Energy Resources & Power Transmission (OCR GCSE Physics A (Gateway)): Flashcards

A reliable energy resource is an energy source that can produce energy at any time, regardless of weather or environmental conditions. Fossil fuels and nuclear fuel are examples of reliable sources.

False.

Wind power is not reliable because it can only generate electricity when it is windy. Non-reliable resources can only produce energy some of the time.

Of the three main fossil fuels, coal produces the most carbon dioxide, while natural gas produces the least. Switching to gas reduces carbon emissions, though it is not a long-term solution for reaching carbon neutrality.

The Greenhouse Effect is caused by increased concentrations of greenhouse gases, mainly methane and carbon dioxide, which trap infrared radiation in the Earth's atmosphere.

The Sun's rays enter the atmosphere and infrared radiation is emitted from the Earth's surface. Greenhouse gases absorb some of this radiation, trapping it in the atmosphere rather than letting it escape into space. The higher the concentration of greenhouse gases, the greater the temperature rise.

The Greenhouse Effect is the process by which greenhouse gases (mainly methane and carbon dioxide) absorb infrared radiation emitted from Earth's surface and trap it in the atmosphere, causing the planet's average temperature to rise.

True.

Over this period, fossil fuel use dropped from 75% to 38%, while renewable energy grew from 2% to 35%, reflecting the gradual shift towards cleaner energy technologies.

Complete the table of consequences of global warming.

Science can identify the environmental problems caused by energy use, but decisions about how to respond involve trade-offs between cost, public support, energy reliability and international cooperation. These are political, social and economic decisions, not purely scientific ones.

The National Grid is a system of cables and transformers linking power stations to consumers (houses, factories and buildings) across the UK, used to distribute electrical power.

False.

Step-up transformers increase the voltage (and reduce the current) before transmission. Step-down transformers then decrease the voltage for domestic use.

High potential difference means the same power can be transmitted at a much lower current (from P = IV). Lower current produces less heating in the cables, reducing energy loss and making the National Grid more efficient.

In the National Grid, step-up transformers increase the voltage, which decreases the current and reduces energy lost as heat in the cables.

A step-up transformer is one that increases the potential difference (and decreases the current). Used in the National Grid to raise voltage from the power station before transmission through power lines.

A step-down transformer is one that decreases the potential difference (and increases the current). Used in the National Grid to reduce voltage from transmission cables to safe levels for domestic use.

True.

When current is high, the cables heat up more, wasting more energy. This is why the National Grid uses high voltage (and low current) for transmission to minimise energy loss.

Complete the table for the National Grid voltage relationship.

Step-down transformers reduce the high voltage used in transmission cables down to much lower voltages suitable for homes, offices and shops. This makes the electricity safe for domestic and commercial use.

Alternating current (AC) is a type of current that changes direction repeatedly. Power stations produce AC, which is used in the National Grid and in homes. Transformers only work with AC.

True.

Transformers require alternating current to function. Power stations produce AC, which is why it is used throughout the National Grid and in homes.

A step-up transformer increases the voltage and decreases the current in the power cables. Lower current means less heating in the wires, so less energy is lost during transmission. This means more energy reaches consumers, increasing the efficiency of the National Grid.

Step-up transformers increase the potential difference, while step-down transformers decrease the potential difference for domestic use.

A transformer is a device used to increase or decrease the potential difference of AC electricity. Step-up transformers raise voltage before transmission; step-down transformers lower voltage for consumers.

Complete the table showing transformer roles.

False.

A step-up transformer increases the voltage but decreases the current. Voltage and current change in opposite directions in a transformer.

Transformers are used to: (1) increase the potential difference from power stations before transmission through the National Grid; (2) decrease the high voltage of transmission cables to safe levels for homes and businesses; (3) lower mains voltage further for electronic devices via adapters.

A step-up transformer is one that increases the potential difference from the primary coil to the secondary coil, while decreasing the current.

True.

Because P = IV, increasing voltage while keeping power constant means a smaller current flows. Less current means less heating in the cables.

