Section 3 - Waves

Question 1

What is the definition of frequency and what are the units?

Answer 1

The number of waves passing through a point per second (hertz) Hz

Question 2

What is the definition of wavelength?

Answer 2

The distance between 2 adjacent peaks on a wave

Question 3

What is the definition of amplitude?

Answer 3

The maximum displacement of the wave from its equilibrium position

Question 4

How can you find out 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 fractions of a cycle

Question 6

What is a longitudinal wave?

Answer 6

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

Question 7

What is a transverse wave? Give an example

Answer 7

• Waves where the particle oscillations are perpendicular to the direction of energy transfer
  Electromagnetic waves

Question 8

How fast do electromagentic waves travel in a vacuum?

Answer 8

Speed of light

Question 9

What is the relationship between the magnetic field and electric field?

Answer 9

Perpendicular

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 the nature of transverse waves?

Answer 11

Polarisation can only occur if a wave’s oscillations are perpendicular to its direction of travel (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 rods on the transmitting aerial
• 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 amplitude 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

• The waves must be of the same frequency, wavelength and amplitude
• They must be travelling in opposite directions
  These conditions are often met when a wave is reflected back onto itself

Question 17

How are stationary waves produced?

Answer 17

A stationary wave is formed from the superposition of 2 progressive waves, travelling in opposite directions in the same plane, with the same frequency, wavelength and amplitude
* Where the waves meet in phase, constructive and destructive interference occurs so antinodes (regions of maximum amplitude) form
* Where the waves meet completely out of phase, destructive interfernece occurs and nodes (regions of no displacement) form