12.4 Flashcards
Standing / stationary wave definition
- Wave remains in constant position with no net transfer of energy
- Characterised by nodes and antinodes
How are stationary (standing) waves formed
• 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
What is a node
Point in stationary wave where amplitude is always zero
What is an antinode
Point in stationary wave where amplitude is always maximum
Why are the amplitudes and intensities of nodes always zero (stationary waves)
- Two progressive waves are in antiphase
- Displacements cancel out
- Displacement is always zero
Why are the amplitudes and intensities of antinodes always maximum (stationary waves)
- Two progressive waves are in phase
- Displacements are summed
- Displacement is always maximum
What is the relationship for the distance between adjacent antinodes / nodes in stationary waves
- λ / 2 m
* In phase
Describe the phase difference along a stationary wave
• 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
How are stationary waves formed using microwaves
• 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
