SP4 WAVES

SP4a Describing Waves

• Wavelength: distance from a point on one wave to the same point on the next.Usually measured in metres
• Amplitude: the height of a wave, measured from the middle of the wave to the top or bottom.The greater the amplitude of a sound wave the louder the sound
• Wavefronts: a useful way of picturing waves from above.Each wavefront is used to represent a single wave
• Frequency: number of waves passing a point every second (it is helpful to think of it as being the waves per second) meausred in hertz (Hz). For sound, the wave frequency determines the pitch and for light the frquency determines the colour
• Period: the length of time it takes for a single wave to pass a point
• Velocity: speed of the wave in the direction its travelling. Waves travl at different speed in different materials
• Sea waves transfer energy to the shore. When waves hit the land, the energy is transferred to the land and can wear it away
• Waves on the surface of water are transverse waves. Particles in the water move up and down as a wave passes- the particles are not carried to the shore
• Transverse waves: the particles are travelling at right angles to the direction the wave is moving
• Longitudinal waves: the particles move back and forth in the same direction as the wave is travelling
• Earthquakes and explosions produce seismic waves that travel through the Earth
• Electromagnetic waves: are transverse waves and do not need a medium to travel. E.g. light, radio, microwaves

SP4b Wave Speeds

• distance(m)= speed (m/s) x time (s)
• Velocity (m/s)= frequency (Hz) x wavelength (m)
• measuring waves on water:

1. set up the ripple tank with about 5cm depth of water

2. adjust the height of the wooden rod so that it just touches the surface of the water

3. switch on the lamp and motor and adjust until low frequency waves can be clearly observed

4. measure the length of a number of waves then divide by the number of waves to record wavelength.

5. count the number of waves passing a point in ten second then divide by ten to record the frequency

6. calculate the speed of the waves using: wave speed = frequency x wavelength

Hazards include: electrical components near water can cause damage to components so secure electrical components before adding water taking care not to splash

Measuring Waves in Solids                                   

1) suspend a metal rod horizontally using clamp stands and rubber bands

2) hit one end of the rod with a hammer. Hold a smart phone with a frequency app near the rod and note down the peak frequency

3) measure the length of the rod and write it down. The wavelength will be twice the length of the rod

4) Use the frequency and wavelenght to calculate the speed of sound in the rod

SP4c Refraction

• Most waves travel…