Topic 1a - Energy Transfers Flashcards
Where is energy stored?
When energy is transferred to an object, the energy is stored in one of the object’s energy stores.
What are 8 energy stores?
- Kinetic
- Thermal
- Chemical
- Gravitational Potential
- Elastic Potential
- Electrostatic
- Magnetic
- Nuclear
What is a system?
A system is an object or group of objects.
What is a closed system?
A system where neither matter nor energy can enter or leave. The net change in the total energy of a closed system is always zero.
What happens when a system changes?
Energy is transferred. It can be transferred, into or away from a system, between different objects in the system, or between different energy stores.
What are the 3 main types of energy and what do they mean?
- Kinetic energy - energy of an object that is in motion.
- Potential energy - energy that has the potential to be converted into another form of energy. Eg, gravitational potential energy or elastic potential energy.
- Heat/Thermal energy - something that gives out heat or becomes hot, normally due to the presence of a frictional force.
What are 6 other examples of energy, that aren’t the main 3?
- Solar energy
- Nuclear energy
- Hydroelectric energy
- Chemical energy
- Tidal energy
- Wave energy
What is the law/principal of conservation of energy? (2)
- In a closed system, the total energy before a process is the same as the total energy after the process.
- Energy can never be created or destroyed, it can only be converted from one form to another, and stored/dissipated.
How does energy change when an object is projected upwards? (3)
- Before the ball is thrown upwards, the person holding the ball has energy in their chemical store.
- When the ball is thrown, some of that energy is transferred to the kinetic store of the ball as it begins to move upwards.
- As the height of the ball increases, energy from the kinetic store of the ball is transferred to its gravitational potential store.
How does energy change when a moving object hits an obstacle? (3)
- When an object, such as a car, is moving, energy in the chemical store of the fuel is transferred to the kinetic store of the car.
- If the object hits an obstacle, such as the car hitting a wall, the speed of the car will decrease very quickly.
- Therefore, the energy in its kinetic store will decrease.
Where does the energy transfer to when a moving object hits an obstacle? (3)
- In the scenario of a car hitting a wall, most of the energy from its kinetic store is transferred to the thermal store of the surroundings (dissipated).
- Energy is transferred mechanically to the thermal store of the wall (the force of the car on the wall).
- Energy is also transferred by heating to the thermal store of the car, the wall. and to the thermal store of the air as the sound waves transfer energy away from the system (causing the air particles to vibrate).
How does energy change when a vehicle is accelerated by a constant force? (2)
- When a vehicle is stationary, it has energy in the chemical store of the fuel.
- When the vehicle speeds up or accelerates, the energy is transferred to the kinetic store of the car.
How does energy change when a vehicle slows down? (4)
- When a vehicle is moving, it has energy in its kinetic store.
- As it slows down or decelerates, energy is transferred to the thermal store of the surroundings (dissipated).
- This energy is transferred by heating due to friction between the tyres on the ground, and due to friction between the brakes and the brake pads.
- Energy is also transferred by heating as the sound waves transfer energy away from the system (making the air particles vibrate).
How does energy change when water boils in a kettle? (2)
- When an electric kettle boils water, energy is transferred by electrical working from the mains to the thermal store of the heating element inside the kettle.
- As the heating element gets hotter, energy is transferred by heating to the thermal store of the water.
What is the transfer pathway of mechanical working?
When a force acts on an object (e.g. pulling, pushing, stretching, squashing).
What is the transfer pathway of electrical working?
A charge moving through a potential difference (e.g. current).
What is the transfer pathway of heating by particles?
Energy is transferred from a hotter object to a colder one (e.g. conduction).
What is the transfer pathway of heating by radiation?
Energy transferred by electromagnetic waves (e.g. visible light).
What do all objects in motion have?
Kinetic energy
What is the equation for kinetic energy?
- KE = 1/2 m v(2)
- KE - energy in joules, J
v - speed in m/s
m - mass in Kg
What does gravitational potential energy depend on?
How far up/down an object is relative to the ground or another surface. The further up an object is, the larger its gravitational potential energy.
What is the equation for gravitational potential energy?
- GPE = mgh
- m - mass in Kg
g - gravitational field strength in N/kg
h - height in metres, m
GPE - in joules, J
What is the gain in GPE equal to?
The work done in lifting.
What happens when objects are released from a height/when they lose height?
The GPE is converted into KE, provided there is no work done against friction.
Where is elastic potential energy/strain stored?
In a spring, or something of a similar nature.
What is the equation for elastic potential energy/strain?
- elastic PE = 1/2 k e(2)
OR - elastic PE = 1/2 F e (because F = ke)
- k - spring constant in N/m
e - extension of spring in m
elastic Pe - joules, J
What is the equation for power?
