# Waves Extended

### Phase and Phase difference

For waves to be in phase they must have the same wavelength and frequency. Phase merely refers to the waves being 'in step' with one another.

Wave Equations

It is possible to calculate the period of a wave from its frequency using the following equation:

Further calculations allow the waves speed to be calculated from its frequency and wavelength.

### Measuring wavelength and calculating frequency

It is possible to measure the wavelength and calculate the frequency of a sound wave using a microphone and an oscilloscope (c.r.o).

#### Ripple tank

The ripple tank allows waves to be represented using water waves.

Refraction displayed by water moving from a deep area to a shallow area:

The wave speed and wavelength decrease, however the frequency remains
constant. Vibrator coherence is achieved by using the same vibrating strip
to ensure the frequency of vibrations is constant.

Diffraction

Diffraction is the spreading out of waves as they travel through a narrow
gap or around an object. It can only be observed in a lab for light waves
because the wavelengths are so small that a very narrow gap is required.

Points of Note

Note that the wave medium controls the wave speed. Therefore if frequency is doubled then the wave speed doesn't change but the wavelength is half as small because:

Note that you may also be required in the exam to Prove v = f? using the
following series of calculations:

### Polarisation

A Polaroid only allows waves to vibrate in one direction. Transverse waves vibrate in all directions perpendicular to the direction of travel and therefore if two Polaroid’s are used, when one is rotated through 180 degrees no light is transmitted. Polarisation can only occur for transverse waves, therefore sound cannot be polarised.

Test for polarisation by placing a polarising grid and rotating the detector.