Please enable JavaScript.
Coggle requires JavaScript to display documents.
Energy Transfer by Heating - C2, ΔE = mcΔθ - Coggle Diagram
Energy Transfer by Heating - C2
Conduction
Conduction mainly occurs in solids
Conduction is the process of vibrating particles transferring energy to neighboring particles
Energy transferred to an object by heating is held in the thermal store - this energy is shared across the kinetic energy stores of the particles in the object
The particles in the part of the object being heated vibrate more and collide with each other
These collisions cause the energy to be transferred between a particles kinetic energy stores in a process called conduction
This process occurs throughout the object until the energy has reached the other side of the object where it is then released into the thermal energy stores of its sorroundings
Thermal conductivity is a measure of how quickly energy is transferred through a material in this way
Materials with a high thermal conductivity transfer energy between their particles quickly
Convection
Convection only occurs in liquids and gases
Convection is where energetic particles move away from hotter to cooler regions
Energy is transferred by heating to the liquid or gas
It is stored in the kinetic energy store of the object
Unlike solids, the particles in liquids and gases are able to move - When a liquid or gas is heated, particles move faster and the space between particles increases - this causes the density of the heated region to decrease
Because liquids and gases can flow, warmer, less dense regions rise above the cooler ones
If there is a constant heat source, a convection current can be formed
Radiators Create Convection Currents
Heating a room with a radiator relies on convection currents
Energy is transferred from the radiator to the nearby particles through conduction
This air becomes warm and rises above the cool air which then sinks down
This cool air is then heated and rises - at the same time the previously heated air particles transfer energy to their surroundings, cooling it and therefore sinking
This cycle repeats, causing a circulation of air around the room - this is a convection current
Infrared Radiation
Every object absorbs and emits infrared radiation regardless of temperature
If an object has a constant temperature, then the object absorbs and emits infrared radiation at the same rate
If an object absorbs radiation faster than it emits it, then the objects temperature is rising
If an object emits radiation faster than it absorbs it, then its temperature is decreasing
Rescuers use light-coloured, shiny blankets to keep accident survivors warm
This is because these light, shiny surfaces emit much less radiation than a dark, matt surface
The patient is therefore kept much warmer
Radiation and the Earth's Temperature
The temperature of the Earth depends on many factors such as the rate that light and infrared radiation from the sun are:
Reflected back into space or absorbed by the Earth's atmosphere or by the Earth's surface
Emitted from the Earth's surface and from the Earth's atmosphere into space
If the Earth had no surface, temperatures would plunge to -180⁰C at night (The same as the moons surface at night)
This would occur because the surface would not be receiving any radiation from the sun
Some gases in the atmosphere such as water vapour, methane, and carbon dioxide absorb longer wavelength infrared radiation from the Earth and prevent it from going out into space
This makes the Earth warmer
Specific Heat Capacity
Specific Heat Capacity basically means how hard something is to heat up
More energy needs to be transferred to the thermal energy store of and object to heat it up than others
Materials that need to gain lots of energy in their thermal energy store to heat up, also have to lose a lot of energy to cool down
Specific heat capacity is the amount of energy needed to raise the temperature of 1kg of substance by 1⁰C
Equation that links energy transferred to specific heat capacity:
ΔE = Change in thermal energy (J)
m = Mass (kg)
C = Specific Heat Capacity (J/kg⁰C)
Δθ = Change in temperature (⁰C)
Δ means 'change in'
Investigating Specific Heat Capacities (Practical)
To investigate a solid material (copper) you need a block of that material with two holes in it (For heater and thermometer)
Measure the mass of the block and then wrap it in a layer of insulation (newspaper) to reduce the energy transferred to its sorroundings
Insert the thermometer and heater and measure the initial temperature of the block
The the potential difference (V) of the power supply to be 10V, then turn it on and start a stopwatch
When the power is turned on, the current in the circuit does work on the heater, transferring energy electrically to the heaters thermal energy store
This energy is then transferred to the materials thermal energy store by heating, causing the materials temperature to increase
As the block heats up, take temperature and current readings every minute for 10 minutes - the current shouldn't change while the temperature increases
1 more item...
Heating and Insulation
Lubrication Reduces Frictional Forces
Whenever something moves, there is usually one frictional force acting against it
This can cause some energy to dissipate - e.g. air resistance can transfer energy from a falling objects kinetic energy store to its thermal energy store
For objects that are being rubbed together, lubrication can reduce friction between surfaces
Lubrications are usually liquids such as oils that easily flow between objects and coat the
Insulation reduces the rate of energy transfer between by heating
Insulation is used because people do not want the heat from their houses to be lost into the outside
There are multiple methods of insulation
Have thick walls made from a material with low thermal conductivity
Thicker walls will lower the thermal conductivity and slow the rate of energy transfer so the building will cool slower
Use thermal insulation such as:
Cavity walls are made up of inner and outer walls with an air gap in the middle
The air gap reduces energy transferred by conduction through the walls
Cavity walls also have a version in which cavity walls are filled up with foam to reduce energy transfer by convection
Loft insulation can reduce convection currents being created in lofts
Double glazed windows work similarly to cavity walls
They have an air gap between two sheets of glass to prevent energy transfer through conduction
Draught excluders around doors and windows reduce energy transfer through convection
Investigating Effectiveness of Materials as Thermal Insulation
1) Boil water in a kettle then pour some of the water into a sealable container to a safe level - then measure the mass of the water in the container
2) Use a thermometer to measure the initial temperature of the water
3) Seal the container and leave it for five minutes - measure this time using a stopwatch
Remove the lid and measure the final temperature
Repeat this experiment but wrap the container in foil, newspaper, etc. Make sure to use the same mass of the water and the same initial temperature
The lower the temperature difference, the better a thermal insulator that material is - materials such as bubble wrap and cotton wool are good thermal insulators
This can also be done to measure how thickness of an insulator affects its insulation by wrapping multiple layers of each material and comparing them
ΔE = mcΔθ