- Power = energy transferred / time taken
P = E/t - P - power in watts, W
E - energy transferred in joules, J
t - time in s
What is 1 watt equal to?
An energy transfer of 1 joule per second is equal to a power of 1 watt.
1W = 1J / 1s
What is another way to calculate power?
- P = work done / time taken
- P = Fd / t = F x (d/t) => avg speed
- P = Fv
When the speed and force are constant/average. - P - power in W
F - force in N
v - avg speed in m/s
What can power also be defined as?
The rate of transfer of energy.
What is efficiency?
The amount of useful energy in relation to the input energy.
OR
The ratio between the useful power and the input power.
How is efficiency calculated - energy terms?
efficiency = (useful energy out / total energy in) x 100
How is efficiency calculated - power terms?
efficiency = (useful power out / total power in) x 100
What is efficiency given as?
A percentage.
What is the equation for change in energy?
ΔE = mcΔθ
Where:
ΔE = change in energy, in joules (J)
m = mass, in kilograms (kg)
c = specific heat capacity, in joules per kilogram per degree Celsius (J/kg °C)
Δθ = change in temperature, in degrees Celsius (°C)
What is the specific heat capacity of a substance defined as?
The amount of energy required to raise the temperature of 1 kg of a substance by 1 °C .
What does a low specific heat capacity mean?
If a substance has a low specific heat capacity, it heats up and cools down quickly. It takes less energy to change its temperature.
What does a high specific heat capacity mean?
If a substance has a high specific heat capacity, it heats up and cools down slowly. It takes more energy to change its temperature.
What is the 16 step method for the required practical of investigating specific heat capacity?
- Measure and record the mass of the copper block in kg.
- Wrap the block with some insulating material and place it in a calorimeter (container). Place the whole calorimeter and block on a heat mat.
- Place a heater in the larger hole in the block.
- Connect the ammeter, power pack and heater in series (see diagram). Connect the voltmeter across the power pack. Set the power pack to 12 V.
- Use the pipette to put a small amount of water in the other hole.
Put the thermometer in this hole. - Switch on the power pack briefly to record the ammeter and voltmeter readings. These should stay the same during the experiment. Switch it off again.
- Calculate the power of the heater in watts. To do this, multiply the ammeter reading by the voltmeter reading. Record this calculation and the value of the power in your lab book.
- Create a table with three columns - time (seconds, work done and temperature. You will record the temperature every minute for 10-15 minutes.
- Record the initial temperature of the block.
- Switch on the power pack and start the stop clock at the same time.
- Calculate the energy transferred by the heater after every minute. To do this, multiply the time in seconds by the power of the heater.
E = (power) x (total time) => where total time is the time since the start of the experiment - Plot a graph of temperature in oC in the x-axis and energy transferred in J in the y-axis.
- Draw a line of best fit. Take care as the beginning of the graph may be curved.
- Calculate the gradient of the straight part of your graph and its unit.
- The heat capacity of the block is the amount of energy needed to raise the temperature of the block by 1°C and it is the gradient of the graph.
𝑔𝑟𝑎𝑑𝑖𝑒𝑛𝑡= 𝛥𝐸 / 𝛥𝜃 - The specific heat capacity is the heat capacity divided by the mass of the block in kg. Calculate the specific heat capacity of the material of the block.
What is the independent variable for the required practical of investigating specific heat capacity?
Time, t
What is the dependent variable for the required practical of investigating specific heat capacity?
Temperature, θ
What are the control variables for the required practical of investigating specific heat capacity? (3)
- Material of the block
- Current supplied, I
- Potential difference supplied, V
How do energy transfers by heating work?
Energy transfers by heating increase the energy in the kinetic store of the particles that make up that system, which increases the energy in the thermal store of the object. This either raises the system’s temperature or, produces a change of state (eg. solid to liquid).
What is an example of an energy transfer by heating?
An example of an energy transfer by heating is warming a pan on a hob. Energy is transferred electrically from the mains supply to the thermal store of the hob which is then transferred by heating to the thermal store of the pan.
How is energy transferred when a person pushes a box along the floor? (2)
- If the system is defined as the man and the box, energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box.
- If the system is defined as the box and the floor, energy is transferred by heating from the kinetic store of the box to the thermal store of the floor (due to friction) and by heating to the thermal store of the surroundings as the sound waves transfer energy away from the system and cause the air particles to vibrate.
What is current?
Current is the flow of charge. A current flows when there is a potential difference applied to the circuit. This is provided by the power supply or a cell.
How is energy transferred in a circuit containing a cell, wires and a lamp? (3)
- Energy from the chemical store of the cell is transferred electrically to the thermal store of the lamp as the filament heats up.
- Energy is transferred from the thermal store of the lamp by heating and by radiation (light) to the thermal store of the surroundings.
- Energy is also transferred by heating to the thermal store of the wires (due to resistance).
