Heat energy flows from a warmer to a colder object
Thermograms use colour to show temperature, typically with colours white/yellow/red for the hottest parts and black/dark blue/purple for the coldest parts
Temperature is a measure of hotness on an arbitrary/chosen scale, to compare two objects, but heat is a measure of internal energy, measured on an absolute scale
A particle with a higher temperature has more kinetic energy
Specific heat capacity (SHC):
SHC is the energy (Joules) needed to increase an object's temperature by 1 degree C, measured in J/kg
energy transferred (J) = mass (kg) x SHC x temperature change (degrees C). The SHC of water is 4.2 J/kg
Specific latent heat (SLH):
SLH is the energy needed to melt/boil 1kg of a material
energy transferred (J) = mass x SLH
When an object changes state, the temperature remains constant because energy is needed to break the bonds
Types of energy transfer:
Conduction is the transfer of kinetic energy from one particle to another particle next to it
Convection is the transfer of energy through the air, as hot air rises, it cools and falls, to be replaced by more hot air from the heat source, creating a flow
Radiation is infrared radiation, an electromagnetic wave, and needs no medium to travel through
Types of insulation:
Air is a good insulator because it is a poor conductor: molecules are far apart so heat does not pass through it easily with conduction
Double glazing reduces energy loss by conduction; the gap between two panes of glass is filled with a gas (e.g. argon) or by a vacuum
Loft insulation (made from fibreglass, mineral wool or rock wool) reduces energy loss by convection/conduction; warm air rises and heats the ceiling, which warms the air in the loft. Since both the loft and house below are at the same temperature, no heat is transferred
Cavity wall insulation (made from insulation foam or fibreglass) traps air in the foam and insulates well, reducing energy transfer by convection or conduction
Shiny foil reflects back heat from the sun and reflects heat from the house back into the house, keeping it at a good temperature
Curtains at windows are also good insulators
Energy efficiency:
efficiency = useful energy output ÷ total energy input
Sankey diagrams show useful and wasted energy. Here is an example for a light bulb:
All objects that transfer energy lose some to the environment (e.g. by heat, sound)
Waves:
wave speed = frequency x wavelength
A labelled wave:
The electromagnetic spectrum:
Here are the types of radiation: - radio (Longest wavelength, lowest frequency, least energy) - microwave - infrared - visible - ultraviolet - x-ray - gamma ray (Shortest wavelength, highest frequency, most energy)
Refraction and diffraction:
Refraction happens when the wave enters a more dense medium and the wavelength increases, or vice versa
Diffraction is the spreading out of a wave as it passes through a gap and the effects are very noticeable in telescopes
A larger communications receiver is needed for waves with high wavelengths, like radio and microwave
Morse code:
Morse code uses dots and dashes, often short and long flashes of light, to represent letters, and is an example of a digital signal
Signal transmission:
Signals can be sent quickly using light, electricity, radio, or microwaves
There are advantages and disadvantages of each; if the wire can be cut, or if the signal is visible to others
Lasers:
Laser light has only one frequency, has low divergence (doesn't spread out much) and is in phase (the crests and troughs line up). They only produce a single colour (they're monochromatic) in a narrow beam
White light, however, is made up of different colours of different frequencies out of phase, and has high divergence
Lasers are used to read from a compact disk (CD): the surface of the CD has billions of small pits representing digital data. Laser light is shone onto the surface and the difference in reflection provides information for the digital signal
They can also be used for surgery, dental treatment, cutting materials, weapon guidance, laser light shows, and many others
Critical angle:
When light enters a different material, it is usually refracted
When passing from a more dense to less dense material, the angle of refraction is larger than the angle of incidence
When the angle of refraction is 90°, the angle of incidence is called the critical angle
If the angle of incidence is larger than the critical angle, the light is reflected, total internal reflection
Diagrams:
Optical fibres:
