6.2 Flashcards
What is the electromagnetic spectrum?
- Transverse waves.
- Transfer energy from source of wave to absorber.
- Don’t need medium to travel in - can travel in vacuum.
- All travel at same speed in vacuum
- Continuous spectrum
- Different materials interact differently with EM waves, depending on wavelength.
List the different waves in the electromagnetic spectrum in order of wavelength and frequency.
Increasing wavelength:
Radio wave, microwave, infrared, visible light, UV, X-ray, gamma
Increasing frequency:
Gamma, X-ray, UV, visible light, infrared, microwave, radio wave
[Describe how to] Construct ray diagrams to show how refraction of a wave at the boundary between two different media can affect the perception of the object.
- Draw incident ray from object to boundary of new medium.
- If the new medium is denser, the wave bends towards the normal as it slows down and therefore changes direction (opposite for less dense).
- Draw reflected ray away from the medium, as it speeds up, towards the observer.
- Draw a straight line from reflected ray to other side of new medium to show where image will be located.
What happens when a wave travels perpendicular to the normal into a new medium?
The wave does not change direction but still changes speed.
Use wave front diagrams to explain refraction in terms of the change of speed that happens when a wave travels from one medium to a different medium.
- When the first wavefronts start to move into the glass, those parts slow down.
- This causes the wavelength of that part of the wavefronts to decrease making the wavefronts go closer together.
- This causes the waves to change direction towards the normal.
- When the waves change medium again, they speed up and change direction away from the normal.
What happens when wavefronts approach a different medium along the normal?
The whole wavefront changes in speed at the same time, according to the density of the new medium, but they do not change direction.
Describe how changes in atom can take place when electromagnetic radiation is generated or absorbed.
Changes in atom:
1. When atoms are heated, it causes electrons to moved from one energy level to a higher one.
2. When the electrons return to their original level, it generates an electromagnetic wave (light).
Changes in nuclei:
1. Gamma rays can be emitted from radioactive nucleus, leaving the atom with less energy than initially.
Describe the hazards of ultraviolet, X-ray and gamma rays
UV: increase risk of skin cancer, cause premature aging of skin.
X-ray and Gamma: cause mutations of genes, increase risk of cancer.
Explain how radio waves can be produced and absorbed.
When electrons oscillate in electrical circuit, they produce radio waves.
2. The radio waves can be absorbed by an aerial causing the electrons in the current of the aerial to oscillate.
3. This can create an alternating current with the same frequency as the radio wave.
What are the uses of electromagnetic waves?
- Radio: transmit radio and terrestrial TV signals.
- Microwaves: heat food, space satellite communication.
- Infrared: electrical heaters, ovens (cook food) and infrared cameras.
- Visible: fibre optics communication.
- UV: energy efficient lightbulb, sun tanning.
- X-rays: detect bones, medical treatment
- Gamma: detect cancers, medical treatment
Why are radio waves suitable for its use?
Allows us to send radio waves very long distances around the Earth.
- Can travel long distances before being absorbed (e.g. by buildings and trees)
- Longer wavelength radio waves can spread out between hills.
- Can reflect off charged layer of particles in atmosphere.
Why are microwaves suitable for its use?
- Most foods have a lot of water molecules which absorb microwave energy, increasing temperature of food.
- Microwaves can travel through the earth’s atmosphere without being refracted or reflected.
Why is infrared suitable for its use?
Energy from infrared easily absorbed by objects (e.g. objects in room absorb infrared from electrical heater, heating up room).
Why is visible light suitable for its use?
Short wavelength means it can carry a large amount of information.
Why is UV suitable for its use?
- Short wavelength = carry more energy than visible light
- Requires less energy than light bulb - internal surface of bulb absorbes UV and converts it into visible light.
Why are X-rays and gamma rays suitable for their use?
- Both very penetrative so pass easily through body tissue.
- X-rays absorbed by bones so can see imaging.
What is a convex lens?
Symbol: vertical line with outwards facing arrows.
- Parallel rays brought to focus at principal focus.
- Central ray passes through lens without being refracted.
Dray ray diagrams to show the formation of an image by a convex lens.
- Draw ray line from top of object arrow through the centre of the lens without changing direction.
- Draw ray line from top of object arrow horizontally to lens.
- Pass second arrow through principal focus.
- Where the two ray lines meet is where the image appears.
What are the possible outcomes of an image from a convex lens?
- Real (ray lines meet/converge) or virtual (they do not meet at point/diverge).
- Inverted (upside down) .
- Diminished (smaller) or magnified (bigger).
What is the principal focus?
The point where all rays passing through a lens meet
What is the focal length?
The distance between the lens and the principal focus.
Draw a ray diagram to show how a convex lens can be used as a magnifying glass.
- Draw ray line from top of object arrow through the centre of the lens without changing direction.
- Draw ray line from top of object arrow horizontal to lens.
- Pass second arrow through principal focus.
- From where the first ray begins and the second ray touches the lens, draw two dotted lines going back until they meet - this is where the image is.
What is the formula to calculate magnification?
Magnification (x) = image size / actual size
Draw ray diagram to show how an image is formed by a concave lens.
- Draw ray line from top of object arrow through the centre of the lens without changing direction.
- Draw second ray line from top of object arrow horizontal to lens.
- Continue second ray line from lens, with dotted straight line starting from principal focus, and normal line continuing after lens.
4.The point where the dotted line and the first ray line meets is where the image appears.
Describe the properties of image always produced by concave lens.
- Virtual
- Upright
- Diminished
What is specular and diffusion reflection?
- Specular reflection: all light rays reflecting in single direction (on smooth surface; produces image)
- Diffusion reflection: light rays are scattered (on rough surfaces; don’t produce image)
Describe how the colour of an object depends on the wavelengths of light absorbed and reflected.
- When light hits an opaque object, the light rays reflected determine the colour of the object.
- When light hits a white object, all light rays are reflected - either transparent or translucent (depending on surface smoothness)
- When light hits a black object, all light rays are absorbed.
Describe the effect of viewing objects through filters or the effect on light of passing through filters
- When light passes through a filter, the light rays associated with the colour are transmitted.
- The transmitted rays hit the object and if they correlate with the colour of the object they will be reflected and shown (e.g. red filter hits magenta object which appears red - no blue present)
- If the transmitted rays do not correlate with colour of object, object will appear black.
