3.1 progressive and stationary waves

Question 1

Define frequency and give its units

Answer 1

The number of waves passing through a point per second

(hertz) Hz

Question 2

Define wavelength

Answer 2

The distance between 2 adjacent peaks on a wave

Question 3

Define amplitude

Answer 3

The maximum displacement of a wave from its equilibrium position

Question 4

How can you find the time period of a wave using its frequency?

Answer 4

T=1/f

Question 5

What is phase difference and what is it measured in?

Answer 5

How much a particle/wave lags behind another particle/wave. Measured in radians , degrees or in fractions of a cycle

Question 6

What is a longitudinal wave?

Answer 6

A wave of which oscillation of the particles is in the direction of energy transfer.
There are rarefractions (areas of low pressure)
There are compressions (areas of high pressure)

Question 7

What is a transverse wave with examples?

Answer 7

Waves where the particle oscillations are perpendicular to the direction of energy transfer.
ie: electromagnetic waves

Question 8

How fast do electromagnetic waves travel in a vacuum?

Answer 8

3x10^8 m/s speed of light

Question 9

What ways do the magnetic and electric waves travel to each other?

Answer 9

They travel at right angles to each other

Question 10

What does a polarising filter do?

Answer 10

Only allows oscillations in one plane

Question 11

How is polarisation used as evidence of how transverse waves behave?

Answer 11

Polarisation can only happen if a waves oscillations are perpendicular to the direction of travel (as they are in transverse waves)

Question 12

How is polarisation used in antennas ?

Answer 12

TV and radio signals are usually plane-polarised by the orientation of the transmitting aerial , so the receiving aerial must be aligned in the same plane of polarisation to receive the signal at full strength

Question 13

What is a stationary wave ?

Answer 13

A wave which transfers no energy and whose positions of maximum and minimum amplitudes are constant

Question 14

What is a node?

Answer 14

A point on a stationary wave where the displacement is 0

Question 15

What is an antinode ?

Answer 15

A point on a stationary wave with maximum displacement

Question 16

What are the conditions for a stationary wave to be produced ?

Answer 16

1) waves must be of the same frequency , wavelength and amplitude
2)They must travel in opposite directions
These conditions are often met when a wave is reflected back on itself

Question 17

How are stationary waves produced?

Answer 17

A stationary wave is formed from the supersition of 2 progressive waves travelling in opposite directions along the same plane with the same frequency wavelength and amplitude

1) Where the waves meet in phase constructive interference occurs so antinodes are formed
2) Where the nodes meet completely out of phase destructive interference occurs and nodes are formed

Question 18

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

Answer 18

It consists of 2 nodes on either end and an antinode in the middle

Question 19

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

Answer 19

Consists of 2 nodes and 2 antinodes with one node being at the close end and one antinode being at the open end