5. Stationary Waves

Question 1

What is a stationary wave?

Answer 1

The superposition of two progressive waves with the same frequency (or wavelength) and amplitude, moving in opposite directions

Question 2

Is energy transmitted by stationary waves or progressive waves?

Answer 2

Progressive waves

Question 3

How can you set up a stationary wave?

Answer 3

Using an oscillator to generate a wave in a string and a boundary for the wave to be reflected at a fixed point

Question 4

What is a resonant frequency?

Answer 4

The frequencies where the overall pattern does not move along - it just vibrates up and down so the string forms oscillating loops

Question 5

Are stationary waves transverse of longitudinal?

Answer 5

Transverse

Question 6

What are nodes?

Answer 6

Points on the wave where the amplitude of the vibration is 0

Question 7

What are antinodes?

Answer 7

Points on the wave with maximum amplitude

Question 8

What frequencies can an exact number of half wavelengths fit on the string?

Answer 8

Resonant

Question 9

What interference occurs at a node?

Answer 9

Total destructive interference

Question 10

What interference occurs at an antinode?

Answer 10

Constructive interference

Question 11

When is a stationary wave only formed?

Answer 11

At a resonant frequency

Question 12

What is the first harmonic?

Answer 12

A special type of resonant frequency that can only fit one wavelength on the string. It is also when the stationary wave is vibrating at its lowest possible resonant frequency

Question 13

What is the second harmonic?

Answer 13

It has twice the frequency of the first harmonic and contains 2 half wavelengths on the string

Question 14

What is the third harmonic?

Answer 14

It has three times the frequency of the first harmonic and contains 1 and a half wavelengths on the string

Question 15

What is the wavelength of a stationary wave showing the first harmonic?

Answer 15

Double the length of the string

Question 16

What is the wavelength of a stationary wave showing the second harmonic?

Answer 16

The length of the string

Question 17

What other ways, other than the string method, can you set up stationary waves?

Answer 17

1. Using microwaves

2. Stationary sound waves - powder in a tube of air

Question 18

Describe the method of the microwaves setting up a stationary wave

Answer 18

1. Reflect microwave beam at a metal plate
2. The superposition of the wave and its reflection produces a stationary wave
3. Find nodes and antinodes by moving the probe (connected to meter or loudspeaker) between the microwave transmitter and the reflecting plate
4. Meter and loudspeaker receive no signal at nodes and maximum signal at antinodes

Question 19

Describe the method of the stationary sound waves

Answer 19

1. Loudspeaker produces stationary sound waves in the glass tube with powder in it
2. The powder laid along bottom of tube is shaken away from the antinodes but left undisturbed at the nodes
3. Distance d between each pile of powder (node) is half a wavelength
4. Find the frequency from the signal generator to calculate the speed of the sound wave