Energy, Work & Power (Cambridge (CIE) IGCSE Co-ordinated Sciences (Double Award): Physics): Flashcards

The four energy transfer pathways used in physics are:

• mechanical

• electrical

• heating

• radiation

True.

An example of energy transfer by heating is a hot chocolate warming up cold hands.

Kinetic energy is the energy an object possesses due to its motion, determined by its mass and speed.

True.

Any object in motion possesses kinetic energy.

The equation for calculating kinetic energy is

Where:

• = kinetic energy, measured in joules (J)

• = mass, measured in kilograms (kg)

• = velocity, measured in metres per second (m/s)

False.

Kinetic energy is measured in units of joules (J).

In the kinetic energy equation, represents the speed of the object in meters per second (m/s).

In the kinetic energy equation, represents the mass of the object in kilograms (kg).

Kinetic energy can be calculated by multiplying half of the object's mass by the square of its speed.

Gravitational potential energy is the energy possessed by an object due to its height in a gravitational field.

False.

Energy is transferred to an object's gravitational potential store when it is lifted.

The equation for calculating gravitational potential energy is

Where:

• = change in gravitational potential energy, measured in joules (J)

• = mass, measured in kilograms (kg)

• = gravitational field strength, measured in newtons per kilogram (N/kg)

• = change in height in metres (m)

False.

Gravitational potential energy is measured in units of joules (J).

In the gravitational potential energy equation, represents the mass of the object in kilograms (kg).

In the gravitational potential energy equation, represents the gravitational field strength in newtons per kilogram (N/kg).

False.

Energy is transferred away from an object's gravitational potential store when it falls.

When an object is lifted, work is done against the weight force acting on the object, so energy is transferred to its gravitational potential store.

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

Work done is the product of the force applied to an object and the distance moved in the direction of the force. It is measured in joules (J) or newton metres (N m).

False.

The total amount of energy in a closed system remains constant; it cannot be created or destroyed.

False.

Work is only done when the force causes the object to move a distance in the direction of the force. If there is no movement, no work is done.

An energy flow diagram shows the energy stores and the energy transfers taking place within a system.

The equation for work done is:

Where:

• = work done, measured in joules (J) or newton metres (N m)

• = force, measured in newtons (N)

• = distance moved in the direction of the force, measured in metres (m)

The energy is related by:

total energy in = useful energy out + wasted energy

True.

When work is done, energy is transferred, so the energy transferred (J) is equal to the work done (J).

Energy is dissipated (spread out) to the surroundings by heating and radiation. This energy is often not useful, so it is described as wasted energy.

1 joule (J) is equal to 1 newton metre (N m).

True.

Work is done against the ball's weight as it is lifted, so energy is transferred to its gravitational potential store.

Power is the rate at which energy is transferred or work is done, measured in watts (W).

False.

Power refers to the rate at which energy is transferred or work is done, not the total amount of energy transferred.

False.

A car has more power if it does the same amount of work in a shorter amount of time.

The formula for calculating power is:

or

Where:

• = power, measured in watts (W)

• = work done, measured in joules (J)

• = energy transferred, measured in joules (J)

• = time, measured in seconds (s)

The rate of doing work, or power, refers to the amount of work done or energy transferred per unit time. It is measured in watts (W).

False.

Power is the rate at which energy is transferred or work is done, work done is the total amount of energy transferred.

The formula for calculating energy transferred using power is:

Where:

• = = work done or energy transferred, measured in joules (J)

• = power, measured in watts (W)

• = time, measured in seconds (s)

False.

Power is typically measured in watts (W), while energy is measured in joules (J).

Efficiency is a measure of the amount of useful power or energy output from a system compared to its total power or energy input. It is often expressed as a percentage.

True.

Efficiency measures how much power or energy is transferred usefully, compared to the total power or energy input. Therefore, it is also a measure of how much energy or power is wasted.

True.

The overall efficiency of a typical coal-fired thermal power station is 30%.

False.

The higher the efficiency of an energy transfer, the less energy is wasted.

Efficiency is calculated as the ratio of useful power or energy output to total power or energy input, usually expressed as a percentage.

The equation for calculating efficiency is:

True.

Efficiency can be expressed as a ratio between 0 and 1, or as a percentage between 0 and 100%.

False.

Efficiency is a ratio and therefore a dimensionless quantity that does not have any units.

True.

If an energy transfer is 65% efficient, then 35% of the energy is wasted.

The primary source of energy for most of Earth's energy resources is the Sun.

True.

The Sun heats up the atmosphere, creating wind and producing waves.

False.

