What are electromagnetic waves?
Transverse waves that all travel the same speed through a vacuum but different speeds in different mediums (travel at speed of light)
-they are made of oscillating electric and magnetic fields and do not need to particles or matter to travel
What is the electromagnetic spectrum?
They range from long wavelength (low frequency) to short wavelength (high frequency)
Radio waves, micro waves, infrared, visible light, ultra violet, x-rays, gamma rays
What effect do the first (lowest) 4 EM waves have on the human body?
- radio waves are transmitted through the body not absorbed
- some wavelengths of microwaves are absorbed causing heating of cells (which can be dangerous)
- infrared and visible light are mostly reflected or absorbed by the skin causing some heating too. Can cause IR burned if skin gets too hot
What effect either last (shorter) 3 EM waves have on the human body?
- High frequency can be dangerous as it is a type of ionising radiation - can cause skin cancer as absorbed by surface cells or cause blindness if in eyes
- X-rays and gamma rays are ionising so can cause mutations or cell damage (can cause cancer) can also be absorbed by deeper tissue
What is energy proportional to?
Frequency
- Hight frequency has more energy, low frequency has less energy
- EM waves transfer energy from a source to an absorber
What happens to an object as the temperature increase?
The intensity and distribution of every emitted wavelengths increases. This increases more rapidly for shorter wavelengths causing the peak wavelength (most intense) to decrease
-intensity is the power per unit area (power is energy transferred/sec)
Varying EM power affects the temperature of an object explain how power affect this?
- if the average power that an object absorbs is less than the average power that it radiates the object heats up. Vice Versa
- an objects at a constant temperature radiates and absorbs the same average power
How can radiation affect the earth’s temperature?
-if the atmosphere starts to absorb more radiation without emitting the same amount the over temperature will rise until absorption and emission are equal again (global warming)
How can we produce and detect radio waves?
- a.c. is made up of oscillating electric and magnetic fields (EM waves)
- the frequency of the waves produced will be equal to the AC
- A receiver absorbs this and the energy is transferred to the electrons
- this causes the electrons to oscillate generating an alternating current equal to the supplied AC
What are some uses of long radio waves?
Long wave radio bend around the surface of the earth making it possible for radio signals to be received even if the receiver isn’t in line of the transmitter
They can also be refracted by the ionosphere
What are some uses of shortwave radio?
- They can be reflected by the earth’s atmosphere so can be received through a transmitter over long distances e.g. Bluetooth
- radio waves for TV or FM are very short so to get reception you must be in direct sight of the transmitter
How are microwaves used for communication?
- they can pass daily through the earth’s watery atmosphere and detected by orbiting satellites
- the satellite then transmits the signal back to earth in a different direction where it can be receiver by a satellite dish
How are microwave ovens used?
- microwaves penetrate a few centimetres into food before being absorbed and transferring their energy to the water molecules causing the water to heat up
- the water molecules than transfer this energy to the food -heating it
Who and how discovered infrared?
Hershel discovered their was invisible light below red (infrared) as there was a continual temperature change beyond the visible light spectrum
How can infrared transfer information?
- used to send files between phones and laptops but the receiver must be in line if sight if the emitter
- can be used as a TV remote
- optical fibres can carry data over long distances as pulses of infrared by used a single wavelength prevent dispersion and loss of information
How can infrared be used to monitor or increase temperature?
- infrared cameras can be used to detect infrared radiation p/monitor temperature as the camera detects IR radiation and turns it into electrical signal, displaying it as thermal imaging (can be used by the police to see suspects in the dark)
- food can be cooked by as it heats up as it absorbs IR radiation
What are the uses of visible light?
- photographic film reacts to light to form an image
- digital cameras contain image sensors which detect visible light and generate electrical signals which are converted into the image
What are the uses of ultraviolet?
- Fluorescence where UV radiation is absorbed and the visible light is emitted (e.g in fluorescent lights)
- security pens under UV light will glow -illuminating writings
- can be sued to detect forgery in banknotes or passports as they have special markings that inky shoe up under UV light
- can be used to sterilise water
What are some used of X-rays?
- used in airport security scanners to detect hidden objects
- X-ray imaging is when the X-ray is directed through the object or body -the brighter bits mare where fewer X-rays get through producing a negative image
- radiographer take X-ray images to diagnose broken bones as they are transmitted by flesh but absorbed by bone
What are gamma rays used for?
- to sterilise medical instruments and food (meaning they can be preserved) as they kill microbes
- medical imaging such as tracers that can detect cancer
- cancer treatment such as chemotherapy
What does colour and transparency depend on?
The absorbed wavelengths and weather they are transmitted, absorbed or reflected
What is white light?
A mixture of all the different colours of light which all have different wavelengths. They reflect all wavelengths of visible light equally
What are black objects?
They absorb all wavelengths of light so there is an absence of colour
How do opaque objects work?
- do not transmit light but rather absorb or reflect some wavelengths
- the colour of the object depends on which wavelengths of light are reflected or which colours have mixed (red, blue and green don’t mix)
