What type of waves are electromagnetic waves?
Transverse waves, they travel as vibrations through magnetic and electric fields, with vibrations perpendicular to the direction of energy transfer
What are wavefronts?
Surface containing points affected in the same way by a wave at a given time
What is the angle in which waves reflect at, from hard flat surfaces?
- Straight waves directed at a certain angle to a hard flat surface, reflect off at the same angle.
- Angle between the reflected wavefront and surface is the same as the angle between incident wavefront and the surface
What occurs when waves pass across a boundary in which wave speed changes?
- When waves pass across a boundary at which the wave speed changes, the wavelength also changes
- If wave fronts approach at an angle to the boundary they change direction as well as changing speed
What happens if waves approach a boundary at which the wave speed changes, at an angle?
- If wave fronts approach at an angle to the boundary they change direction as well as changing speed
- This effect is known as refraction
When does diffraction occur?
Diffraction occurs when waves spread out after passing through a gap or round an obstacle
How does gap size affect diffraction?
- The narrower the gap the more the waves spread out
* The longer the wavelength, the more the waves spread out
Why are waves diffracted?
- Each point on a wavefront is a secondary emitter of wavelets
- Wavelets from the points along a wavefront travel only in the direction in which the wave is travelling
- Not in the reverse direction
- Combine to form a new wavefront spreading beyond the gap
What happens if the gap is bigger than the wavelength?
Diffraction is unnoticeable
When does noticeable diffraction occur?
When the gap is several wavelengths wide
When do you get the most diffraction?
When the gap is the same size as the wavelength
What happens if the gap is smaller than the wavelength
Waves are mostly reflected back
What is required to observe a clear diffraction pattern?
You need to use a monochromatic coherent light source
What is intensity?
Power per unit area
Why are satellite TV dishes pointed south?
• Because satellites orbit the earth directly above the equator, the larger the dish the stronger the signal it can receive.
Why does dish size affect how strong of a signal it can receive?
- Bigger the dish the stronger signal it can receive
- More radio waves are reflected by the dish onto the aerial, but a bigger dish reflects the radio waves to a smaller focus, because it diffracts waves less
- Bigger dish needs to be aligned more carefully than a smaller dish otherwise it will not focus the radio waves onto the aerial
