Stationary waves

Question 1

Stationary wave

Answer 1

Two progressive waves, each with the same frequency and wavelength, moving in opposite direction.
It creates a wave which doesn’t transfer energy from one place to another.

Question 2

Node

Answer 2

They are points on a stationary wave that have zero amplitude. Meaning they are stationary.

Question 3

Antinode

Answer 3

They are points on a stationary wave with maximum amplitude.

Question 4

Resonant

Answer 4

Stationary waves can only have certain frequencies which are resonants.
When an object is made to oscillate at its natural frequency (fundamental) we get large amplitude oscillations, this is called resonance.

Question 5

Harmonics

Answer 5

The first resonant is called the first harmonic also known as the fundamental. It has two nodes and one antinode. The second harmonic has three nodes and two antinodes.

Question 6

Wavelength

Answer 6

The wavelength of a stationary wave can be found from the distance that covers two complete antinodes. Each loop is half a wavelength. The first harmonic L = lamda/2. The second harmonic (two antinodes) happens when the distance between the two fixed ends is at one wavelength L = lamda (one wavlength)

Question 7

Applications of stationary waves

Answer 7

• The vibrations of guitar strings can be modelled as stationary waves, with nodes at the fixed points of the strings.
• To change the frequency of the harmonics of the sting and the pitch, the string is held down onto a fret. This creates a node at one at one end of the string.
• when plucking the string we get all the harmonics added together. Every instrument has its own tone.

Question 8

Applications of stationary wave 2

Answer 8

When increasing the thickness of the string it increases the mass per unit length.
The frequency of the harmonics on string is inversely proportional to the mass per unit length of the string.
Strings that are thicker have a greater mass per unti length and so they produce a sound with a lower pitch.