Light and the Electromagnetic Spectrum Flashcards
SP5a Ray diagrams
Explain the following;
A) Reflection
B) Refraction
A) When waves are reflected, the angle of reflection (r) is equal to the angle of incidence (i). This is called the law of reflection.
- These angles are measured from the normal line, a line perpendicular to the wave cross boundary.
B) Light travels at different speeds in different mediums, it travels faster in air than it does in glass or water. When light changes speeds this results in it changing directions. This is called refraction.
- When light meets an interface along the normal, the light ray does not change directions.
SP5a Ray diagrams
Explain Total Internal Reflection
- When light passes from water or glass into air with small angles of incidence, most of the light passes through the interface but some is reflected.
- As the angle of incidence increases, the angle of refraction also increases until the refracted ray is travelling along the interface.
- If the angle of incidence increases any further, the light is completely reflected inside the glass. This is called Total Internal Reflection & the angle this starts to happen at is called the critical angle.
SP5b Colour
Explain the differences between Specular and Diffuse reflection
- Most material have rough surfaces if you examine them closely, so the light is reflected in all direction, this is called Diffuse reflection
- Very smooth surfaces such as mirrors, reflect the light evenly. This is called Specular reflection
SP5c Lenses
Describe the following;
A) Converging Lenses
B) Divergent Lenses
A) A converging lens. is fatter in the middle than at the edges. It makes paralell rays of light converge ( come together ) at the focal point.
- The focal length is the distance between the focal point and the centre of the lens.
B) A diverging lens is thinner in the middle than at the edges. The focal point is the point from which the rays seem to be coming after passing through the lens.
The power of a lens depends on it’s focal length and its shape.
SP5c Lenses
Explain the effect of different types of lenses in forming real and virtual images.
- The kind of image formed by a coverging lens depends on where the object is. A converging lens can be used to focus rays of light onto a screen. ( this is called a real image & they can only be formed by rays of light that converge )
- A real image formed by a converging lens tends to be inverted and smaller than the object.
- An object close to a converging lens will form a virtual image. It is called virtual because it cannot be projected onto a screen. The image appears on the same side as the object, and is upright and magnified ( bigger ).
- Diverging lenses always produce virtual images that are the same way up, much smaller and closer to the lens than the object.
SP5d Electomagnetic waves
A) Provide an example of the fact that EM waves transfer energy from source to observer
B) Describe some facts about EM waves
A) We see things when light travels from a source and is reflected by an object into our eyes. The light transfers energy from the source to our eyes. Light is a type of EM wave.
- Our eyes can detect certain frequencies of light, and we refer to these frequencies as visible light. Different frequencies cause us to see different colours.
- Lower frequencies of visible light appear more red, while higher seem more blue.
B) All EM waves are transverse waves. Also all EM waves travel at the same speed in space.
SP5e The Electromagnetic Spectrum
Outline the EM spectrum
From the shortest wavelength & highest frequency:
- Gamma rays
- X-rays
- Ultraviolet
- Visible light.
- Infared
- Micro-waves
- Radio waves
SP5f Using the long wavelengths
Describe the different uses for the following EM waves;
A) Visible light
B) Infrared
C) Microwaves
D) Radio waves
A) Visible light is part of the electromagnetic spectrum that our eyes detect. Light bulbs are designed to emit visible light, while cameras detect it and record images.
B) Infared radiation can be used for communication at short ranges, such as between computers in the same room or from a TV to its remote control unit.
- A grill or toaster transfers energy to food by infrared radiation. The food absorbs the radiation and heats up.
- Security systems often have sensors that can detect infrared radiation emitted by intruders. Some buildings are fitted with systems of infrared beams and detectors, someone walking through one of these beams breaks and sets off the alarm
C) Microwaves are used for communciation and satellite transmissions, including mobile phone signals. In a microwave oven, microwaves transfer energy to the food, heating it up.
D) Radio waves are used for transmitting radio broadcasts and TV programmes as well as other communications. Some radio communications are sent via satellites. Controllers on the ground communicate with spacecraft using radio waves.
SP5f Using the long wavelengths
A) Describe how Radio waves are produced and detectedy
B) Describe how Radio & Microwaves react with the ionosphere
A) Radio waves are produced by oscillations ( variations in current & voltage ) in electrical circuits. A metal rod or wire can be used as an aerial to receive radio waves.
