Topic 1 - Energy Flashcards
What are the four ways energy can be transferred
mechanically, electrically, by heating or radiation
What is a system
A single object or group of objects that you are interested in
What happens when a system changes
Energy is transferred either
-Into or away from the system
-Between different objects in the system
-Or between different types of energy stores
What is a closed system
A system where neither matter or energy can enter or leave. The net change in the total energy of a closed system is always 0.
Give an example of energy stores transferring from a kettle to water when the object is water
Water is the store so as the kettle heats up the water using its heating element it transfers energy into the waters thermal store, causing the temperature of the water to rise
Give an example of energy stores transferring from a kettle to water when the kettle and water are a two object system
Energy is transferred electrically to the thermal energy store of the kettles heating element which transfers energy by heating to the waters thermal energy store
What is work done
Energy transferred
When can work be done?
-When current flows (work is done against resistance in a circuit)
-By a force moving an object
Outline the work done when throwing a ball upwards
It causes a transfer from the chemical energy store of the persons arm to the kinetic energy store of the ball and the arm
Outline the work done between a car brakes and wheels as the car slows down
The friction between the brakes and wheels causes an energy transfer from the wheels kinetic energy stores to the thermal energy store of the surroundings
How do falling objects transfer energy
When something is dropped from a height it’s accelerated by gravity and the gravitational force does work
As it falls energy from the objects gravitational potential energy is transferred to its kinetic energy store
What happens when there is a falling object and there’s no air resistance
Energy lost from the g.p.e store = energy gained in the kinetic energy store
What does air resistance cause to energy from the object falling to do
Causes some energy to be transferred to other energy stores (e.g. the thermal energy stores of the object and surroundings)
What affect does speed have on energy ?
Anything moving has energy in it’s kinetic energy store. Energy is transferred to this store when an object speeds up and is transferred away from this store when an object slows down
How does speed and mass affect the kinetic energy of a system
The greater it’s mass and the faster it’s going the more energy there will be in its kinetic energy store
What’s the formula for kinetic energy
Ek = 1/5mv ²
Kinetic energy (J) = 1/2 x mass (kg) x speed ² (m/s ²)
How does lifting an object affect its energy
Lifting an object in a gravitational field requires work, causing a transfer of energy to the gravitational potential energy store of the raised object. The higher the object is lifted, the more energy is transferred of this store
What properties of an object does the amount of energy in a g.p.e store depend on
-Height
-Mass
-Strength of the gravitational field the object is in
Equation for gravitational potential energy
Ep = m x g x h
Gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m)
What affects the elastic potential energy store of an object
Stretching or squashing it can transfer energy to the elastic potential energy store
What’s the equation for finding elastic potential energy
Ee = 1/2ke ²
Elastic potential energy (J) = 1/2 x spring constant (N/m) x extension ² (m)
What is a specific heat capacity
When more energy needs to be transferred to the thermal energy store of some materials to increase their temperature than others
How much energy do you need to warm 1kg of water by 1°C
4200J
How much energy do you need to warm 1kg of mercury by 1°C
139J
What is the measure of specific heat capacity
The amount of energy needed to raise the temperature of 1kg of a substance by 1°C
What’s the equation that links energy transferred to specific heat capacity
ΔE = mc Δ θ
Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg°C) x temperature change
Outline the practical to investigate specific heat capacity
-You’ll need a block of the material with two holes in it for the heater and thermometer to go into
-Measure the mass of the block and wrap it in an insulating layer (e.g. thick newspaper) to recuse the energy transferred from the block to the surroundings and insert the thermometer and heater
-Measure initial temperature and set the potential difference of the power supply to 10V and turn it on and start a stopwatch
-When you turn on the power it does work on the heater, transferring energy electrically from the power supply to the heaters thermal energy store. This energy is then transferred to the material’s thermal energy store by heating, causing the materials temperature to increase
-As the block heats use thermometer to measure it’s temperature at an even time interval and make sure the current doesn’t change
-When you have enough reading turn off the power supply
-Calculate to find the materials specific heat capacity
For the specific heat capacity experiment what calculations do you do to find the capacity
- Calculate the power supplied to the heater using Power = current x potential difference
- Then calculate how much energy has been transferred to the heater at the time of each temperature reading using the formula Energy = power x time
- Plot graph of energy transferred to thermal energy store against temperature
- Find the gradient of the straight part of the graph ( change in temp / change in thermal energy)
- The specific heat capacity is 1 / (gradient x mass of the block)
What is the conservation of energy principle
Energy can be transferred usefully, stored of dissipated but can never be created or destroyed
Why isn’t all energy transferred usefully into the store it should go into
Some energy is always dissipated when an energy transfer takes place
Why is dissipated energy sometimes called wasted energy
Because the energy is being stored in a way that isn’t useful
Mobile phones as source of dissipated energy
When using a mobile phone energy is usefully transferred from the chemical energy store of the battery in the phone. But some is dissipated in this transfer to the thermal store and you will feel you phone getting warmer if you use it for a long time.
Flask of soup and cold spoon as an example of an energy transfer in a closed system
Cold spoon is dropped into insulated flask of hot soup which is then sealed. Energy is transferred from the thermal energy store of the soup to the useless therm energy store of the spoon so the soup cools slightly. Energy transfers have occurred within the system but no energy has left the system - so the net change in energy is 0.
What is power
The rate of energy transfer or the rate of doing work
What is the equation that links power, energy transferred and time
Power = Energy transferred / time
P = E / t
What is the equation that links power, work done and time
Power = work done / time
What are the units for power
Watts (W)
What happens to the systems energy store when a collision between a car and stationary object takes place
The normal contact force between car and object does work. It causes energy to be transferred from the cars kinetic energy store to other energy stores (e.g. the elastic potential and thermal energy stores of the object and the car body) Some energy may be transferred away by sound waves