Geothermal is an energy form that comes from the heating of rocks by the Earth's core and not from the Sun.

Solar cells, also known as photovoltaic cells, are devices made of semiconducting materials that produce electricity from sunlight in a process called the photoelectric effect.

True.

Solar energy is considered renewable because it is derived from the Sun which is expected to continue shining for billions of years.

Solar energy is transferred to the Earth by radiation, in the form of visible light and infrared radiation.

False.

Solar panels produce no greenhouse gases or pollution once they are operating.

Solar panels are devices that transfer energy from sunlight to the thermal store of the panels, which is then used to heat water.

Advantages of solar energy include:

• renewable

• reliable in hot climates

• produce no greenhouse gases or pollution

• Can be used in remote areas

Solar furnaces consist of large curved mirrors that focus sunlight onto a small area, which heats water to produce steam, which then turns turbines which generate electricity.

False.

Solar farms need to be large-scale to produce significant amounts of electricity.

Fossil fuels are natural resources formed over millions of years from the remains of plants and animals.

The three main fossil fuels are:

• coal

• oil

• natural gas (methane)

False.

Burning fossil fuels produces carbon dioxide which is a greenhouse gas that contributes to global warming. But other harmful gases are also released in the combustion of fossil fuels, such as sulphur dioxide which causes acid rain.

The disadvantages of using fossil fuels include:

• non-renewable (so will run out)

• produce carbon dioxide which contributes to global warming

• produce sulphur dioxide which causes acid rain

The main uses of fossil fuels are transportation, electricity generation, and heating in homes and industries.

True.

It takes millions of years for fossil fuels to form. This is why they are considered a non-renewable energy resource.

Energy is transferred from the chemical store of the fossil fuel during combustion. This energy originally came from sunlight and was transferred to plants and animals through photosynthesis.

Biofuels are produced from plant matter, such as crops, which undergo processes like fermentation or distillation to extract ethanol or methane for use as alternative fuels to fossil fuels.

The main advantages of biofuels are:

• renewable

• carbon neutral

True.

Nuclear power stations do not release pollution into the atmosphere during normal operation.

Nuclear fuel refers to materials, such as uranium, used in nuclear reactors to release energy in nuclear fission reactions.

Nuclear power stations generate electricity by using the energy released in nuclear fission reactions to heat water to produce steam. The steam then turns turbines connected to generators, which produce electricity.

Nuclear fuel is a non-renewable resource because there is a finite supply of uranium ore found in the ground.

Wave and tide power harnesses the energy from the rise and fall of waves or tides to generate electricity, typically using turbines.

False.

Wave and tidal power do not produce pollution.

The main advantage of wave and tide power is that they are renewable energy resources that produce no pollution.

Wave and tidal power stations generate electricity by utilising the motion of waves or tides to turn turbines, which then generate electricity through electromagnetic induction.

Hydroelectric dams are structures built across rivers to store water at a height in reservoirs. The water can be released, flowing over a turbine that turns a generator that generates electricity.

True.

Hydroelectric dams can release significant amounts of greenhouse gases due to the decomposition of organic matter in flooded areas, or due to the fuels used to pump the water back up to the reservoir.

The main disadvantage of hydroelectric dams is that they require valleys to be flooded. This results in the destruction of habitats, towns, and villages.

The main advantage of hydroelectric dams is their ability to respond to electricity demand quickly and reliably.

Geothermal energy is energy stored in the thermal store of rocks beneath the Earth's surface from tectonic heating. The hot rocks are used to heat water that can be used as a hot water supply and to produce steam to turn turbines for electricity generation.

False.

Geothermal energy is considered a renewable resource.

The main advantage of geothermal energy is its reliability and renewability. It offers a consistent source of heating and electricity production.

The main disadvantage of geothermal energy is the limited availability of suitable locations for large-scale electricity production.

Geothermal energy generates electricity by heating water and generating steam using the hot rocks beneath the Earth's surface, which drives turbines to produce electricity.

Geothermal energy is a renewable energy resource. This means it can be replenished naturally and is sustainable over the long term.

Nuclear fission is the process in which a large nucleus is split into smaller nuclei, releasing a large amount of energy.

Nuclear fusion is the process in which small nuclei are joined to form a larger nucleus, releasing a large amount of energy.

In nuclear fusion, small nuclei are joined to form larger nuclei. In nuclear fission, large nuclei are split into smaller nuclei.

False.

The Sun releases energy by nuclear fusion, in which small nuclei join to form larger nuclei.

Nuclear fusion requires extremely high temperatures and pressures, which can normally only be found in the core of a star.