Waves

Question 1

Define frequency and give its units

Answer 1

Number of waves passing through a point per Second measured in Hz

Question 2

Define wavelength

Answer 2

Distance Between two adjacent peaks or troughs on a wave

Question 3

Define Amplitude

Answer 3

The maximum displacement of a wave from its equilibrium position

Question 4

What is time period

Answer 4

Number of seconds for the wave to cycle 1 wavelength
1/ frequency

Question 5

What is Phase Difference

Answer 5

What fraction of a cycle are two points stationed away from each other

measured in radians

Question 6

What is a longitudinal wave?

Answer 6

A wave in which direction of the particles is parallel to the energy transfer

There are rare fractions (areas of low pressure) and compression (areas of high pressure)

Question 7

What is a Transverse Wave

Answer 7

Waves where the direction of the particles is perpendicular to energy transfer

Em waves

Question 8

In a EM wave how are the electric and magnetic fields arranged

Answer 8

Perpendicularly

Question 9

What does a polarising filter do?

Answer 9

Only allows oscillations in a specific plane by restricting the vibrations to a specific direction

Question 10

How is polarisation used as an evidence of the nature of transverse waves?

Answer 10

Polarisation can only occur if a waves oscillations are perpendicular to the direction of travel

As longitudinal waves would be able to pass through any polarisation filter.

Question 11

How is polarisation used in antennas?

Answer 11

Tv and radio signals are usually plane polarised by the orientation of the rods on the broadcasting aerial.
So the Receiving aerial must be alined in the same way to receive the signal at full strength

Question 12

What is a stationary wave?

Answer 12

A wave which transfers no energy and whose position of maximum and minimum amplitude (antinodes) & nodes are constant

Caused by the interference between 2 identical progressive waves traveling in opposite directions

Each particle doesn’t experience the entire amplitude of the wave

Question 13

What is a node?

Answer 13

A point on a stationary wave where the displacement is 0

Question 14

What is an anti node?

Answer 14

A point on a stationary wave of maximum magnitude of displacement

Question 15

What are the conditions for a stationary wave to exist?

Answer 15

Waves must be of same
- frequency
- wave length
- amplitude
Must be travelling in opposite directions

Often met when a wave is reflected back on its self

Question 16

How are stationary waves produced?

Answer 16

• Formed from the superposition of 2 progressive waves traveling in opposite directions with he same frequency, wavelength and amplitude

-Waves form antinodes of maximum displacement when two are met in phase, due to constructive interference

-Waves form fixed position nodes when the two meet completely out of phase, due to destructive interference

Question 17

Describe the first harmonic for a stationary wave with two closed ends

Answer 17

2 Nodes at either end with an anti node in the middle

Question 18

Describe the second harmonic for a stationary wave with 1 closed end and 1 open end

Answer 18

2 anti nodes and 3 nodes
1 Node in the middle
2 nodes at each end
Anti nodes stationed half way between eahc node

Question 19

What is the formula for anti nodes and nodes

Answer 19

where n = number of harmonic
Number of Antinodes = n

Number of nodes = (n+1)

Question 20

What is a Progressive wave?

Answer 20

• A wave that transfers Energy outside of a system
  -Waves which are not confined to a system
• Each particle experiences the entire amplitude of the wave

Question 21

What is an Oscilloscope?

Answer 21

A device which plots the signal of a voltage supply and shows how it varies over time.

Question 22

How do an Oscilloscope work? ( 5 steps)

Answer 22

1) Electron gun is aimed at a fluorescent screen

2) 2 Y-Plates are positioned either side of the beam

3) 2 X plates are positioned either side of the beam perpendicular to y plates

4) when the potential difference of the chosen supply is applied across either of the plates electrons path are displaced towards the positive of the plates

5) the higher the potential difference the higher the electrons are displaced, and greater distance away from the centre of the fluorescent screen. This is then plotted on the graph.

Question 23

RMs Voltage =

Answer 23

Voltage peak * 2^(-1/2)

Question 24

What is the formula you need the calculate the wavelength of nth harmonic of a stationary wave?

Answer 24

Question 25

What is the formula you need the calculate the frequency of nth harmonic of a stationary wave?

Answer 25

Question 26

What is the formula that is used to workout the tension in a string within a stationary wave?

Answer 26

(in formula book)

Question 27

What is the phase difference of two particles in the stationary wave that:

Have the same direction towards the Equilibrium Position?

Have opposite directions towards the Equilibrium Position?

Answer 27

1) In-Phase 0 or 2Pi

2) Counter Phase Pi

Question 28

How do you predict the way a particles going to move in a stationary wave?

Answer 28

Look at the particle left of your chosen one.
Your particle will mimic this

Question 29

What is Path Difference

Answer 29

Number of wavelengths in terms of displacement between two points

Question 30

Answer 30

Signal strength goes through a series of max and minimum points

at certain distances the direct and reflected waves interfere constructively to produce a maximum signal and interfere destructive to create a minimum signal

This is due to the phase difference between the reflected and direct waves changing periodically as distance to x decreases.

Question 31

How do you prove that diffraction will occur for a specific slit gap

Answer 31

1) calculate de Broglie wavelength
2) use diffraction equation Sin(x) = landa/slit spacing to calculate first order
3) if this gives a viable answer if wavelength is smaller then gap
4) Then yes diffraction would be observable if the wavelength and split spacing are in the same magnitude

Question 32

How do you calculate Mass per unit length

Answer 32

Density of metal * cross sectional area in m^3 x 1m

Question 33

Explain why the first harmonic calculation for a wire at high tensions produces frequencies higher then expected

Answer 33

Wire could neck/ thin at parts if the tension is very large causing a lower mass per unit length, making the frequency produced higher then expected.