P1 - Energy Flashcards
What the types of energy stores?
Thermal, kinetic, gravitational potential, elastic potential, chemical, magnetic, electrostatic and nuclear.
What are types of ways energy can be transferred?
Mechanically (by a force doing work), electrically (work done by electric charges), by heating, by radiation (through the EM spectrum).
What is a closed system?
A system in which neither energy nor matter can leave. The net change in total in always zero. E.g thermal flask of tea.
What is the equation for kinetic energy?
K.E. = 1/2mv²
What is the equation for gravitational potential energy?
EP=mgh
What is the equation for elastic potential energy?
EE = 1/2ke²
What is the law of conservation of energy?
Energy can be transferred usefully, stored or dissipated, but can never be created or destroyed.
Dissipated energy is often referred to as __ energy. This is usually transferred to a useless __ store.
1) wasted
2) thermal
What is power?
Power is the rate at which energy is transferred (or work done). It is measured in watts (W).
What is the equation for power?
P=e/t
No device is 100% efficient, except for __.
Electric heaters.
What is the equation for efficiency?
Efficiency = total useful energy output / total energy input
What causes energy to wasted?
When an object is moving, there is usually at least one frictional force acting against it, causing some energy in the system to be dissipated.
What are the three ways to reduce unwanted energy transfers?
1) Lubrication
2) Streamlining
3) Thermal insulation
How can lubrication reduce unwanted energy transfers?
Lubrication reduces frictional forces between surfaces of objects that are being rubbed together.
Why are lubricants usually liquid?
So that they coat objects and flow easily.
How can streamlining reduce unwanted energy transfers?
Streamlining reduces air resistance. Air resistance transfers energy from an object’s kinetic to thermal energy store.
In what two ways can heating occur?
1) Conduction
2) Convection
How does heating occur by conduction?
When an object is heated, energy is transferred to the kinetic energy store of its particles. This causes them to vibrate more and therefore collide more with each other. During these collisions, energy is transferred between the particles kinetic energy stores: This is conduction.
How does heating occur by convection?
If particles are free to move (liquid or gas), an increase in temperature means that energy is transferred to the kinetic energy stores of its particles. Particles move faster, so spacing between particles therefore increases. This causes the density of a heated region to decrease. The warmer, less dense region rises above the cooler, more denser regions. So more energetic particles move from hotter to cooler regions: This is called convection.
What are the three examples of thermal insulation? (Conduction)
-Having thick walls made from a material with low thermal conductivity. -Cavity walls: an inner and outer wall with an air gap in the middle. The gap reduces the amount of energy transferred by conduction through the walls. -Double glazing works in the same way: the air gap between two sheets of glass prevents energy transfer by conduction through the windows.
What are three examples of thermal insulation? (convection)
-Cavity wall insulation is where the gap between walls is filled with foam, which reduces energy transfer by convection in the wall cavity. -Loft insulation can reduce convection currents (a cycle where air particles are constantly heated, so rise, then cool and sink back down) being created in lofts. -Draught excluders around doors and windows reduce energy transfers by convection.
What is specific heat capacity?
The amount of energy required to raise the temperature of 1 kg of a substance by 1ºC.
What is the equation for specific heat capacity?
ΔE = mcΔθ
Describe how you would find the specific heat capacity of a solid block of a material.
You’ll need a solid block of the material, with 2 holes for the heater and thermometer to go into.
- Measure the block’s mass using a balance.
- Wrap it in an insulating layer (decreases energy dissipated from block to surroundings).
- Connect a heater to a power supply and ammeter, and place it into one of the object’s holes.
- Place a thermometer into the other and measure the initial temperature of the block.
- Set the power supply at 10V, then turn it on and immediately start a stopwatch.
- The current transfers energy to the heater’s thermal energy store, which is then transferred to the object’s.
- The ammeter reading should remain constant.
- Measure the temperature on the thermometer every 30 seconds. Turn off the power when you have 10 readings.
- Find the energy transferred to the heater at each reading using the formula E = VIt (bc E = Pt and P = VI).
- Assuming all the energy transferred to the heater was transferred to the block, find the SHC using the rearrangement c = ΔE/mΔθ.
- The plotted relationship between energy transferred and temperature would be directly proportional.
Describe how you could investigate the effectiveness of different insulators.
- Boil water in a kettle and use a balance to pour a set mass into a beaker.
- Use a thermometer to measure the initial temperature.
- Seal the beaker with a lid and use a stopwatch to leave it for 5 minutes.
- Remove the lid and measure the water’s final temperature.
- Pour away the water; allow the beaker to cool to room temperature.
- Repeat steps 1-4 (use same mass of water each time!), wrapping the beaker in a different material (foil, newspaper, bubble wrap) each time.
- The most effective insulator is that which reduces the temperature difference by the largest degree.
This investigation could be modified to instead test how the thickness of an insulator affects heat loss.
What are non-renewable energy resources?
Non-renewable energy resources are ones that cannot be replenished as they are used up. They usually do damage to the environment.
