Year 8 Science Revision: Energy and Electricity

Flashcards covering energy types, energy conservation, heat transfer mechanisms, renewable and non-renewable energy resources, fossil fuel formation, environmental impacts, and basic electricity concepts including series and parallel circuits, current, voltage, resistance, and electromagnets.

How is 'energy' defined in the revision guide?

Energy is a number used to describe a system (set of objects) that is always conserved and never changes.

What is the standard unit of energy?

The Joule ($\text{J}$).

What source gives off light energy?

Anything luminous gives off light energy (for example: the Sun, light bulbs, candles, and glow worms).

What produces sound energy?

Anything noisy gives off sound energy (for example: vocal cords, speakers, and musical instruments).

Where is electrical energy found?

Wherever there is an electric current flowing.

How does an object's temperature relate to its thermal (heat) energy?

Everything has some heat energy; the hotter something is, the more heat energy it has.

What type of energy is possessed by moving objects?

Kinetic (movement) energy.

What gives an object gravitational potential energy?

Being above the ground (anything that can fall, such as ski jumpers, planes, and climbers).

What kind of objects possess elastic energy?

Anything that has been stretched, such as rubber bands and springs.

What is chemical energy?

Stored energy that can be released by a chemical reaction, found in items like food, fuels, and batteries.

Which three types of energy are categorized specifically as stored energy?

Gravitational potential, chemical, and elastic energy.

What does the law of conservation of energy state?

Energy cannot be created or destroyed; it can only change from one form to another.

In what form is energy almost always lost during energy transfers?

As heat (thermal energy), meaning you never get as much useful energy out as you put in.

According to the energy transfer diagrams, how much energy is wasted as heat when $100\,\text{J}$ is input into the light bulb and the horse respectively?

For the light bulb, $80\,\text{J}$ is lost as wasted heat energy (with $20\,\text{J}$ useful light). For the horse, $85\,\text{J}$ is lost as wasted heat energy (with $15\,\text{J}$ useful energy).

What occurs during the process of convection?

Convection occurs when particles with a lot of heat energy in a liquid or gas move and take the place of particles with less heat energy.

How is heat transferred through conduction in a metal?

The hotter the metal, the more kinetic energy the vibrating atoms have. This kinetic energy is transferred from hotter parts of the metal to cooler parts.

What is thermal radiation and why can it travel through the vacuum of space?

Radiation is a type of electromagnetic radiation that involves waves. Because no particles are involved, it can travel through a vacuum.

What is the definition of a non-renewable fuel source?

A fuel source that has a long replacement time (much longer than a human lifetime).

What are the four non-renewable energy resources listed in the guide?

Coal, fossil fuel oil, natural gas, and nuclear energy.

What is the definition of a renewable energy source?

A fuel source with a short replacement time (within a human lifetime) that tends not to produce pollution or carbon dioxide.

Which five renewable energy resources are highlighted in the guide?

Solar energy, wind energy, hydropower energy, geothermal energy, and biomass energy.

What are the main advantages and disadvantages of renewable energy compared to non-renewable energy?

Renewable sources will never run out and produce little to no pollution, but they do not provide as much energy and can be unreliable if dependent on the weather. Non-renewable sources produce a lot of energy and do not rely on weather, but they will run out and emit carbon dioxide.

How was coal formed over millions of years?

Giant plants died in swamps before the dinosaurs and were buried under water and dirt. Over millions of years, enormous heat and pressure turned the dead plants into coal.

How were oil and natural gas deposits formed?

Tiny sea plants and animals died, fell to the ocean floor, and were buried under layers of silt and sand. Over millions of years, heat and pressure turned their remains into oil and gas.

What is the step-by-step process of generating electricity in a fossil fuel power station?

Fuel is burnt in a boiler releasing heat energy to heat water into steam; the steam drives turbines, which turn a generator to produce electrical energy.

What are the three components of the fire triangle, and what is the word equation for hydrocarbon combustion?

The fire triangle consists of Oxygen, Heat, and Fuel. The reaction is: $\text{Hydrocarbon} + \text{oxygen} \rightarrow \text{carbon dioxide} + \text{water}$.

How does burning fossil fuels contribute to global warming?

Fossil fuels are hydrocarbons that release carbon dioxide ($\text{CO}_2$) when burnt. The carbon dioxide traps heat from the Sun in the atmosphere, raising the Earth's average temperature.

What causes acid rain, and what harm does it cause?

Sulphur impurities in fossil fuels produce sulphur dioxide ($\text{SO}_2$) when burnt, which forms sulphuric acid ($\text{H}_2\text{SO}_4$) in clouds. Acid rain damages trees, aquatic creatures, and buildings.

What circuit component is represented by this symbol?

A fixed resistor.

What circuit component is represented by this symbol?

A variable resistor (or dimmer).

What electrical components do these two symbols represent?

A voltmeter (left) and a two-way switch / S.P.D.T. (Single Pole Double Throw switch) (right).

What is the distinction between an electrical conductor and an insulator?

Conductors allow electricity to pass through them (e.g., copper, iron, all metals). Insulators do not allow electricity to pass through them (e.g., rubber, plastic).

Why do bulbs become dimmer when wired in series, and what happens if one bulb is unscrewed?

Two bulbs in series have more resistance than a single bulb, so less current flows. If one bulb is unscrewed, the circuit is broken and all the other bulbs go out.

From which terminal does electric current flow in a circuit diagram?

Current flows away from the positive ($+)$) terminal (the long, thin line of the cell) toward the negative ($-$) terminal.

How do lamps behave when wired in parallel compared to series?

Lamps in parallel both stay bright, and if one is unscrewed the other remains lit; however, the cell drains faster because more total current flows.

What happens in a short circuit and why can it be dangerous?

Electricity takes the easiest route down a bypass wire, bypassing components so the lamps go out. A high current flows, which can quickly drain the battery and present a hazard.

What is electric current, and is it used up by components?

Current is the rate of flow of charge. It is not used up; the current flowing into a component equals the current flowing out.

What instrument and unit are used to measure electric current?

Current is measured using an ammeter connected in series, and its unit is amps (amperes, $\text{A}$).

What is voltage and how is it measured?

Voltage is a measure of potential difference delivered by charges to components. It is measured in volts ($\text{V}$) using a voltmeter connected in parallel across the component.

How must ammeters and voltmeters be positioned relative to circuit components according to this circuit diagram?

Ammeters must be placed in series within the circuit, while voltmeters must be connected in parallel around the component being measured.

What is electrical resistance, and what is its unit?

Resistance is the measure of difficulty electrons face when flowing through an object (analogous to friction slowing them down). It is measured in ohms ($\Omega$).

How do the length and thickness of a wire affect its electrical resistance?

The longer the wire, the greater the resistance; the thinner the wire, the greater the resistance.

What device is shown in this diagram, and what are its essential parts?

An electromagnet, constructed from a coil of insulated wire wrapped around an iron nail (soft iron core), connected to a battery and a switch.

What are three methods to increase the magnetic strength of an electromagnet?

1. Increase the current in the wire (add more batteries), 2. Add more turns of wire to the coil, 3. Add a soft iron core inside the coil.

Why are electromagnets useful, and what are three common practical applications?

They can be switched on and off easily. Useful applications include lifting objects in scrap yards, medical equipment, and relays.