Define closed system .

A system that can exchange energy but not matter with its surroundings.

Define conservation of energy .

Energy cannot be created or destroyed, it can only be transferred from one store to another.

State the four energy transfer pathways.

Mechanical working , electrical working , heating and radiation .

On a Sankey diagram, the width of each arrow is ______ to the amount of energy being transferred.

On a Sankey diagram, the width of each arrow is proportional to the amount of energy being transferred.

True or False? In an isolated system, energy can be transferred to the surroundings but matter cannot.

False. An isolated system allows the transfer of neither matter nor energy to or from its surroundings.

Define mechanical work .

Work that is done when a force acts over a distance.

State the four ways energy can be transferred within a system.

By heating (particles), by radiation , by mechanical work done by forces and by electrical work done when a current flows.

When a person pushes a box across the floor, describe the energy transfer between the person and the box.

Energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box.

Describe the energy transfer that takes place electrically as a filament lamp lights up.

Energy is transferred electrically from the chemical store of the cell to the thermal store of the filament wire, which then transfers energy by heating and by radiation as light.

Energy transferred by heating raises the ______ of a system or produces a change of state.

Energy transferred by heating raises the temperature of a system or produces a change of state.

True or False? Defining the boundaries of a system has no effect on which energy transfers need to be considered.

False. Defining the system gives a starting point and a stopping point for the energy transfers that need to be considered.

Work is done when an object is moved over a distance by a force applied in the direction of its displacement.

Describe the energy transfer that occurs when a bird flies through the air.

Energy is transferred from the bird's kinetic store to its thermal store, and dissipated to the thermal store of the surroundings due to air resistance.

Changes in ______ are related to gravitational potential energy, while changes in speed are related to kinetic energy.

Changes in height are related to gravitational potential energy, while changes in speed are related to kinetic energy.

True or False? Work done and energy transferred are the same physical quantity.

True. Work done = energy transferred .

Define gravitational potential energy .

The energy an object has due to its height in a gravitational field.

Define kinetic energy .

The amount of energy an object has as a result of its mass and speed .

In a ______ energy transfer, all of the gravitational potential energy is transferred to kinetic energy.

In a perfect energy transfer, all of the gravitational potential energy is transferred to kinetic energy.

True or False? A swinging pendulum is a good example of a perfect energy transfer between its kinetic and gravitational potential stores.

True. Energy is transferred back and forth between the kinetic and gravitational potential stores as the pendulum swings.

Define dissipated energy .

Energy that is spread out to the thermal store of the surroundings, usually as wasted energy.

Give three causes of unwanted heating in a system.

Air resistance , frictional forces and resistance in wires.

Explain why friction on a bicycle's gears and chain causes a wasted energy transfer.

Energy is transferred from the kinetic store of the bike to the thermal store of the gears and chain, so the rider must do more work to keep the bike moving.

How can friction between moving parts be reduced?

By lubricating the parts that rub together.

List two factors that affect the effectiveness of an insulator.

Its thermal conductivity and its thickness .

______ wall insulation reduces conduction of heat through the walls of a house from the inside to the outside.

Cavity wall insulation reduces conduction of heat through the walls of a house from the inside to the outside.

True or False? A denser insulating material is generally a better insulator.

False. The more dense the insulator, the more conduction can occur, so a less dense material insulates better.

The rate of energy transfer, or the rate at which work is done.

Two cars accelerate to the same final speed, doing the same amount of work. What does it mean if one car has more power?

It transfers that energy, or does that work, in a shorter amount of time.

1 joule of energy transferred per second ( 1 W = 1 J/s ).

1 kilowatt is equal to ______ watts.

1 kilowatt is equal to 1000 watts.

True or False? Power can be described as work done per unit time.

True. Since work done = energy transferred, power is also work done per unit time .

The ratio of the useful energy output from a system to its total energy output.

What is the difference between a system with high efficiency and one with low efficiency?

A high efficiency system transfers most of its energy usefully , with little wasted. A low efficiency system wastes most of its energy, with only a small amount useful.

Efficiency can be represented as a ______ or as a ______ .

Efficiency can be represented as a decimal or as a percentage .

True or False? Efficiency can be expressed in either joules or watts.

False. Efficiency has no units - it is expressed only as a ratio (decimal) or a percentage.

How do you convert an efficiency ratio into a percentage?

Multiply the ratio by 100 . For example, a ratio of 0.25 gives a percentage efficiency of 0.25 × 100 = 25% .

GCSEPhysicsEdexcelFlashcards8. Energy – Forces Doing WorkWork, Power & Efficiency

Work, Power & Efficiency (Edexcel GCSE Physics): Flashcards

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Define closed system.

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Cards in this collection (48)

