P1 - Energy Flashcards
What is energy transferred between?
Stores -
Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear energy stores
What happens when a system changes?
Energy is transferred
A system is just a fancy word for a single object (e.g. the air in a piston) or a group of objects (e.g. 2 colliding vehicles) that you’re interested in
What are closed systems?
Systems where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always 0
Energy can be transferred by which 2 methods?
By heating, or by doing work
What is the formula for kinetic energy?
- 5 x mass x speed squared
0. 5mv²
What does the energy in the kinetic energy store depend upon?
The object’s mass and speed
The greater an objects mass and faster it goes, what does this mean for its kinetic energy store?
There will be more energy in its kinetic energy store
When does energy get stored in gravitational potential energy stores?
When the object is raised
What is the formula for gravitational potential energy?
Mass x Gravitational field strength x height
mgh
kg x N/kg x m
What is the gravitational field strength on Earth?
10N/kg
Falling objects transfer energy. True or false?
True, when something falls, energy from its gravitational potential energy store is transferred to its kinetic energy store.
Energy lost from the g.p.e store = what?
Energy gained in the kinetic energy store
When does energy get transferred to the elastic potential energy stores?
When the object is stretched
Give the formula for elastic potential energy (J)
- 5 x spring constant (N/m) x extension² (m)²
0. 5ke²
What does specific heat capacity mean?
The amount of energy needed to heat 1kg of a substance by 1 degree C
What is the equation for specific heat capacity (J/kg degrees)?
mass (kg) x temperature change
Reorder this method for investigating different specific heat capacities
1) When you’ve collected enough readings (10 should do it), turn off the power supply. Using your measurement from the current and voltage from the power supply, you can multiply them to find the power that went into the heater. This calculates how much energy has been transferred to the heater at the time of each temperature reading using the formula E=Pt (t is seconds)
2) You can now repeat this with different materials, then compare
3) Measure the mass of the block, then wrap it in an insulating layer (e.g. a thick layer of newspaper) to reduce the energy transferred from the block to the surroundings. Insert the heater and thermometer
4) To investigate a solid material, you’ll need a block of the material with 2 holes in it (for the heater and the thermometer)
5) If you assume all the energy supplied to the heater has been transferred to the block, you can plot a graph of energy transferred to the thermal energy store of the block against temperature. It should look something like curved at the start, then shoots upwards.
6) When you turn on the power, the current in the circuit does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. This energy is then transferred electrically from the power supply to the heater’s thermal energy store by heating, causing the material’s temperature to increase
7) Find the gradient of the straight part of the graph. This is temperature change ÷ energy change. So, the specific heat capacity is 1 ÷ (gradient x mass of block).
8) Measure the initial temperature of the block, and set the initial voltage to be 10V. Turn it on and start a stop watch
9) As the block heats up, take readings of the temperature and current every minute for 10 mins. The current through the circuit shouldn’t change as the block heats up
4) To investigate a solid material, you’ll need a block of the material with 2 holes in it (for the heater and the thermometer)
3) Measure the mass of the block, then wrap it in an insulating layer (e.g. a thick layer of newspaper) to reduce the energy transferred from the block to the surroundings. Insert the heater and thermometer
8) Measure the initial temperature of the block, and set the initial voltage to be 10V. Turn it on and start a stop watch
6) When you turn on the power, the current in the circuit does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. This energy is then transferred electrically from the power supply to the heater’s thermal energy store by heating, causing the material’s temperature to increase
9) As the block heats up, take readings of the temperature and current every minute for 10 mins. The current through the circuit shouldn’t change as the block heats up
1) When you’ve collected enough readings (10 should do it), turn off the power supply. Using your measurement from the current and voltage from the power supply, you can multiply them to find the power that went into the heater. This calculates how much energy has been transferred to the heater at the time of each temperature reading using the formula E=Pt (t is seconds)
5) If you assume all the energy supplied to the heater has been transferred to the block, you can plot a graph of energy transferred to the thermal energy store of the block against temperature. It should look something like curved at the start, then shoots upwards.
7) Find the gradient of the straight part of the graph. This is temperature change ÷ energy change. So, the specific heat capacity is 1 ÷ (gradient x mass of block).
2) You can now repeat this with different materials, then compare
What is the conservation of energy principle?
“Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed”
When energy is transferred between stores, not all of the energy is transferred usefully into the stores you want it to go. Where does the energy go?
Some energy is dissipated when energy transfer takes place.
Normally as thermal energy
Describe the energy transfers for a closed system with soup and a spoon
A cold spoon is dropped into an insulated flask of hot soup, which is then sealed. You can assume the flask is a perfect thermal insulator so they form a closed system. Energy is transferred from the thermal energy store of the soup to the useless thermal energy store of the spoon (causing the soup to cool slightly, and the spoon to heat up). Energy transfers have occurred within the system, but no energy has left the system - so the net change is still 0
“The rate of doing work” or the rate of energy transfer/ doing work is what word?
Power (watts)
What does 1 watt equal?
1 joule of energy transferred per second
Give the equations to calculate power
Energy transferred ÷ Time
OR Work done ÷ Time
Always Joules ÷ seconds
What makes something powerful?
How much energy it can transfer in a short amount of time
What does lubrication do?
Reduces frictional forces - helps to reduce unwanted energy transfers
List 2 things that can help reduce energy transfers
Lubrication
Thermal insulation
What is the difference between conduction and convection?
Conduction is when the heated particles vibrate, collide with each other and transfer energy between their kinetic energy stores.
Convection is due to liquids and gases flowing, so the warmer and less dense region will rise above the denser, cooler regions. So, energy particles move away from hotter to cooler regions
What is thermal conductivity?
A measure of how quickly the energy is transferred through the heat making particles collide and kinetic energy stuff way
How does insulation help reduce unwanted energy transfers?
It reduces the rate of energy transfer by heating
How can you keep a house warm? (insulate it)
Have thick walls made of a low thermal conductivity
Using thermal insulation -
some with cavity walls (air gaps reduces amount of energy transferred by conduction as there’s a gap),
some with loft insulation to reduce convection (heat rising, cooling then sinking),
some double-glazed windows (working same as cavity walls),
some draught excluders around doors and windows to reduce convection
