12.4

Question 1

Standing / stationary wave definition

Answer 1

• Wave remains in constant position with no net transfer of energy
• Characterised by nodes and antinodes

Question 2

How are stationary (standing) waves formed

Answer 2

• Two progressive waves of same frequency
-ideally same amplitude

• Propogate in opposite directions
• Superpose
• Only certain frequencies travelling along a given system will produce stationary waves

Question 3

What is a node

Answer 3

Point in stationary wave where amplitude is always zero

Question 4

What is an antinode

Answer 4

Point in stationary wave where amplitude is always maximum

Question 5

Why are the amplitudes and intensities of nodes always zero (stationary waves)

Answer 5

• Two progressive waves are in antiphase
• Displacements cancel out
• Displacement is always zero

Question 6

Why are the amplitudes and intensities of antinodes always maximum (stationary waves)

Answer 6

• Two progressive waves are in phase
• Displacements are summed
• Displacement is always maximum

Question 7

What is the relationship for the distance between adjacent antinodes / nodes in stationary waves

Answer 7

• λ / 2 m

* In phase

Question 8

Describe the phase difference along a stationary wave

Answer 8

• Between adjacent nodes all particles/points are in phase

• phase difference is zero
• all reach maximum positive displacement at same time
• amplitudes differ
• max amplitude at antinode

• On different sides of node particles/points are in antiphase

• phase difference is π
• particles on one side of node reach maximum positive displacement at same time as particles on other side reach maximum negative displacement

Question 9

How are stationary waves formed using microwaves

Answer 9

• Use microwave transmitter

• Reflect microwaves off metal sheet
-two microwaves of same frequency are travelling in opposite directions

• Microwave receiver detect changes in intensity between nodes and antinodes
• Distance between transmitter and metal sheet is adjusted until receiver detects series of nodes and antinodes
• Distance between successive nodes/antinodes = λ/2