Define closed system.
A system that can exchange energy but not matter with its surroundings.
Define conservation of energy.
Energy cannot be created or destroyed, it can only be transferred from one store to another.
Which energy store does a stretched elastic band have energy in?
The elastic potential store.
State the four energy transfer pathways.
Mechanical working, electrical working, heating and radiation.
A Sankey diagram shows a total energy input of 500 J, with 120 J transferred usefully. Calculate the wasted energy.
Wasted energy = total energy in − useful energy out
$500 - 120 = 380 J$
On a Sankey diagram, the width of each arrow is ______ to the amount of energy being transferred.
On a Sankey diagram, the width of each arrow is proportional to the amount of energy being transferred.
True or False?
In an isolated system, energy can be transferred to the surroundings but matter cannot.
False.
An isolated system allows the transfer of neither matter nor energy to or from its surroundings.
Define mechanical work.
Work that is done when a force acts over a distance.
State the four ways energy can be transferred within a system.
By heating (particles), by radiation, by mechanical work done by forces and by electrical work done when a current flows.
When a person pushes a box across the floor, describe the energy transfer between the person and the box.
Energy is transferred mechanically from the kinetic store of the person to the kinetic store of the box.
Describe the energy transfer that takes place electrically as a filament lamp lights up.
Energy is transferred electrically from the chemical store of the cell to the thermal store of the filament wire, which then transfers energy by heating and by radiation as light.
Energy transferred by heating raises the ______ of a system or produces a change of state.
Energy transferred by heating raises the temperature of a system or produces a change of state.
True or False?
Defining the boundaries of a system has no effect on which energy transfers need to be considered.
False.
Defining the system gives a starting point and a stopping point for the energy transfers that need to be considered.
Define work done.
Work is done when an object is moved over a distance by a force applied in the direction of its displacement.
If a force is applied to an object but the object does not move, how much work is done?
No work is done.
State the equation for calculating work done.
$E = F \times d$
E = work done in joules (J), F = force in newtons (N), d = distance in metres (m).
A car's brakes apply a force of 500 N and bring it to a stop after 23 m. Calculate the work done by the brakes.
$E = F \times d$
$E = 500 \times 23$
$E = 11500 J$
Describe the energy transfer that occurs when a bird flies through the air.
Energy is transferred from the bird's kinetic store to its thermal store, and dissipated to the thermal store of the surroundings due to air resistance.
Changes in ______ are related to gravitational potential energy, while changes in speed are related to kinetic energy.
Changes in height are related to gravitational potential energy, while changes in speed are related to kinetic energy.
True or False?
Work done and energy transferred are the same physical quantity.
True.
Work done = energy transferred.
Define gravitational potential energy.
The energy an object has due to its height in a gravitational field.
State the equation for the change in gravitational potential energy.
$Δ G P E = m \times g \times Δ h$
m = mass (kg), g = gravitational field strength (N/kg), Δh = change in height (m).
Define kinetic energy.
The amount of energy an object has as a result of its mass and speed.
State the equation for kinetic energy.
$K E = \frac{1}{2} \times m \times v^{2}$
m = mass (kg), v = speed (m/s).
A rollercoaster of mass 100 kg falls through a height of 15 m, with negligible friction. Calculate its maximum speed at the bottom (g = 10 N/kg).
$Δ G P E = m \times g \times Δ h = 100 \times 10 \times 15 = 15000 J$
$Δ G P E = K E$
$v = \sqrt{\frac{2 \times 15000}{100}} = 17 m/s$
In a ______ energy transfer, all of the gravitational potential energy is transferred to kinetic energy.
In a perfect energy transfer, all of the gravitational potential energy is transferred to kinetic energy.
True or False?
A swinging pendulum is a good example of a perfect energy transfer between its kinetic and gravitational potential stores.
True.
Energy is transferred back and forth between the kinetic and gravitational potential stores as the pendulum swings.
Define dissipated energy.
Energy that is spread out to the thermal store of the surroundings, usually as wasted energy.
Give three causes of unwanted heating in a system.
Air resistance, frictional forces and resistance in wires.
Explain why friction on a bicycle's gears and chain causes a wasted energy transfer.
Energy is transferred from the kinetic store of the bike to the thermal store of the gears and chain, so the rider must do more work to keep the bike moving.
How can friction between moving parts be reduced?
By lubricating the parts that rub together.
List two factors that affect the effectiveness of an insulator.
Its thermal conductivity and its thickness.
______ wall insulation reduces conduction of heat through the walls of a house from the inside to the outside.
Cavity wall insulation reduces conduction of heat through the walls of a house from the inside to the outside.
True or False?
A denser insulating material is generally a better insulator.
False.
The more dense the insulator, the more conduction can occur, so a less dense material insulates better.
Define power.
The rate of energy transfer, or the rate at which work is done.
Two cars accelerate to the same final speed, doing the same amount of work. What does it mean if one car has more power?
It transfers that energy, or does that work, in a shorter amount of time.
State the equation for power.
$P = \frac{E}{t}$
P = power (W), E = energy transferred (J), t = time (s).
An oven has a power of 2500 W and is used for 50 minutes. Calculate the energy transferred.
$t = 50 \times 60 = 3000 s$
$E = P \times t = 2500 \times 3000$
$E = 7500000 J$
Define the watt.
1 joule of energy transferred per second (1 W = 1 J/s).
1 kilowatt is equal to ______ watts.
1 kilowatt is equal to 1000 watts.
True or False?
Power can be described as work done per unit time.
True.
Since work done = energy transferred, power is also work done per unit time.
Define efficiency.
The ratio of the useful energy output from a system to its total energy output.
What is the difference between a system with high efficiency and one with low efficiency?
A high efficiency system transfers most of its energy usefully, with little wasted.
A low efficiency system wastes most of its energy, with only a small amount useful.
Give the two equations used to calculate efficiency.
$e f f i c i e n c y = \frac{useful energy transferred by the device}{total energy supplied to the device}$
$e f f i c i e n c y = \frac{useful power output}{total power input}$
Efficiency can be represented as a ______ or as a ______.
Efficiency can be represented as a decimal or as a percentage.
True or False?
Efficiency can be expressed in either joules or watts.
False.
Efficiency has no units - it is expressed only as a ratio (decimal) or a percentage.
How do you convert an efficiency ratio into a percentage?
Multiply the ratio by 100.
For example, a ratio of 0.25 gives a percentage efficiency of 0.25 × 100 = 25%.
What is the equation linking power, energy transferred and time?
$P = \frac{E}{t}$
where P is power, E is energy transferred and t is time.

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