Optical fibres are solid glass tubes which carry light through total internal reflection, so no light leaves the tube. Some are coated to improve reflection
Telephone conversations and internet data can be transferred at the speed of light in glass, around 200,000 km/s
Endoscopes:
Endoscopes allow doctors to see inside a body. One set of optical fibres illuminates the inside of the body, and this reflected light passes up another set to an eyepiece/camera
Infrared radiation:
Infrared radiation absorption is affected by the object's properties; for example surface temperature, colour, and texture (e.g. shiny, dull)
Microwave radiation:
Microwaves can cause burns when absorbed by body tissue
They can pass through plastics and glass but are reflected by shiny surfaces
Cooking:
Microwave ovens use microwave radiation. It penetrates around 1cm into the food, and causes water/fat molecules to vibrate more, this energy heats the food
Conventional ovens use infrared radiation. It does not penetrate food very far, but the kinetic energy of all particles on the surface is increased, and like with microwave ovens, the energy is transferred to the inside through conduction
High frequency (short wavelength) waves transfer more energy. Microwaves have a wavelength of 1 mm - 300 mm. Mobile phones use longer wavelengths than microwave ovens; less energy is transferred
Microwave ovens have special glass in the door to reflect microwaves, as they can cause body tissue to burn with exposure
Microwave communication:
The transmitter must be in line of sight with the receiver; so aerials are usually on top of tall buildings or on towers
Satellites in orbit are used to relay information across the globe
Microwaves don't diffract (spread out) much, so signal may be limited
Infrared radiation can also be used in remote controls, and short distance data links between electronic devices
Digital and analogue signals:
Digital signals have two possible states: on (1) and off (0). Analogue signals can have a range of amplitudes
Analogue signals can suffer from interference when the amplitude slightly changes. Digital signals have less interference because the receiver only has to tell whether it's 0 or a 1
Carrier waves have a high frequency. Analogue signals are often added to this carrier wave
Multiplexing allows for multiple digital signals to be transferred at one time by combining them then separating them afterwards
Remote controls:
A remote control device transmits a coded digital infrared signal
A switchover from analogue to digital signal in the UK for radio and TV started in 2009. It allows for a greater choice of programmes, improved signal quality, being able to interact with the programme and interactive programme guides/subtitles
Radio refraction and interference:
Wireless technology is used by radio, television, laptops and mobile phones
Radio waves are refracted/reflected in the ionosphere in the atmosphere, there is less refraction at higher frequencies. They undergo total internal reflection, and reflect off water, allowing for the signal to be received from an aerial that is not in the line of sight
Communication satellites take 24 hours to orbit Earth
Radio waves are diffracted when they meet an obstruction
Earthquake waves:
There are two types of seismic wave which you need to know about:
P waves are longitudinal, can pass through solids and liquids, and travel through the Earth at 5-8 km/s. They are refracted by Earth's core
S waves are transverse, can only pass through solids, and travel through the Earth at 3-6 km/s
P waves can be used by scientists to calculate the size of Earth's core
S waves show that Earth's core is liquid, as they do not pass through it
Tan/burn:
Ultraviolet light causes a tan
Cells in skin produce melanin, a pigment that produce the tan
Ultraviolet light is filtered out more with darker skin
Using a sunscreen with high SPF (sun protection factor) increases time that can be spent in the sun without burning max. time to spend in sun = published normal burn time x sunscreen SPF
Ultraviolet radiation can also cause sunburn, skin cancer, cataracts and premature skin aging
Ozone layer:
Ozone is found in the stratosphere and helps filter out UV radiation
However, CFCs from aerosols and fridges destroy ozone in the ozone layer, increasing potential damage to humans. This was not originally known and the discovery of a reduction in ozone levels above Antarctica was unexpected
It is thinnest above the South Pole because ozone is best destroyed in cold conditions
The thickness of the ozone layer can be measured with satellites, there is an international agreement to reduce CFC emissions
