# IB DP Physics: SL复习笔记4.5.2 Nodes & Antinodes

### Nodes & Antinodes

• A standing wave is made up nodes and antinodes
• Nodes are locations of zero amplitude and they are separated by half a wavelength (λ/2)
• Antinodes are locations of maximum amplitude
• The nodes and antinodes do not move along the wave
• Nodes are fixed and antinodes only oscillate in the vertical direction

Nodes and antinodes of a stationary wave of wavelength λ on a string of length L at a point in time

#### The Formation of Nodes and Antinodes

• Nodes are formed as a result of destructive interference
• The amplitude of both waves cancel out
• Antinodes are formed as a result of constructive interference
• The amplitude of both waves add together

Nodes and antinodes are a result of destructive and constructive interference respectively

• At the nodes:
• The waves are in anti-phase meaning destructive interference occurs
• This causes the two waves to cancel each other out
• At the antinodes:
• The waves are in phase meaning constructive interference occurs
• This causes the waves to add together

#### Phase on a Standing Wave

• Two points on a standing wave are either In Phase
• Points that have an odd number of nodes between them are in anti-phase
• Points that have an even number of nodes between them are in phase
• All points within a "loop" are in phase

Points A, B and D are all in phase. While points A and D are in antiphase with point C

#### Worked Example

Which row in the table correctly describes the length of L and the name of X and Y?