Waves (electromagnetic, lenses, light and black body radiation) Flashcards
What electromagnetic waves and their features?
transverse waves that transfer energy from the source of the waves to an absorber
- all electromagnetic waves travel at the same velocity (the speed of light) in the air or a vacuum
order the different types of electromagnetic waves from the lowest to the highest frequency?
radio, microwaves, infrared, visible, ultraviolet, x-rays, Gamma
How are signals created?
radio waves can be produced by oscillations in electrical circuits
when radio waves are absorbed, they cause electrons in the circuit to oscillate
this creates an alternating current with the same frequency as radio waves - this is how the signal is received
what happens when electromagnetic waves are being generated or absorbed?
changes in atoms and the nuclear of atoms occur
How can waves be generated?
by electrons moving between energy levels, as a result, of heat or electrical excitation can generate waves
i.e. an unstable nucleus can give out excess energy as gamma rays
Why are ultraviolet waves, x-rays and gamma rays harmful?
because they transfer a lot of energy
What damages could UV waves cause?
- cause the skin to age prematurely
- increase the risk of skin cancer
What damages can X-rays and gamma rays cause?
damage cells by ionising atoms and if absorbed by the nucleus o the cell. can cause gene mutations and cancer
What are the units of radiation dose and what does it measure?
sieverts ad is a measure of the risk of harm resulting from an exposure of the body to radiation
What are the uses of radio waves and why?
- television, radio and Bluetooth
this is because radio waves are low energy waves and therefore, not harmful, making them ideal for radio transmissions
are able to be reflected from the ionosphere = allows us to send radio waves very long distances around the Earth
able to travel long distances without being absorbed by buildings or trees
longer wavelength radio waves can also spread out between hills
What are the uses of radio waves and why?
- Satellite communications, cooking food
Microwaves travel in straight lines through the atmosphere, can pass through without being reflected or refracted = good for transmitting signals to satellites in orbit and transmitting them back down to receivers
for heating food, water molecules in food absorb the energy from microwaves, which causes the temperature of the food to increase
What are the uses of infrared waves and why?
- Electrical heaters, cooking food, infrared camera
- energy of infrared is easily absorbed by the surface of objects
- electrical heaters etc glow red hot as the electricity flows through them
What are the uses of visible waves and why?
- Fibre optic communications
- visible light travels down optical fibres from one end to the other without being lost through the sides
- has a short wavelength, can carry a lot of information ( fire optics used to carry telephone and cable TV signals)
What are the uses of UV waves and why?
- Energy-efficient light bulbs, security marking, sunbeds
- Ultraviolet has a short wavelength and carries more energy than visible light
- In energy-efficient bulbs, UV waves are produced by the gas in the bulb when it is excited by the electric current.
These Uv waves are absorbed by the coating on the bulb, which fluoresces giving off visible light
this requires less energy than a normal light bulb
What are the uses of X-rays waves and why?
Medical imaging and treatments
- X-rays are able to penetrate soft tissue but not bone. A photographic plate behind a person will show shadows where bones are
What are the uses of Gamma waves and why?
Medical imaging, tracer, Sterlising food, treatment of tumours,
- Gamma rays are the most energetic = used to destroy bacteria and tumours
- gamma emitting source is injected into the patient and its progress is followed around the body. gamma can pass out of the body
What is a convex lens?
What happens in a convex lens?
lens that curves outwards
rays of light are brought to a focus at the principal focus.
What is the focal length?
The distance from the lens to the principal focus
Why doesn’t the middle ray get refracted?
because it is normally incident onto its surface
What is a concave lens?
What happens in a concave lens?
lens that curve inwards
parallel rays of light entering the lens spread out, this makes the rays of light appear to have come from the principal focus on the same side of the lens they have originated
What type of images do convex lenses?
What type of images do concave lenses?
real or virtual
only virtual
What is a real image?
on the opposite side of the lens to the object can be projected onto a screen
lens come together
What is a virtual image?
on the same side as the object and can only be seen by looking through the lens
lens dont come together
equation for magnification
image height/ object height
How to make a lens more powerful?
- making the focal length more powerful
- make the lens more curved
- use different material that naturally refract light strongly
What happens to the image when an object is more than 2 focal lengths from the convex lens?
- image is diminished
- inverted
- the image is real
What happens to the image when an object is between 1-2 focal lengths from the convex lens?
- magnified
- inverted
- real
describe what happens to light when it passes through a lens
it refracts :
the light bends towards the normal when it passes into the lens
then away when it passes out of the lens
What happens to the image when an object is reflected by a concave lens?
- diminished
- right way up
- virtual ( rays do not meet at the principal focus)
What happens to the image when an object is closer to the lens than the focal length for a convex lens?
- virtual image
- magnified
- right way up
this is why convex lenses are used as magnifying glasses