When electricity is transmitted over large distances, the current in the wires heats them, resulting in energy loss.

Electricity is transmitted at high voltage to reduce the current in the cables. A smaller current produces less heat, which reduces energy loss during transmission.

The iron core (transformer) is the part of a transformer that links the primary and secondary coils. Iron is used because it is easily magnetised, allowing the changing magnetic field to pass through efficiently.

False.

An ideal transformer conserves energy, so input power equals output power. Increasing voltage reduces current by the same factor — power stays the same.

An alternating current in the primary coil produces a continuously changing magnetic field. This changing field passes through the iron core into the secondary coil, inducing an alternating potential difference.

Ideal Transformer Equation: V_p × I_p = V_s × I_s

Using V_p × I_p = V_s × I_s:

115 × I_p = 230 × 5

I_p = 10 A

The primary current is larger because the primary voltage is lower.

Direct current (d.c.) is a current that flows steadily in one direction around a circuit, from positive to negative. Cells and batteries produce d.c.

True.

In a.c., the current reverses direction repeatedly. In d.c., the current always flows the same way around the circuit.

The frequency of an alternating current is the number of times the current changes direction back and forth each second.

UK mains electricity has a frequency of 50 Hz and a potential difference of around 230 V. It is an alternating current (a.c.) supply.

Alternating current (a.c.) is a current that continuously changes direction, going back and forth around a circuit. Mains electricity is an a.c. supply.

False.

A d.c. supply has a fixed positive terminal and a fixed negative terminal. It is the a.c. supply whose terminals alternate between positive and negative.

Alternating current shows as a wave (sinusoidal pattern) on the oscilloscope, because the current regularly reverses direction. Direct current appears as a flat horizontal line.

AC vs DC Comparison

Mains electricity uses a.c. because it can be stepped up to high voltage using transformers for efficient transmission through the National Grid, then stepped back down for safe use. Transformers require a changing (alternating) current to operate.

The live wire is the wire in a mains cable that carries the alternating potential difference from the supply to the circuit. Coloured brown and the most dangerous of the three wires.

True.

The neutral wire is blue and forms the other end of the circuit from the live wire, completing the electrical circuit through the appliance.

In the UK, mains electricity is an alternating current supply with a frequency of 50 Hz and a potential difference of about 230 V.

The brown wire is the live wire — it carries the alternating potential difference. The blue wire is the neutral wire — it completes the circuit. The green and yellow striped wire is the earth wire — it is a safety wire to prevent electrocution.

The earth wire is a safety wire in a mains cable coloured green and yellow stripes. It does not normally carry current but provides a low-resistance path to earth if a fault occurs, preventing electric shocks.

False.

The earth wire only carries current if there is a fault in the appliance. Under normal conditions it carries no electricity — it is there for safety only.

A frequency of 50 Hz means the direction of the current changes back and forth 50 times every second. This is a property of alternating current supplied by the National Grid in the UK.

Three-Core Mains Cable

Mains electricity is alternating current, so it does not have fixed positive and negative sides. The live and neutral wires act as the two ends of the circuit, with the live wire carrying the changing potential difference and the neutral wire completing the circuit.

The live wire voltage is approximately 230 V.

False.

Even when a device is switched off, the live wire remains at 230 V if the mains supply is on. Touching it can still cause a lethal electric shock.

If the live wire touches a metal appliance case, the earth wire provides a low resistance path to the earth, causing a surge of current that melts the fuse.

The live wire operates at 230 V. If an electrician touches a live wire while their body is at 0 V (earth potential), a large current passes through them to reach earth, which can cause a lethal electric shock.

True.

The neutral wire has a voltage close to 0 V, so the potential difference between it and earth is very small. The live wire at 230 V poses a far greater risk of electrocution.

Wire Voltages and Safety

If the live wire contacts a metal case, the earth wire provides a low-resistance path to earth. This causes a surge of current through the fuse, which melts and breaks the circuit — cutting off electricity to the appliance and making it safe to touch.