Energy Flashcards
Define magnetic energy.
Energy stored when two attracting magnetic poles are pulled close together, repelling poles pushed further apart.
Define thermal energy.
Amount of energy in a substance.
Define chemical energy.
Energy stored in chemical bonds.
Define kinetic energy.
Energy possessed in an object due to its motion.
Define gravitational potential energy.
Energy possessed in an object due to its height in a gravitational field.
Define electrostatic energy.
Energy stored when attracting electrical charges move close together, repelling further apart.
Define elastic potential energy.
Energy stored in an object when is is stretched or compressed.
Define nuclear energy.
Energy stored in a nucleus of an atom.
Define a system.
An object/group of objects.
When energy is transferred, what is the effect on a system?
It changes.
Define work done mechanically?
Energy required to exert a force to move an object.
Define work done electrically?
Energy required to overcome the resistance of a circuit and allow current to flow.
Work done when a car collides with a stationary object?
Normal contact force of collision does work, transferring the car’s kinetic energy to the elastic potential and gravitational potential of the car and its body, as well as some being dissipated via sound waves.
Define gravity?
Force of attraction between two objects.
What two factors do the strength of gravity depend on?
-Mass of the two objects
-Distance between the two objects.
Define gravitational field.
Field of influence by a large object on nearby objects.
Define gravitational field strength?
Strength of gravitational field acting on an object.
Define weight?
Force acting on an object due to gravity.
Define mass?
Amount of matter in an object, an intrinsic quality.
9-stepped practical of calculating the specific heat capacity of a material.
-For a solid, obtain a block of it with two holes; one for a thermometer and one for a heater.
-Record mass of block, add layer of insulating material to reduce the energy transfer by conduction. Insert heater and thermometer.
-Measure initial temperature of the block, set p.d. of the power supply to 10V. Turn on the heater and stop the stopwatch.
-As power turns on, current does work on the heater, transferring energy from the electrical energy of the supply electrically to the thermal energy store of the heater, and via heating to the thermal energy store of the block, causing its temperature to increase.
-As the temperature of the block increases, record readings of the temperature and current
each minute for 10 minutes, expecting the current to remain constant.
-After 10 readings, turn off the power supply. Calculate power using P=VI and from this energy transferred using E=PT.
-Assume all energy supplied to the heater is transferred usefully, and plot on graph.
-Measure gradient of graph, change in temperature/change in energy, and using the equation change in temperature=mass
x specific heat capacity x change in energy, the specific heat capacity of the substance is 1/gradient of straight part x mass.
-Repeat for different materials and compare.
How can the reading of the thermometer be improved?
Add a few drops of water into the hole for the thermometer in the block before inserting it to improve thermal contact and ensure even heating.
First part of the graph is not straight?
Thermal inertia occurs at the start as the block and heater take time to heat up.
Safety precautions for practical?
-Avoid touching the metal when it is heated.
-Use a heatproof mat
-Avoid spilling water on the power supply when inserting it in the hole of the block.
Conservation of energy definition.
Energy can be usefully transferred/store/dissipated but not created or destroyed.
Open system and closed system difference in terms of energy?
-Open system can exchange matter and energy with the “outside environment”.
-A closed system is unable to do this, with net energy transfer always 0.
Definition of power.
Rate that energy is transferred/work is done.
So is something powerful able to always exert a large force?
No it simply is able to transfer large amounts of energy in a short amount of time.
Definition of conduction.
Process of energy transfer by vibrating particles to neighbouring particles.
Describe the process of conduction.
-Material is heated, energy transferred to thermal energy store of substance, shared between particles’ kinetic energy store, causes them to vibrate more, colliding with neighbouring particles, adding to their kinetic energy stores.
-This process continues until heat and energy transferred is spread evenly across the material. Energy then is transferred to the surroundings/neighbouring material.
Definition of thermal conductivity.
A measure of how quickly energy is transferred in a material.
Thermal conductivity in metals?
High
Thermal conductivity in plastics?
Low, and so are used as insulators.
Thermal conductivity in fluids?
Low.
In what states will convection occur in?
Fluids, i.e. liquids and gases.
Definition of convection
Process of energy transfer by which energetic particles with more energy move from hotter to cooler regions in the substance.
Describe the process of convection.
-Energy is transferred via heating to a liquid flowing, to their thermal energy store, shared between particles’ kinetic energy stores.
-As particles are able to move in fluids, when they are heated, they can move faster, with the space between the particles increasing, and so the density of that region therefore decreases.
-As the particles can flow, warmer and less dense regions rise above dense cooler regions. If a constant heat source is applied, a convection current is created.
Describe how radiators create convection currents?
-Energy is transferred from the radiator to nearby particles by conduction, as particles collide with the surface of the radiator.
-Air by the radiator therefore gets warmer, and so moves faster, becoming less dense.
-Warm air rises and is replaced by the cooler air, which then is heated and its density decreases, rising.
-At the same time, the hotter regions transfer energy to the surroundings, like the walls and contents of the room, becoming dense, and sinking again.
-This cycle repeats, and therefore causes a flow of air circulating around the room, a.k.a. a convection current.
Definition of radiation.
Process of energy transfer, without particles, through a vacuum, via infrared waves.
Hot objects will emit radiation?
Will emit more IR radiation than it absorbs.
Definition of a fluid.
A substance in which particles can move.
How does sealing a house decrease unwanted energy transfers?
Use of equipment like foam seals and curtains prevent air pass out and so decrease the rate of energy transfer by convection.
How do thick walls decrease unwanted energy transfers?
Decrease the thermal conductivity of the walls, and therefore the rate of energy transfer by conduction that it will do.
Name 4 types of insulation.
-Cavity wall insulation.
-Double glazing of windows.
-Loft insulation
-Draught excluders.
