P2 Flashcards
Energy transfer by heating
Describe the method for a practical investigating different conductivities of different materials
- gather equipment
[] 5 identical glass beakers (300ml)
[] kettle
[] lids for each beaker with a hole for the thermometer
[] thermometer
[] timer
[] 4 different materials (newspaper, bubble wrap, foam, cloth) - ALL SHOULD BE OF THE SAME MASS - wrap each material around one beaker, leaving one uncovered
[] make sure to cover the bottoms of the beakers as well to reduce conduction to the work surface - in one beaker, pour 250cm^3 of just-boiled water and quickly put the lid with thermometer on
[] the bulb of the thermometer must be in the water - wait for the water to reach a maximum temperature, then begin the timer
- record the start temperature of the first beaker
- check and record the temperature every three minutes over 15 minutes total
- repeat with the other 4 beakers
- plot cooling curves for each beaker and label which had which material
Describe the method to investigate the relationship between the thickness of the thermal insulator used and loss of heat
- gather equipment
[] 5 identical beakers (300ml)
[] bubblewrap or newspaper
[] timer
[] lid for each beaker with a hole for thermometer
[] thermometer
[] kettle + water - prepare each beaker
[] one w/no bubblewrap
[] one w/two layers
[] one w/four layers
[] one w/six layers
[] one w/eight layers
[] MAKE SURE TO COVER BOTTOMS AS WELL - pour 250cm^3 of just-boiled water in one flask and cover with lid and thermometer, making sure the bulb is inside the water
- wait for it to reach a maximum temperature before starting the timer
- start the timer and record the start temperature of the water
- measure and record the temperature every three minutes over 15 minutes total
- repeat with the other four beakers
- plot cooling curves for each beaker on a graph with temperature on the y-axis and time on the x-axis
What is thermal conductivity ?
How well a material conducts (transfers) thermal energy
What does the quality of insulation of a material depend on ?
- thermal conductivity
- thickness/no. of layers of the material used
- temp. difference across the material
What absorbs/emits infrared radiation ?
everything
How does temperature affect emission of infrared radiation ?
higher temp = more emission, whilst lower temp = less emission
What colour/surface is the best at both emitting and absorbing infrared radiation ?
matte black
What is black body radiation ?
infrared radiation emitted from a perfect black body (perfect black bodies are the best possible emitters and absorbers of infrared)
What is the relationship between an object’s temperature and the range of wavelengths of radiation it emits ?
An object with a constant temperature emits radiation across a continuous range of wavelengths
What is a perfect black body ?
an object that is the best possible absorber and emitter of radiation
- ABSORBS ALL INCIDENT RADIATION
How does the temperature of an object increase/decrease ?
absorbing/emitting more infrared radiation than it emits/absorbs
What does the Earth’s temperature depend on ?
rate of absorption and emission of infrared radiation from the sun into Earth/the atmosphere/space
What is specific heat capacity ?
The total energy needed to raise 1kg of a substance by 1 degree celsius
What is the unit for specific heat capacity ?
J/kg*C
Give the equation for specific heat capacity
SHC = energy/(mass x change in temperature)
What is water’s specific heat capacity ?
4200 J/kg*C
Describe the method to a practical investigating the specific heat capacity of aluminium
- gather equipment
[] mass balance
[] aluminium block (with hole for immersion heater and thermometer)
[] immersion heater
[] joulemeter
[] insulating material like foam or bubblewrap
[] thermometer - using the mass balance, measure and record the mass of the aluminium block
- put the block in the insulator and insert the thermometer
- record the start temperature of the block
- connect the immersion heater to the joulemeter and connect the joulemeter to the power supply, then turn it on
- wait 5 minutes
- record the total energy supplied by reading the joulemeter’s display
- record the end temperature and calculate the change in temperature
- use the equation SHC = e/m x Δtemp to work out aluminium’s specific heat capacity
What does a storage heater do ?
uses electricity off-peak (at night) to heat concrete blocks in the heater, which then store a lot of thermal energy due to their high heat capacity and release it slowly during times of peak electricity use
What is loft insulation and how does it reduce transfer of thermal energy out from the roof ?
- thick fibreglass layers between the roof and the loft ceiling
[] fibreglass has a very low thermal conductivity so refuces energy transfer through the roof
What is cavity wall insulation and how does it reduce transfer of thermal energy out from the roof ?
- reduces rate of energy transfer through outer walls of the building
- insulation pumped into the space between the two walls (double walls)
How is aluminium foil used between a radiator and a wall to reduce heat loss from the house ?
reflects radiation away from the wall so that it cannot pass out of the house but into it
What are double-glazed windows and how do they insulate a house ?
- windows with two panes of glass with a vacuum between them
[] vacuum prevents energy transfer by convection
[] sometimes dry air is used instead as it is a good insulator (reduces energy transfer by conduction) - thicker + lower thermal conductivity glass slows rate by conduction
How do thick outer bricks help to insulate a house ?
thicker + lower thermal conductivity bricks means slower heat loss from the house to outside
Why is insulation important in buildings ?
reduces heating costs
What are used to heat houses ?
- electric/gas heaters
- gas/oil-fired central heating
- solid fuel stoves
