Waves- Progressive waves, standing waves and polarisation

What is a wave?

A disturbance that can transfer energy without transferring matter as a whole

Longitudinal wave

A type of wave, where the oscillations occur parallel to the direction of energy transfer.

Compression

Areas of high pressure due to particles being close together

Rarefactions

Areas of low pressure due to particles being spread apart

Transverse waves

A type of wave, where oscillations occur perpendicular to the direction of energy transfer.

Examples of longitudinal waves

Sound waves

Examples of transverse waves

Electromagnetic waves and water waves

Displacement

Distance of a point on the wave from its equilibrium position

Amplitude

The maximum displacement from the equilibrium position

Wavelength

The distance between two consecutive points that are in phase

Period

Time taken for one complete oscillation

Frequency

Number of complete oscillations per second

In phase

When two points have a phase difference of 0 or 2pi

Antiphase

When two points have a phase difference of pi

Path difference

The difference in distance travelled by two waves to reach a specific point.

When does polarisation occur?

Polarisation occurs when oscillations are confined to a single plane.

What are the applications of polarisation?

• Polaroid sunglasses reduce glare by blocking horizontally polarised light.

• Antennas must be aligned to the plane of the wave

Why can’t longitudinal waves be polarised?

Their oscillations are along the direction of travel, so there's no perpendicular direction to filter.

What is the principle of superposition?

When two or more waves meet at a point, the total displacement is the vector sum of the individual displacements.

Constructive interference

Waves in phase; amplitudes add.

Destructive interference

Waves in anti-phase; amplitudes subtract.

The conditions for sustained interference

• Waves must be coherent

• Similar amplitude and same type

What does coherent mean?

Same frequency and constant phase difference

How is a stationary wave formed?

When two waves of identical frequency, amplitude, and speed move in opposite directions and interfere with each other

What are nodes?

Points of zero displacement in a stationary wave.

What are antinodes?

Points of maximum amplitude in a standing wave.

What are the features of a stationary wave?

There is no net energy transfer

Fundamental harmonic

The fundamental harmonic is the simplest standing wave with only one antinode and two nodes

When does resonance occur?

Resonance occurs when the frequency of a vibration matches the natural frequency of an object, causing the object to vibrate

Where is resonance used?

In musical instruments and in measuring the speed of sound