Waves - Chapter 11

Question 1

Progressive waves?

Answer 1

An oscillation that travels through matter or a vacuum in some cases

it transfers energy from one place to another without moving particles along the wave

the particles vibrate from an equilibrium position

Question 2

What is a restoring force?

Answer 2

particles start at an equilibrium position and are displaced before oscillating back to their original position.

Restoring force from neighbouring particles pulls particles back to their starting position.

Question 3

How to represent longitudinal AND transverse waves with a wave profile?

Answer 3

use a displace time graph - each time the graph reaches 0 it is a compression , then rarefaction then compression

when the wave starts going down, it is a compression

Question 4

Phase difference

Answer 4

the difference between displacements of particles along a wave or on different waves.

Particles with distances of integer wavelength are in phase e.g 0, 360, 720 or 0, 2pi, 4pi

if the phase difference is 180 or pi/2, then they are completely opposites in displacements and are on anti phase.

Question 5

displacement symbol and unit and definition

Answer 5

a vector quantity of distance measured from the equilibrium position

symbol s

unit m

Question 6

amplitude symbol and unit and definition

Answer 6

a measure of the maximum displacement of a particle in a wave from its equilibrium position

unit m

symbol A

Question 7

wavelength

Answer 7

the minimum distance between two points in phase on a wave
unit m
symbol lambda

Question 8

Time Period

Answer 8

the time taken for one point on wave to travel one wavelength
unit s
Symbol T

Question 9

Frequency

Answer 9

The number of wavelengths passing a point per unit time
unit Hz
symbol f

Question 10

wave speed

Answer 10

the distance travelled by the wave per unit time
unit m s ^ -1

Question 11

why is f = 1 / t?

Answer 11

Time period is the amount of time for one wavelength to pass

frequency is number of wavelengths that pass per second

so if time period of a wave is 1s , frequency is equal to 1 wave / 1 second = 1

if time period is 0.5s, frequency is equal to 1 wave / 0.5 second = 2

Question 12

what is the timebase

Answer 12

the time base represents the horizontal length of one square on an oscilloscope. it can be set to a distance as the y axis is set to different voltages

Question 13

what happens to waves when they are refracted from more to less dense medium

Answer 13

the wave slows down, bends towards the normal, and wavelength decreases

Question 14

what is diffraction

Answer 14

diffraction is a phenomenon when a wave passes through a gap in an obstacle, the wave spreads out
it is most significant when the wavelength of the gap matches that of the wave

Question 15

What is polarisation?

Answer 15

polarisation is when a wave is restricted to one plane only
it is unique to transverse waves as longitudinal waves are already oscillating in one plane, that is parallel to the direction of energy transfer

Question 16

Partial polarisation

Answer 16

when transverse waves reflect of surfaces, they become partially polarised.
more waves are oscillating in one direction but not all of them
Happens to light waves - most waves end up horizontally

Question 17

What is intensity and its equations

Answer 17

Intensity is defined as the radiant power passing through a surface per unit area
I = P / A

I is inversely proportional to 1/ r^2

I is proportional to amplitude^2

Question 18

EM waves with wavelengths

Answer 18

radio waves: >10^6 - 10^-1
Microwaves : 10^-1 - 10^-3
Infrared: 10^-3 - 7x10^-7
Visible: 7 x 10^-7 - 4 x 10^-7
Ultraviolet: 4 x 10^-7 - 10^-8
X-rays: 10^-8 - 10^-13
Gamma rays: 10^-10 - <10^-16

Question 19

How are EM waves classed?

Answer 19

EM waves are classed based on their origin, not frequencies or wavelengths
hence why gamma and x-rays overlap
e.g. x rays come from fast moving electrons
gamma rays come from unstable nuclei

Question 20

Properties of EM waves

Answer 20

em waves are transverse, they can be plane polarised
they can be diffracted, reflected, refracted.
they don’t require a medium
they travel at the speed of light in a vacuum

Question 21

how to use a ripple tank to observe wave effects

Answer 21

an oscillated paddle is connected to an electric motor in a tank
this will create transverse waves on the surface of the water
the depth can be adjusted to modelcrefraction
reflection can be observed against the edges of the tank
diffraction can be model by adding a slit into the tank

Question 22

how can polarisation of light be demonstrated

Answer 22

using polaroid filter. Polaroid filters are made of long strips of crystals.
when the polaroid filters are placed on each other with the same orientation, the intensity is maximum.
As one is rotated to 90 degrees the intensity falls to a minimum because light falls to a

Question 23

what are the two conditions for total internal reflection

Answer 23

the light must be travelling from a material with a higher refractive index to a material with a lower refractive index

the angle of incidence must be greater than or equal to the critical angle (Sin C = 1 / n )