions for TIR?

Answer 33

The angle of incidence > the critical angle
The refractive index n1 is greater than the refractive index n2

Question 34

If the angle of incidence was 55º and TIR occured what is the other angle?

Answer 34

55º also