energy Flashcards
What is the definition of a system in physics?
An object or group of objects that is defined to narrow the parameters to focus on relevant observations.
What happens to a system in equilibrium?
Nothing changes, and so nothing happens.
What occurs when there is a change to a system?
Energy is transferred.
What is stored in the kinetic energy store?
Moving objects have energy in their kinetic store.
How is energy gained in the gravitational potential store?
Objects gain energy when lifted through a gravitational field.
What is the elastic potential energy store?
Objects have energy in their elastic potential store if they are stretched, squashed, or bent.
What type of energy is found in magnetic materials?
Energy in their magnetic store.
What does the electrostatic energy store contain?
Energy from charged objects interacting with one another.
What happens during chemical reactions in terms of energy?
Energy is transferred into or away from a substance’s chemical store.
What is released from atomic nuclei during nuclear reactions?
Energy from their nuclear store.
What is the thermal energy store?
All objects have energy in their thermal store; the hotter the object, the more energy it has.
What are the pathways for energy transfer?
- Mechanical
- Electrical
- Heating
- Radiation
What is an example of energy transfer by heating?
A cup of hot coffee heating up cold hands.
What is the principle of conservation of energy?
Energy cannot be created or destroyed; it can only be transferred from one store to another.
What does the total energy in a closed system equal?
The total energy transferred into the system must equal the total energy transferred out.
What is wasted energy?
Energy dissipated to the surroundings that is not useful.
What is efficiency in an energy transfer?
A measure of the amount of wasted energy in an energy transfer.
How is efficiency calculated?
Efficiency = (useful energy output / total energy output) × 100%
What do Sankey diagrams represent?
Visual representations of energy transfers with arrows showing proportions of energy transfers.
What characterizes a good conductor?
A material that transfers energy by heating effectively.
What is an insulator?
A material that does not transfer energy by heating.
What happens during conduction in solids?
Atoms vibrate and bump into each other, transferring energy from atom to atom.
What is the main method of energy transfer by heating in solids?
Conduction.
What occurs when a fluid is heated?
The fluid expands, becomes less dense, rises, and cooler fluid moves in to take its place.
What is a convection current?
The motion resulting from the heating of a fluid.
What type of radiation do all bodies emit?
Infrared radiation.
Fill in the blank: The _______ of a system is defined as the ratio of the useful energy output to the total energy output.
[efficiency]
What happens to hot fluid in a convection current?
The hot fluid rises, and the cooler surrounding fluid moves in to take its place.
What occurs when hot fluid cools in a convection current?
The hot fluid cools, contracts and sinks back down again.
What is the resulting motion called when fluid moves due to temperature differences?
Convection current.
What type of energy transfer occurs in liquids and gases that aren’t trapped?
Convection currents will probably form.
What type of radiation do all bodies emit regardless of temperature?
Infrared radiation.
What is the relationship between an object’s temperature and the amount of infrared radiation it emits?
The hotter an object, the more infrared radiation it radiates in a given time.
Which type of objects are the best at emitting and absorbing thermal radiation?
Black objects.
Which type of objects are the worst at emitting and absorbing thermal radiation?
Shiny objects.
Fill in the blank: Black objects are good _______ and good _______.
[absorber], [emitter]
Fill in the blank: Shiny objects are very poor _______ and very poor _______.
[absorber], [emitter]
What is the primary method of energy transfer from the surface of a mug of hot coffee to the surroundings?
Radiation.
What process allows the most energetic particles of coffee to evaporate and set up a convection current?
Heating.
What happens to objects as they lose heat until they reach thermal equilibrium?
They reach equal temperature with their surroundings.
What is the aim of the experiment investigating conduction?
To investigate the rate of conduction in four different metals.
What is the independent variable in the conduction experiment?
Type of metal.
What is the dependent variable in the conduction experiment?
Rate of conduction.
What is the purpose of using a Bunsen burner in the conduction experiment?
To heat substances.
What materials are used in the conduction experiment?
Iron, copper, brass and aluminium.
What is the expected order of metals according to their thermal conductivity from highest to lowest?
- Copper
- Aluminium
- Brass
- Iron
convection experiment method
Fill the beaker with cold water (not too full) and place it on top of a tripod and heatproof mat
Pick up the crystal using forceps and drop it into the centre of the beaker – do this carefully to ensure the crystal does not dissolve prematurely
Heat the beaker using the Bunsen burner and record observations
Repeat experiment with hot water and record observations
What is the aim of the convection experiment?
