PHYSICS P1 Flashcards
(32 cards)
What is the law of conservation of energy?
Energy cannot be created or destroyed, only transferred stored or dissipated.
Total energy in = total energy out
Total energy in = Useful energy out + Wasted energy
What are the 5 main energy stores?
Changes in a system
Chemical - The energy stored in chemical bonds, such as those between molecules.
Kinetic - The energy of a moving object.
Thermal - Total kinetic and potential energy of the particles in an object, in most cases this is the vibrations.
Gravitational PE - The energy of an object at height.
Elastic PE - The energy stored when an object is stretched or squashed.
What are the four types of energy transfer?
example question - How is energy transferred here?
Mechanical work - a force moving an object through a distance
Electrical work - charges moving due to a
potential difference
Heating - due to temperature difference caused electrically or by chemical reaction
Radiation - energy transferred as a wave,
What are some examples of energy being dissipated?
- For a radio or set of speakers, the
electrical work is transferred into useful sound waves and infrared radiation is dissipated - ie wasted as heat energy - For a tumble dryer, the electrical work is transferred into useful thermal energy which helps to dry clothes - energy is dissipated by sound waves
Remember to google the equations sheet on google and learn the different symbols for each equation.
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When work is being done, what happens to the energy?
It’s being transferred from one store to another, the amount of energy transferred is the amount of work being done.
What two things does the amount of work done when a force acts on a body depend on?
- The size of the force acting on an object
- The distance through which the forces causes the body to move in the direction of the force
Practice calculations for p1.
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What is 1 watt equal to in terms of energy?
It’s equal to one joule per second, for every extra joule transferred per second, the power increases by 1 watt.
e.g. A hair dryer transfers 48,000 J of energy in one minute. The power rating is 800w because 48,000 divided by 60 is 800.
What is meant by power?
The amount of energy that is transferred per second.
What is meant by the efficiency of a device?
The proportion of the energy supplied that is transferred in useful ways.
What are the useful and wasted stores of energy for a washing machine?
Useful stores - kinetic energy of the drum, internal (thermal) energy of the water.
Wasted stores - sound radiation and infrared radiation dissipated to the surroundings.
What is the three ways that energy is transmitted?
Convection, Conduction or Radiation.
What is a conductor?
A material that allows internal (thermal) energy to be transmitted through it easily.
Describe what happens when metal is put on a fire?
The energy from the flame makes the
ions in the metal vibrate faster. Since the ions in the solid metal are close together, this increased
vibration means that they collide with neighboring ions more frequently. Energy is passed on through the metal by these collisions, transmitting the energy. More frequent collisions increase the rate of transfer.
What is meant by an insulator?
A material that will not allow the easy flow of energy.
How can the conductivity of metals be compared?
By examining the time taken to transmit energy through them. Three rods can be placed at one end with the same flame and whichever rod gets the hottest at the other end is the best conductor.
What is thermal conductivity?
A measure of how well a material conducts energy when it is heated.
Why is it better to have a window made of two layers of glass with a layer of air trapped between them?
Both glass and air are insulators because they have low thermal conductivities. The layer of air has the lowest thermal conductivity and reduces the overall conductivity of the window unit.
What is the practical for investigating the effectiveness of insulating materials?
- Place a small beaker into a larger beaker.
- Fill the small beaker with hot water from a kettle.
- Put a piece of cardboard over the beakers as a lid. The lid should have a hole suitable for a thermometer.
- Place a thermometer into the smaller beaker through the hole.
- Record the temperature of the water in the small beaker and start the stopwatch.
- Record the temperature of the water every 2 minutes for 20 minutes.
- Repeat steps 1-6, each time packing the space between the large beaker and small beaker with the chosen insulating material.
- Plot a graph of temperature (y-axis) against time (x-axis).
What is meant by specific heat capacity?
The energy required to raise one kilogram (kg) of the material by one degree Celsius (°C).
Different materials require different amounts of energy to change temperature. What does the amount of energy needed depend on?
- The mass of the material
- The specific heat capacity of the material
- The desired temperature change
What is the practical for specific heat capacity?
- Place the immersion heater into the central hole at the top of the block.
- Place the thermometer into the smaller hole and put a couple of drops of oil into the hole to make sure the thermometer is surrounded by hot material.
- Fully insulate the block by wrapping it loosely with cotton wool.
- Record the temperature of the block.
- Connect the heater to the power supply and turn it off after ten minutes.
- After ten minutes the temperature will still rise even though the heater has been turned off and then it will begin to cool. Record the highest temperature that it reaches and calculate the temperature rise during the experiment.
What are some examples for why energy is needed?
- Cooking
- Heating
- Public services
- Factories
- Transport
