U3 - Waves

Question 1

What is amplitude?

Answer 1

Maximum displacement of a particle from rest position.

Question 2

What is frequency ! In terms of waves?

Answer 2

The number of waves passing through a point each second. (Measured in Hz or s^-1)

Question 3

What is wavelength?

Answer 3

The shortest distance between two points in phase

Question 4

What is displacement? (in terms of particles and waves)

Answer 4

The distance of a particle from equilibrium in direction of energy propagation.

Question 5

What is time period?

Answer 5

The time taken for one complete wavelength to pass a point.

Question 6

What are mechanical waves
(with examples)?

Answer 6

Waves that rely on a medium to travel through (e.g., sound waves and seismic waves).

Question 7

What are electromagnetic
waves?

Answer 7

Oscillating electric and magnetic fields that are in phase and
perpendicular to one another.

Question 8

Give 3 properties of
electromagnetic waves

Answer 8

● Can travel through a vacuum.
● Travel at the speed of light (through a vacuum).
● Are all transverse.

Question 9

What are the sections of the electromagnetic spectrum and the properties of either side?

Answer 9

Radio - Longest wavelength ⇒ lowest frequency ⇒ least penetrating.
Microwaves, Infrared, Visible, Ultraviolet, X-ray
Gamma - Shortest wavelength ⇒ highest frequency ⇒ most
penetrating.

Question 10

In what range does visible
light lie?

Answer 10

400 nm to 700 nm.

Question 11

Describe the motion of transverse waves?

Answer 11

The direction of vibrations are perpendicular to the direction of energy propagation (transfer)!

Question 12

What types of waves cannot be polarised and why?

Answer 12

Longitudinal waves
As their oscillations occur in one direction, so there’s no need to distinguish between ‘different’ oscillation directions as there’s only one.

Question 13

What is unpolarised light?

Answer 13

A mixture of waves oscillating in different planes.

Question 14

How can you make a wave polarised, what does this do and how does it work?

Answer 14

By passing it through a polarising filter which allows waves oscillating in one plane to pass lowering the new wave’s intensity.
Oscillations in the other directions are absorbed by the molecules in the polarising filter.

Question 15

Give a use of Polarising filters ????

Answer 15

Light is reflected from the road surface is partially plane polarised. Polarising sunglasses can stop the horizontally polarised light getting into your eyes.

Question 16

Describe the motion of longitudinal waves.

Answer 16

The direction of oscillations are parallel to the direction of energy propagation

Question 17

How is polarisation used in transmission and reception?

Answer 17

Radio and TV waves are transverse electromagnetic waves.
As they leave the transmitter, they are polarised.
If the aerial of the receiver on the roof of a house is not aligned in the same plane of polarisation, reception will be reduced in quality.
There will be no reception if the the aerial receiver is aligned at 90 degrees to the original plane of polarisation.

Question 18

How does increasing the amplitude and wavelength affect particles on a longitudinal wave?

Answer 18

Increasing the amplitude makes particles vibrate further from rest position.
Increasing the wavelength increases the distance between consecutive areas of compression/ rarefactions.

Question 19

What does in phase and in anti phase mean?

Answer 19

In phase - peaks line up w peaks and troughs line up w troughs.
In anti phase - peaks line up w troughs and vice Versa !

Question 20

When are two waves coherent and what does this mean?

Answer 20

Two waves are said to be coherent if they have the same frequency, wavelength and a constant phase relationship .

Question 21

Which types of diffraction occur as the gap size varies?

Answer 21

When gap size = wavelength, maximum diffraction.

When gap size &laquo_space;wavelength, wave reflects back.

When gap size > wavelength, diffraction occurs at edges.

Question 22

What is path difference and what can it lead to ?

Answer 22

Path difference is the difference in distances travelled by two coherent waves.
Path difference leads to phase difference.

Question 23

What is phase difference for both stationary and progressive waves ?

Answer 23

For standing waves, the phase difference can only ever be π/2, π, 3π/2, 2π radians.

For progressive waves, the phase difference is the fraction of a cycle between two vibrating particles. Hence 2πd / λ.

Question 24

What happened when two waves meet? What does this mean,

Answer 24

They superpose meaning the resultant displacement is now the vector sum of the individual displacements.

Question 25

When does constructive interference occur?

Answer 25

When two waves some whole wavelength, nλ, apart (otherwise known as in phase) superpose.

Eg. The waves constructively interfere to construct a wave of greater amplitude.

Question 26

When does maximum destructive interference occur?

Answer 26

When two waves some half- wavelength apart (n + 1/2) λ apart, otherwise completely out of phase waves, superpose.

The waves destructively interfere to give a wave of zero amplitude.