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Flashcards in P1: Energy Deck (67)
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What are the types of energy store?

-Thermal -Kinetic -Gravitational -Elastic potential -Chemical -Magnetic -Electrostatic -Nuclear


What are the types of energy transfer?

-Mechanically (by a force doing work) -Electrically (work done by moving charges) -By heating -By radiation (through the EM spectrum, e.g. light or UV radiation) Overall, energy can be transferred by heating or by doing work.


What is a closed system?

Closed systems are ones where neither energy nor matter can leave. The net change in total energy is always zero.


What is the equation for kinetic energy?

Kinetic energy (J) = ½ x mass (kg) x velocity2 (m/s) Ek = ½ mv2


What is the equation for gravitational potential energy?

Gravitational potential energy (J) = mass (kg) x gravitational field strength (N/kg) x height (m) Ep = mgh


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 energy


What is power and what is it measured in?

Power is the rate of energy transfer / work done, measured in watts (W).


What are the two equations for power?

1) Power (W) = energy transferred (J) ÷ time (s) P = E/t 2) Power = work done (J) ÷ time (s) P = W/t


No device is 100% efficient, except for ____.

electric heaters


What are the two ways to calculate efficiency?

1) Efficiency = useful energy output ÷ total energy input 2) Efficiency = useful power output ÷ total power input


What causes energy to be wasted?

When something moves, there’s usually at least one frictional force acting against it, causing some energy in the system to be dissipated.


What are 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 liquids (e.g. oil)?

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 stores 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 (so in a gas/liquid), 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 will rise above cooler, denser regions. -So more energetic particles move from hotter to cooler regions: this is convection.


What are 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.


The formula for specific heat capacity is given (ΔE = mcΔθ). What is its symbol and unit?

Symbol: c

Unit: J / kg°C


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.


Specifically what are non-renewable energy resources?

They are nuclear fuel (uranium and plutonium) and fossil fuels (natural resources that form underground over millions of years, typically burnt to provide energy). The three main ones are coal, oil and natural gas.


Non-renewables provide most of our energy. Why?

They are reliable. There is enough fuel to meet current demand, and they are extracted at a fast enough rate that power plants always have fuel in stock, so they can respond quickly to changes in demand.


What are the pros of fossil fuels?

• Reliable.

• Enough to meet current demand and respond to changes in demand.

• Cost effective: while the setup costs of power plants are high, running and fuel extraction costs are fairly low.


What are the cons of fossil fuels? Give at least three.

• Finite/non-renewable.

• They release CO2 into the atmosphere when burned, adding to the greenhouse effect and global warming.

• Power plants ruin the view.

• Burning coal and oil releases sulfur dioxide, causing acid rain. Reduced by taking sulfur out before combustion.

• Coal mining, especially open cast, ruins the landscape.

• Oil spillages cause serious environmental problems.