What is a similarity and difference between reflection and refraction?
- Refraction and reflection both involve a change in direction and both occur at a boundary
- Refraction involves a change in speed and reflection does not. Reflected waves travel in the same material and refracted waves can travel in a different material or in the same material if it has different physical properties e.g. water of different depths; solutions of different densities
What is the wave equation?
wave speed = frequency x wavelength
What are similarities and differences or transverse and longitudinal waves?
- Both transfer energy / information without transferring matter
- The vibrations ar perpendicular to the direction of energy transfer in transverse and parallel in longitudinal
A student uses a rope, fixed at one end, to demonstrate transverse waves. A knot is tied at the midpoint of the rope. One end of the rope is fixed and the student can move the other end of the rope. Describe how the displacement of the knot changes during one complete cycle, starting from its equilibrium position
- The knot over vertically upwards from its equilibrium position to its maximum positive displacement (after 1/4 of a cycle)
- Then down through the equilibrium position (after 1/2 a cycle)
- Continuing down to its maximum negative displacement position (after 3/4 of a cycle) and back the equilibrium position after one complete cycle
Describe how you could use a slinky spring to demonstrate transverse waves
- Lay the spring flat on the table
- Move the end of the springs sideways, perpendicular to the length of the spring
Describe how you could use a slinky spring to demonstrate longitudinal waves
- Lay the spring flat on the table
- Move the end of the spring back and forwards along the length of the spring
How could you show that light os a transverse wave?
- Transverse waves can be polarised but longitudinal ones cannot
- Either show that light cannot pass through crossed polaroids, or that the intensity of unpolarised light is less once it passes through a single polarising filter
How do the properties of microwaves make them suitable for cooking?
They are strongly absorbed by fat and water molecules which makes them vibrate; this random vibrational energy is thermal energy in food
How do properties of microwaves make them suitable for satellite communication?
-Microwaves which are used for communication are chosen so that they are not absorbed by the water in the atmosphere and they are of a different wavelength to the microwaves used in ovens which are absorbed by water in the atmosphere Information encoded into the microwaves so that they carry information.
How does the alignment of TV ariels affects the strength of the signal received?
TV transmissions are usually polarised electromagnetic waves and the ariel must match the plane of polarisation of the electric field of the wave for maximum intensity
What are some uses of everyday polarising filters?
- An everyday use of polarising filter is in a polarising camera lens or in sunglasses as the polarising filter is orientated to block horizontally polarised reflections off surfaces such as water or snow
- In flat screens/liquid crystal displays to allow selective transmission of light
What is a progressive wave?
A wave that travels through a substance or space, transferring energy
What is the amplitude of a wave?
The maximum displacement from the undisturbed position
What is the wavelength of a wave?
The distance between the wave peaks (they may give the distance between half a wavelength so make sure double it)
What is the frequency of a wave?
The number of cycles per second, measured in Hz
What is a period?
The time for one complete cycle, measured in seconds
What is a hertz?
The unit of frequency, equivalent to s-1
What does ‘in phase’ mean?
- Particles along a wave that move in phase move:
1. In the SAME DIRECTION with the SAME SPEED
2. The particles have the SAME DISPLACEMENT from their mean position
3. Particles, in phase are SEPARATED by a WHOLE NUMBER, n of WAVELENGTHS, nlamda
What does ‘out of phase’ mean?
Particles along a wave that move out of phase are at different points in their cycle at a particular time
What does ‘anti phase’ mean?
- Particles along a wave that move in anti phase move:
1. In OPPOSITE DIRECTIONS at the SAME SPEED
2. The particles have OPPOSITE DISPLACEMENTS from their mean position
3. Particles moving in anti phase are separated by a distance of a WHOLE NUMBER, n of WAVELENGTHS plus an extra HALF wavelength, nlamda + lamda/2
What is a phase difference?
- A phase difference is measured as a fraction of the wave cycle between two points along a wave, separated by a distance x
- phi = 2pix/lamda rad
- One complete rotation involves turning through 2pi radians
- When a wave is reflected off the surface of a denser medium, it undergoes a phase change of 180 degrees
1. If two points say P and Q are both at the point of no disturbance and are half a wavelength separated their phase difference is 180 degrees
What is a longitudinal wave?
- In longitudinal waves particles vibrate parallel to the direction that energy travels in
- Example: sound waves
What is a transverse wave?
- In transverse waves vibrations are at a right angles to the direction that the energy travels in
- Example: EM waves
What is an electromagnetic wave?
Electromagnetic waves are transverse waves all of which travel at the speed of 3x108 mpersecond in a vacuum
