P12: Wave Properties Flashcards
What are mechanical and electromagnetic waves?
Mechanical waves are vibrations that travel through a medium, electromagnetic waves can travel through a vacuum and no medium is needed.
What are waves?
They are the transfer of energy from one place to another without the transfer of matter.
What are transverse waves?
When oscillations are perpendicular to the direction of energy transfer - EM waves.
Have peaks and troughs.
What are longitudinal waves?
When oscillations are parallel to the direction of energy transfer - e.g. sound waves.
Have compressions and rarefactions.
What is the amplitude of a wave?
The maximum displacement of a point on a wave from its undisturbed position. A bigger amplitude means more energy can be carried.
What is the wavelength?
It is the distance from a point on a wave to the equivalent point on an adjacent wave.
What is the frequency?
The number of waves passing a fixed point every second.
What is the period?
The time taken for a wave to completely pass a single point.
What is the equation for wave speed?
Wave Speed = Frequency x Wavelength
How can you find the velocity of sound?
To measure the velocity of sound in air, make noise 50m from a solid wall and record time to hear an echo, then use distance/time.
Describe method to investigate the water waves in a ripple tank.
- Fill ripple tank so that water has depth of around 5mm and place ripple tank on top of a screen.
- Place wooden rod on surface of the water and attach to a low voltage power supply and motor. Add lamp to the circuit and hold lamp above the ripple tank.
- View pattern from the side of the tank.
- To measure the wavelength, measure using a ruler the length of the screen and divide this distance by the number of wavefronts.
- Frequency can be recorded by timing how long it takes for a given number of waves to pass a particular point and divide the number of wavefronts by time taken.
- Calculate wave speed using wavelength x frequency.
How do waves reflect?
Reflected waves move away from the barrier at an equal angle to the incident waves. Waves reflect off smooth surface but rough surfaces scatter them.
How do waves refract?
Refraction occurs when a wave changes direction as it changes speed when it passes from one medium to another, frequency is unchanged.
If wave slows down, it refracts towards the normal. Deep to shallow = waves slow down.
If wave speeds up, it refracts away from the normal.
If wave front hits the same point at the change in medium, they do not change direction.
What is absorption and transmission?
Absorption = Material gains energy from waves and thermal energy store increases as a result of electrons absorbing light.
Transmission = Waves travel through a material.
What are the characteristics of sound waves and how do they cause sound?
- Sound waves cannot travel through a vacuum. Pitch of a sound increases if frequency of sound waves increases. Loudness of a sound wave increases if amplitude increases.
- Sound waves cause ear drums to vibrate, vibrations send signals to the brain. Object vibrating causes air to vibrate and send out vibrations of air in waves of compressions and rarefactions which reach the ear.
