Topic 1 Flashcards
(16 cards)
What are 8 energy stores? (4 marks)
Thermal, kinetic, gravitional potential, elasatic potential, chemical magnetic, electrostatic, nuclear
How is energy transferred? (3 marks)
Energy is transferred mechanically (force doing work), electrically (work done by moving charges), heating or radiation (heat or sound)
How is energy transferred and what can it be transferred by? (6 marks)
When a system changes energy is transferred either into or away from the system, and either between different objects or different energy stores
It can be transferred by heating (e.g. boiling a kettle, water is the system and the energy is transferred to the water’s thermal energy store so its temperature rises)
It can also be transferred by doing work
What are three examples of work done. Explain how they are examples (4 marks)
Inital force exerted by a person to throw a ball upwards does work. It causes an energy transfer from the chemical energy store of the person’s arm to the kinetic energy store of the ball and arm
A ball dropped from a height is accelerate by gravity. The gravitational force does work. It causes energy to by transferred from the ball/s gravitational potential energy to the store to its kentic energy
Friction between a car’s brakes and its wheels does work as it slows down. It causes an energy transfer from the wheels’ kinetic energy stores to the thermal energy store of the surroundings
Describe the energy transfers tha occur when the wind causes a windmill to spin (3 marks)
Energy transfers mechanically from the wind’s kinetic energy store to the windmill’s kinetic energy store
Fill in the blanks:
Anything that is _____ has energy in its _____ energy store. Energy is transferred to this store with an objects _____ and is transferred _____ from this store when an objects _____ (6 marks)
Moving, kinetic, speeds up, away, slows down,
What is the forumla for kinetic energy? (2 marks)
Ek = ½mv2
Kinetic energy (J) = ½ x Mass (kg) x (speed)2
What causes more energy to be required when an object is lifted? Explain why. What formula could you use to figure this out? (3 marks)
There is a transfer of energy to the gravitational potential of the object in question. The higher the object is lifted, the more energy is requires
Ep = mgh
What happens to the gravitational potential energy store to a falling object with no air resistance? (2 marks)
When an object falls, all the energy from the gravitational potential energy store is transferred to its kinetic energy store without any waste
What is the formula for elastic potential energy stores? (1 mark)
Ee = ½ke2
Elastic potential energy (J) = ½ x Spring Constant (N/m) x extention
A 2.0 kg object is dropped from a height of 10m. Calculate the speed of theobject after it has fallen 5.0m, assuming there is no air resistance. Give your answer to 2 significant figures.
g = 9.8N/kg (5 marks)
The change in height is 5.0m. So the energy transferred from the gravitational potential energy store is:
Ep = mgh = 2.0 x 9.8 x 5.0 = 98J
This is transferred to the kinetic energy store of the object, so Ek = ½mv2 meaning:
v2 = 2Ek ÷ m = (2 x 98) ÷ 2.0 = 90m2/s2
v = √98 = 9.899 = 9.9m/s
Fill in the blanks:
More ______ needs to be ______ to the ______ store of some materials to ______ their temperature than others. Materials that need to ______ lots of energy in their thermal energ stores to ______ also transfer loads of energy when they ______ again
Energy, transferred, thermal energy, increase, gain, warm up, cool down
What is specific heat capacity? (2 marks)
The amount of energy needed to raise the temperature of 1kg of a substance to 1ºC
What the equation that links energy transferred to specific heat capacity? (1 mark)
ΔE = mcΔ
Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kgºC) x temperature change (ºC)
How do you investigate specific heat capacities? (9 marks)
- Get to a block of the material you’re investigating with two holes in it
- Measure the mass of the block, when 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 thermometer and heater as shown on the right
- Measure the initial temperature of the block and set the potential difference, V, of ther power supply to be 10V. Turn on the power supply and start a stop watch
- When you turn on the power, the current in the circuit (i.e. the moving charges) does work on the heater, transferring energy electrically from the power supply to the heater’s thermal energy store. This energy is then transferred to the material’s thermal energy store by heating, causing the material’s temperature to increase
- As the block heats up, take the reading of the temperature and current, I, every minute for 10 minutes. You should find that the current through the circuit doesn’t change as the block heats up
- Turn off the power supply after collecting around 10 readings, and using your measurement of the current, and the potential different of the power supply, you can use P = VI to calculate the power supplied to the heater. use E = Pt to calculate how much energy has been transferred to the heater at the time of each temperature reading.
- Assuming 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 the temperature. It should be curved at the beginning, forming into a stead line upwards
- Find the gradient of the straight part of the graph, this is ΔØ ÷ ΔE. Also using ΔE = mcΔ, figure out that the specific heat capacity of the material of the block is 1 ÷ (gradient x the mass of the block)
- Repeat this experiment with different materials to see how their specific heat capacities compare
Find the final temperature of 5kg of water, at an initial temperature of 5ºC, after 50kJ of energy has been transferred to it. The specific heat capacity of water is 4200J/kgºC (3 marks)
50,000 ÷ (5 x 4200) = 2.4
5 + 2.4 = 7.4
