Energy Transfer by Heating
Infared radiation (emitted by solids,liquids and gases)- All objects emit and absorb heat, the hotter the object, the more IR radiation it emits. IR radiaton can travel through a vacuum as it involves waves rather than particles. IR radiation depends on colour and texture, light, shiny surfaces are poor emitters and abosrbers as they reflect the heat. Whereas, dark, matt surfaces are good emitters and absorbers.
Conduction (solids)- When a solid is heated, it's particles gain more energy and bump into other particles causing them to heat up and gain more energy. They then vibrate and bump into particles- this passes the thermal energy from the hot end to the cold.
Metals are good conductors as they have free electrons so the particles can move faster and more freely.
Convection (liquids/gases)- Convection occurs when particles with a lot of thermal energy take the place of particles with less thermal energy. This is because the hot particles rise due to their low density, and colder, more dense particles fall.
Kinetic Theory- The Kinetic Theory describes how particles move in liquids, solids and gases.
- Solid: Particles are close together in a regular pattern and vibrate around a fixed position.
- Liquid: Particles are close together in a random pattern and move around each other.
- Gas: Particles are far apart and random and they move freely in any direction.
Condensation- Gas to liquid (high density, low temperature, less airflow)
Evaporation- Liquid to Gas (low density, high temperature, great airflow)
Rate of Heat Transfer
The rate of heat transfer depends on-
- Surface area- Heat energy is radiated from the surface of an object, the bigger the surafce area, the more IR waves it emits, so the quicker the transfer of heat.
- Material used
- Temperature of surface- if the surface is cold, the object will emit heat faster, if the surface is warm, the object will absorb heat faster. If the surface is similar to the object, the change will be gradual.
Controlling Heat Transfer-
- Human's- The hair on our skin stands up when it is cold to create a thick layer of insulating air which limits of the heat loss by convection. When we are too warm, the blood rushes to our skin so heat can by lost by radiation.
- Artic foxes: small ears to minimise radiation due to their small surface area.
U-Values- show how fast heat can transfer through a material (lower the U-value, better insulator)
The most effective method of insulation (cavity wall, double glazing etc) are the ones that give you the biggest annual saving.
Eventually, the money you saved will equal the money you spent (payback time).
Payback time= Cost of insulation / savings per year
Specific Heat Capacity-
Heat and temperature are not the same thing:
Heat- a measure of themal energy in an object (J)
Temperature- a measure of how hot something is (°C)
The more heat energy transferred to an object, the greater the temperature increase.
The specific heat capacity of a substance is the amount of energy needed to change the temperature of 1 kg of the substance by 1°C.
Formula: E = m × c × θ
- E is the energy transferred in joules
- m is the mass of the substances in kg
- c is the specific heat capacity in J / kg °C
- θ (‘theta’) is the temperature change in degrees Celsius, °C
Forms of Energy
Energy cannot be created or destroyed, only transferred. The types are-
- Gravitational Potential
- Elastic Potential
A device is efficient when it maximises the amout of output energy that is useful.
Formula: Efficiency= Useful Output Energy / Total Energy
(Sankey Diagram on the back)
Electrical Energy Calculations
The amount of electrical energy transferred to an appliance depends on its power and the length of time it is switched on.
Formula: E = P × t
- E is the energy transferred in kilowatt-hours, kWh
- P is the power in kilowatts, kW
- T is the time in hours, h.
Cost of Electricity-
total cost = number of units × cost per unit
Boiler (Thermal) - Turbine (Kinetic) - Generator (Electrical)
Extra neutron makes Uranium235, Uranium236 - Atom splits, releases energy - Energy heats water turning into steam - Steam spins turbine - Turbine powers generator
- Wind- Wind turns a turbine which powers a generator
- Wave- Wave's kinetic energy drives turbine which powers a generator
- Geothermal- Hot water/steam from underground drive turbines which power generators
- Solar Cells- Coverts light energy into electrical energy
The National Grid distrubutes electricity from power stations to buildings-
- 1)Step-up Transformer (increases voltage to reduce energy loss along power line)
- 2)Electricity travels along high-voltage transmission lines
- 3) Step-down Transformer (decreases voltage so it is safe for use)
- 4) Consumer Usage
Waves- Vibrations that transfer energy without matter
Transverse Waves- The vibrations move perpendicular to the direction of the wave (up and down)
All Electromagnetic waves are transverse
Longitudinal Waves- The vibrations move parallel to the direction of the wave (side to side)
Seismic waves and Ultrasound waves and longitudinal
- Amplitude- The distance between the peak and rest line or trough and rest line. (big amplitude, loud sound)
- Wavelength- The distance between two matching points on neighbouring waves.
- Frequency- Number of waves passing any point each second (Hz) (High frequency, high pitch)
Formula: v = f × λ
- v is the wave speed in metres per second, m/s
- f is the frequency in hertz, Hz
- λ (lambda) is the wavelength in metres, m.
Refraction, Diffraction, Reflection and EM Waves
Refraction- When a wave crosses a boundary between two substances it changes direction.
If the second substance is denser than the first, it wil bend towards the normal (slower). Whereas, if the substance is less dense, it will bend away from the normal (faster).
Diffraction- When a wave spreads out when it crosses a gap/obstacle.
The narrower the gap, or the longer the wavelength, the more the waves spread out.
Reflection- Reflection of light is what allows us to see things.
Smooth surfaces produce clear reflections as it is reflected at the same angle. Whereas reflecting light on uneven surafces will make the light reflect off at different angles.
Law of Reflection: Angle of Incidence= Angle of Reflection
There a 7 types of EM waves that are grouped into the Electromagnetic Spectrum (long-short):
Radio (communication), Micro (mobile phones), Infared (remote controls), Visible Light (photography), Ultraviolet (Disinfecting Water), X-rays (Medical X-Rays) and Gamma Rays (Treats Cancer).
EM waves with higher frequencies have shorter wavelengths.
The Big Bang
According to this theory, all of the matter and space in the universe was compressed into a very small space and then it exploded and started expading, like it is today. The Big Bang is estimated to have happned 14 billion years ago. The 'Steady State' theory says that the universe has always existed as it is now and always will. However, discovery of the cosmic microwave background radiation (CMBR) was strong evidence that the Big Bang was more likely. Scientists have detected low frequency electromagnetic radiation from all parts of the unvierse (known as CMBR) which the Big Bang theory explains as just after the Big Bang the universe was extremly hot and emitted high frequency radiation, as it expanded, it cooled this radiation had dropped in frequency and is now seen as microwave radiation.
Light from other galaxies is red-shifted- we can see the same patterns but at lower frequencies as it is far away (the Doppler Effect). The further away the galaxy is, the greater the red-shift.
When something tht emits waves moves away or towards you, the wavelengths and frequencies seem different when they are, in fact, the same.
- 1) Source moving away- Frequency seems higher and wavelength shorter.
- 2) Source moving towards you- Frequency seems lower and wavelength longer.