Waves Flashcards
What are transverse waves and examples of transverse waves?
In transverse waves, the oscillations (vibrations) are perpendicular (at 90°) to the direction of energy transfer.
- All electromagnetic waves
- Ripples and waves in water
- A wave on a string
What are longitudinal waves and examples of longitudinal waves?
In longitudinal waves, the oscillations (vibrations) are parallel to the direction of energy transfer.
- Sound waves in air, ultrasound
- Shock waves
All waves can be…
All waves can be absorbed, transmitted or reflected.
What is specular reflection?
Specular reflection is when a wave is reflected in a single direction by a smooth surface.
What is diffuse reflection?
Diffuse reflection is when a wave is reflected by a rough surface and the reflected rays are scattered in lots of different directions.
Why can electromagnetic waves travel through a vacuum?
Electromagnetic waves aren’t vibrations of particles, they’re vibrations of electric and magnetic fields.
List the electromagnetic waves in order of increasing frequency and decreasing wavelength.
Radio Waves Micro Waves Infrared Visible Light Ultraviolet X-rays Gamma Rays
How does a wave refract through a denser object?
Usually, the denser the material, the slower a wave travels through it. If a wave crosses a boundary and slows down it will bend towards the normal. If the wave is travelling along the normal it will change speed, but it’s not refracted.
About long-wave radio waves…
Long-wave radio (wavelengths of 1 - 10km) can be transmitted and received halfway round the world. This is because long-wave radio waves diffract (bend) around the curved surface of the Earth.
About short-wave radio waves…
Short-wave radio signals (wavelengths of about 10m - 100m) can also be received at long distances from the transmitter. That’s because they are reflected from the ionosphere - an electrically charged layer in the Earth’s upper atmosphere.
About microwaves in satellites…
Microwaves are able to pass through the Earth’s watery atmosphere. For satellite TV, the signal from a transmitter is transmitted into space where it’s picked up by the satellite receiver dish orbiting thousands of kilometres above the earth. The satellite transmits the signal back to Earth in a different direction where it’s received by a satellite dish on the ground. There is a slight time delay between the signal being sent and received because of the long distance the signal has to travel.
About microwaves in microwave ovens…
In microwave ovens, the microwaves need to be absorbed by water molecules in food - so they use a different wavelength to those used in satellite communications. The microwaves penetrate up to a few centimetres into the food before being absorbed and transferring the energy they are carrying to the water molecules in the food, causing the water to heat up. The water molecules then transfer this energy to the rest of the molecules in the food by heating.
What is optical density
The optical density of a material is a measure of how quickly light can travel through it - the higher the optical density, the slower light waves travel through it.
What are optical fibres and how do they work?
Optical fibres are thin glass or plastic fibres that can carry data over long distances as pulses of visible light. They work because of reflection. The light rays are bounced back and forth until they reach the end of the fibre.
What is fluorescence?
Fluorescence is the property of certain chemicals, where ultraviolet radiation is absorbed and then visible light is emitted.
