2.4 - The nature of waves

Question 1

What is a progressive wave?

Answer 1

A pattern of disturbances traveling through a medium, energy is transferred without a transfer of matter

Question 2

What is a transverse wave? Give examples

Answer 2

The oscillations of the particles are at right angles to the direction of travel of the wave
E-m waves and s-seismic waves

Refer to NC 1

Question 3

What is a longitudinal wave? Give examples

Answer 3

Particles oscillate parallel to the direction of travel
Sound waves and p-seismic waves

Refer To NC1

Question 4

What are the 4 characteristics of a wave?

Answer 4

Wavelength, λ
Frequency, f
Amplitude
Period, t

Question 5

Describe the 4 characteristics of a wave?

Answer 5

Wavelength - the minimum distance between two points oscillating in phase
Frequency - The number of cycles per second
Amplitude - Max displacement, distance from middle of wave to crest ( greater the A, greater the energy being carried), ( 1/2 crest to trough displacement)
Period - Time taken for one complete cycle

Refer NC 2

Question 6

For 2 waves to be in phase or in anti-phase they must have the same ______

Answer 6

frequency

Question 7

What is phase difference

Answer 7

The difference in positions of 2 points within a cycle of oscillation. It is given as a fraction of the cycle or as an angle

Question 8

One whole cycle is given as _____ or _____

Answer 8

2 pi or 360 degrees

Question 9

Points which are oscillating in phase will be multiples of _____ or _____ radians e.g. _ and _

Refer to NC 3

Answer 9

360
2 pi
A and E

Question 10

Points which are oscillating in anti phase are ____ or ____ radians e.g. _ and _

Answer 10

180
1 pi
A and C / B and D

Question 11

If a wave moves a distance, x, in a time, t

speed = distance/ time

Consider specific case when the distance moved by the wave is exactly equal to 1 wavelength, the the time elapsed must be equal to the period T.

Speed = wavelength / Time period
Know that T = 1/f
So wave speed = frequency x wavelength
c = f x λ

What is c?

Answer 11

3 x 10^8 m/s

Question 12

Calculate the frequency of red light when it has wavelength 6.5 x 10^-7m

Answer 12

f = c/λ (3 x 10^8) / (6.5 x 10^-7) = (4.61 x 10^14) Hz

Question 13

What is a polarised wave?

Answer 13

A transverse wave where all the oscillations are in one direction

Refer to NC 4

Question 14

If you try to view plane-polarised light through a 2nd sheet of polaroid that is placed so that its polarising direction is right angles to the polarising direction of the 1st sheet, it will be found that no light is transmitted. In this arrangement the polaroid’s are said to crossed. The 2nd polaroid sheet is acting as an analyser. If the 2 polaroid’s have their polarising direction parallel, then plane polarised light from the 1st sheet can travel through the second. So rotating the analyser through 180˚, we move ____ 0˚to _____90˚ to _____180˚

Answer 14

light
dark
light

See NC 6

Question 15

What are wave fronts?

Answer 15

Lines of constant phase , all points on the wave fronts are in phase.
The wave fronts travel radially from a source and therefore the direction of travel of the waves are along a radial direction (perpendicular to the wave fronts)

See NC 7