- These radio waves are absorbed by the metal and cause oscillations in electric circuits connected to the aerial.
B) Some frequencies of radio waves can be refracted by a layer in the atmosphere called the ionosphere. If radio waves meet the ionosphere at a suitable angle, they may be refracted enough to be sent back down to earth.
- Microwaves are not refracted in the Earth’s atmosphere.
- Ionosphere - A region of charged particles in the atmosphere.
SP5g Radiation and temperature
Describe the effect temperature has on body emitted radiation.
- The intensity ( amount ) of radiation emitted by an object increases as its temperature increases. The wavelengths of the radiation emitted also change with temperature - the higher the temp, the shorter the wavelength.
- For a system to stay at a constant temperature it must absorb the same amount of power as it radiates.
SP5g Core practical - Investigating radiation
Describe the core practical to investigate how different coloured surfaces absorb/radiate energy.
Aim - Investigate how the nature of a surface affects the amount of thermal energy radiated or absorbed
- A: Cover four or more boiling tubes in different coloured materials.
- B: Pour the same volume of hot water from a kettle into each tube.
- C: Insert a bung with a thermometer into each tube. Measure the temperature of the water in each tube and start a stop clock.
- D: Record the temperature of the water in each tube every 2 minutes for 20 minutes.
SP5h Using the short wavelengths
Describe the uses of Ultraviolet
- Ultraviolet radiation transfers more energy than visible light. The energy transferred can be used to disinfect water by killing microoragnisms in it.
- Some materials absorb ultraviolet radiation and re-emit it as visible light. This is called flouresence. Flourescent materials are often used in security markings - they are only visible when ultraviolet light shines on them.
- Many low energy light bulbs are flourescent lamps. A gas inside these lamps produces ultraviolet radiation when electric current passes through it. A coating on the inside of the glass absorbs the ultraviolet and emits visibile light.
SP5h Using the short wavelengths
Describe the uses of X-rays
- X-rays can pass through many materials that visible like cannot. E.g., they can pass through muscles and fat easily but bones absorb some X-rays.
- This means X-rays can be used in medicine to make images of the inside of the body. X-rays can also be used to examine the inside of metal objects and to inspect luggage in airport security scanners.
SP5h Using the short wavelengths
Describe the use of Gamma rays
- Gamma rays transfer alot of energy, and can kill cells. For this reason they are used to sterilise food and surgical equipment by killing potentially harmful microorganisms.
- Gamma rays are used to kill cancer cells in radiotherapy, they can also be used to detect cancer. A chemical that emits gamma rays is injected into the blood.
- The chemical is designed to collect inside cancer cells. A scanner outside the body then locates the cancer by finding the source of gamma rays.
SP5i EM radiation dangers
Describe the harmful effects of; microwaves and infrared radiation on the body
Microwaves:
- A certain microwave frequency can heat water and this frequency is used in microwaves.
- This heating could be dangerous as our body is mostly made of water and so the microwaves could heat cells from the inside.
Infrared radiation:
- Infrared radiation is used in grills and toasters as we cook food. Our skin absorbs, which we feel as heat. Too much infrared radiation can damage or destroy cells, causing burns to skin.
SP5i EM radiation dangers
Describe the harmful effects of ultraviolet & X-rays/Gamma rays on the body.
Ultraviolet:
- The energy transferred by ultraviolet radiation to our cells can cause sunburn and damage DNA. Too much exposure to ultraviolet radiation can lead to skin cancer.
- The ultraviolet radiation in sunlight can also damage our eyes. Skiers and mountaineers can suffer from temporary ‘snow blindness’ because so much ultraviolet radiation is reflected in the snow.
X-rays/Gamma rays:
- X-rays and gamma rays are higher frequency than ultraviolet radiation and so transfer more energy. They can also penetrate the body.
- Excessive exposure to X-rays and gamma rays can cause mutations in DNA that can kills cells or cause cancer.
SP5i EM radiation dangers
Describe how changes in atoms and nuclei affect radiation.
- EM radiation is produced by changes in the electrons or nuclei in atoms.
- For example, when materials are heated, changes in the way the electrons are arranged can produce infrared radiation or visible light. Changes in the nuclei of atoms can produce gamma radiation.
- Radiation can also cause changes in atoms, such as causing atoms to lose electrons.
