Waves

A transfer of energy from point A to point B through vibrations without the net movement of particles

The distance from the undisturbed position to the peak or trough of a wave

distance from peak to peak of a wave

centre of compression to centre of compression or rarefaction to rarefaction

The number of waves passing a point per unit time

The time taken for a single wave to pass a point

The distance travelled by a wave each second

Waves where the vibrations occur at 90 degrees to the direction of energy transfer

Solid, liquid, (vacuum for some)

Waves where the vibrations are parallel to the direction of energy transfer

Solid, liquid, gas

compressions and rarefactions

frequency x wavelength

Reflection
Refraction
Transmission
Absorption

A wave hits a boundary between 2 media and does not pass through, but instead stays in the original medium

Flat surfaces

A wave changes speed at the boundary between 2 materials of different densities

A wave passes through a substance

Energy is transferred from the wave into the particles of the substance

Ripple tank (to create waves in water)
Light source (to illuminate waves to create shadows)
Strobe light (to make waves appear stationary so that wavelength can be measured)
Metre rule (to measure distance)
Large sheet (white background as screen for wavefront shadows)
Stopwatch (to time the movement of the waves)

Independant var - frequency
Dependant var - wavelength
Control - depth of water, temp of water

1. Set up apparatus as shown
2. Turn on the power supply and light source to produce a wave pattern on the screen
3. The wavelength of the waves can be determined by using a ruler to measure the length of the screen and dividing this distance by the number of wavefronts
4. The frequency is determined by timing how long it takes for a given number of waves to pass a chosen point and dividing the number of wavefronts by the time taken (s)
5. Record the frequency and wavelength and repeat the measurements
6. Calculate the wave speed

longitudinal

The variations in pressure cause the surface of the solid to vibrate in sync with the sound wave

The frequency which an object tends to vibrate at

Larger

20-20,000 Hz

1. Sound wave travels through auditory canal
2. Pressure variations created by sound wave exert a varying force on the eardrum causing it to vibrate
3. The vibration pattern of the sound wave creates the same pattern of vibration in the eardrum
4. The eardrum vibration is transferred to the three small bones
5. The vibration of these small bones transfers the vibrations to the cochlea
6. In the inner ear, nerve cells detect the sound and send a message through the acoustic nerve to the brain

Sound waves with a frequency above 20 000 hertz

Sound waves with a frequency below 20 hertz

decreases

increases

Sonar
Foetal scanning
Exploration of the earth's core

1. Sonar uses ultrasound to detect underwater objects
2. The sound wave is reflected off the ocean bottom
3. The time it takes for the wave to return is used to calculate the depth of the water (using the known speed of sound in water)
4. The distance the wave travels is twice the water's depth

1. An ultrasound detector is made up of a transducer that produces and detects a bean of ultrasound waves into the body
2. The ultrasound waves are reflected back to the transducer by different boundaries between tissues in the path of the beam eg. Boundary between soft tissue and bone
3. When these echoes hit the transducer, they generate electrical signals that are sent to the ultrasound scanner
4 Using the speed of sound and time of echo return, the detector calculates the distance from the transducer to the tissue boundary
5. By taking a series of measurements across an area, and image can be constructed

P waves and S waves

longitudinal

solids and liquids

Faster

Infrasound

An area on Earth's surface where no direct seismic waves from a particular earthquake can be detected.

transverse

Solids

On the opposite side of earth to an earthquake, only P waves are detected, not S waves. This shadow zone suggests that the mantle is solid, as both waves can pass through it, but the outer core of earth is liquid, so no S waves can penetrate it.

Solids

Wavelength increases
Frequency same
Velocity increases

Oscillate back and forth
Direction of oscillation parallel to direction of energy transfer

Measure many wavefronts and divide by number of wavefronts

Particles at end vibrate around fixed positions
Cause neighbouring particles to vibrate

transverse