To investigate the rate of convection of potassium permanganate crystals in two different temperatures of water.
What happens to the water when it is heated in the convection experiment?
It becomes less dense and rises.
What occurs when the water at the top of the beaker cools?
It becomes denser and falls downwards.
What is the aim of the radiation experiment?
To investigate how the amount of infrared radiation absorbed or radiated by a surface depends on the nature of that surface.
What is the independent variable in the radiation experiment?
Colour.
What is the dependent variable in the radiation experiment?
Temperature.
What is the main form of energy lost from the beakers during the radiation experiment?
Heating due to conduction and convection.
What is the significance of the thermal conductivity of a material in reducing energy loss?
Lower thermal conductivity means less energy is transferred.
What is cavity wall insulation designed to reduce?
Energy transfer by conduction and convection.
What is the primary method to reduce energy transfers by conduction?
Use materials with low thermal conductivity.
Fill in the blank: The insulator contains trapped air, which is a poor _______ conductor.
[thermal]
What happens to the rate of energy transfer from an object when it is properly insulated?
It stays warmer for longer.
True or False: Heat rises.
False.
What is the common mistake when explaining how insulators keep something warm?
Stating that the object warms up the insulator which then warms the object up.
What is work done?
Work is done when an object is moved over a distance by a force applied in the direction of its displacement
When is no work done on an object?
If a force is applied to an object but doesn’t result in any movement, no work is done
What is the relationship between work done and energy transfer?
The amount of energy transferred (in joules) is equal to the work done (also in joules)
What happens when a force acts in the direction of an object’s movement?
The object will gain energy, usually to its kinetic energy store
What happens when a force acts in the opposite direction to an object’s movement?
The object will lose energy, dissipated to the surroundings, usually by heating
How is work done on a ball when it is lifted?
Energy is transferred mechanically from the ball’s kinetic energy store to its gravitational potential energy store
What is the formula to calculate work done?
W = f × d
In the work done formula W = f × d, what does each symbol represent?
W = work done in joules (J), F = force in newtons (N), d = distance in metres (m)
What is gravitational potential energy?
The energy an object has due to its height in a gravitational field
What is the equation for calculating gravitational potential energy?
GPE = m × g × h
What do the symbols in the gravitational potential energy equation GPE = m × g × h represent?
GPE = gravitational potential energy in joules (J), m = mass in kilograms (kg), g = gravitational field strength in newtons per kilogram (N/kg), h = height in metres (m)
What is the approximate gravitational field strength on Earth?
Approximately 10 N/kg
What is kinetic energy?
The amount of energy an object has as a result of its mass and speed
What is the equation for calculating kinetic energy?
KE = 1/2 × m × v²
In the kinetic energy equation KE = 1/2 × m × v², what do the symbols represent?
KE = kinetic energy in joules (J), m = mass of the object in kilograms (kg), v = speed of the object in metres per second (m/s)
What does the conservation of energy principle state regarding work, GPE, and KE?
Whenever mechanical work is done, energy is transferred mechanically, and the amount of energy transferred is equal to the work done
What is power?
Power is work done per unit time
How can power also be defined in relation to energy?
Power is also energy transferred per unit time
What is the formula for calculating power?
P = W/t
In the power formula P = W/t, what do the symbols represent?
P = power measured in watts (W), W = work done in joules (J), t = time measured in seconds (s)
W
100 W
What is the power rating of a large power station?
10,000 MW
Fill in the blank: The gravitational potential energy equation is GPE = m × g × ____
h
how is a convection current formed? (5)
- water near heater is heated;
MP2. (heated) water expands;
MP3. density of (heated) water decreases;
MP4. lower density / warm water rises;
MP5. cooler / denser water sinks;
MP6. process repeats / is continuous
REJECT PARTICLES EXPAND
experiment conduction method
Attach ball bearings to the ends of each metal strip at an equal distance from the centre, using a small amount of wax
The strips should then be turned upside down and the centre heated gently using a bunsen burner so that each of the strips is heated at the central point where they meet
When the heat is conducted along to the ball bearing, the wax will melt and the ball bearing will drop
Time how long this takes for each of the strips and record in a table
Repeat the experiment and calculate an average of each time
experiment radiation method
Set up the four identical flasks painted in different colours: black, grey, white and silver
Fill the flasks with hot water, ensuring the measurements start from the same initial temperature
Note the starting temperature, then measure the temperatures at regular intervals, e.g. every 30 seconds for 10 minute
