Electricity and Magnetism

Electric current is measured in amperes (amps, A), using an ammeter. An ammeter is always connected in series in the circuit, so that all of the current being measured passes through it.

Step 1 — State the formula:

$$ Q = I \times t $$

Step 2 — Substitute the values:

$$ Q = 2 \times 30 $$

Answer: $Q = 60\,\text{C}$ (coulombs)

Step 1 — Choose a suitable interval:

Between $t=0$ and $t=20\,\text{s}$: $\Delta Q = 40 - 0 = 40\,\text{C}$, $\Delta t = 20 - 0 = 20\,\text{s}$.

Step 2 — Apply $I = \frac{Q}{t}$:

$$ I = \frac{40}{20} $$

Answer: $I = 2\,\text{A}$. (Each $5\,\text{s}$ interval also gives $\frac{10}{5}=2\,\text{A}$, confirming the current is constant.)

Benefit: If a fault causes an unusually high current to flow (for example, a short circuit), a fuse or circuit breaker automatically cuts off the current within a fraction of a second. This prevents wires from overheating, which greatly reduces the risk of electrical fires and protects both the household wiring and the appliances connected to it.

Drawback: A blown fuse must be identified and replaced (or a tripped breaker reset) before the circuit works again, which is inconvenient and can leave part of a home without power until it is fixed. If people don't know how to safely reset it, or repeatedly replace a fuse with one rated too high just to stop it blowing, the safety protection can be lost.

Benefit: A multi-socket adaptor is very convenient, allowing several appliances to run from a single wall socket without needing extra wiring installed in the home.

Drawback: The total current drawn is $6+5+4=15\,\text{A}$, which is more than the socket's $13\,\text{A}$ rating. Drawing more current than a circuit is designed for causes the wires to heat up more than intended, which is a genuine fire risk — overloading sockets and adaptors like this is a common cause of household electrical fires, which is why appliances should be spread across multiple circuits rather than overloading one.

Benefit: Generating electric current from renewable sources such as wind and solar produces far less carbon dioxide and other pollution than burning coal or gas, helping to reduce the environmental impact of the huge amount of electricity modern society depends on, and reducing reliance on finite fossil fuel resources.

Concern: Renewable sources are less predictable — wind turbines generate no current when there is no wind, and solar panels generate little at night or in cloudy weather. Since hospitals, transport systems, and homes need a continuous, reliable current at all times, this intermittency raises real concerns about power cuts unless it is paired with large-scale energy storage (such as batteries) or backup supplies, which is expensive and still being developed at the scale required.

If one of the bulbs in this series circuit breaks (its filament fails), the circuit is no longer a complete loop. Since there is only one path for current, breaking it anywhere stops current everywhere — so both bulbs go out, even though only one bulb actually failed.

If one bulb breaks, its branch is broken — but the other branch is a separate, complete path back to the battery. Current can still flow through the working bulb, so it stays lit, unaffected by the broken one.

At the junction where the branches meet, the current splitting into the branches must add back up to the current leaving the battery (charge is conserved — none is lost or gained at the junction):

$$ A = A_1 + A_2 = 0.30 + 0.50 $$

Answer: $A = 0.80\,\text{A}$

In a series circuit, the potential difference (voltage) of the battery is shared between the components, so the individual voltages must add up to the total: $$ V_1 + V_2 = V_{battery} $$ $$ 3.5 + V_2 = 9 $$ Answer: $V_2 = 5.5\,\text{V}$

The readings are all the same, within normal measurement uncertainty ($0.44$–$0.45\,\text{A}$, a difference easily explained by reading a scale to the nearest small division). This confirms that in a series (single-loop) circuit, the current is the same at every point around the loop.

Benefit: In a parallel circuit, each appliance or light is on its own independent branch and receives the full mains voltage regardless of what else is switched on. If one appliance breaks or is switched off, the others keep working normally — imagine if a whole house went dark every time one light bulb blew, as would happen in series!

Drawback: Parallel wiring requires much more cable (a separate path back to the supply for each branch/circuit) compared to a single simple loop, which increases the cost and complexity of installing the electrics in a building.

Benefit: If one LED fails in a parallel string, only that LED goes out — the rest of the string keeps working, since each LED has its own independent path to the supply. This makes faults far easier to notice and fix, and is much less frustrating for the user than a whole string going dark.

Drawback: A parallel design needs more wiring to give every LED its own connection to both supply wires, which increases the manufacturing cost and complexity of the light string compared to a single simple series loop.

Benefit: If a fault occurs on one circuit (for example, a short circuit in a kitchen appliance), only that circuit's breaker trips, cutting power to just that part of the building. The rest of the house — lighting, other rooms — keeps working normally, which is both safer (the fault is isolated) and more convenient than losing power to the whole building.

Drawback: This design is more complex and expensive to install than a single circuit for the whole building, since it requires multiple breakers, more cable runs, and careful planning by an electrician to decide which sockets and lights belong to which circuit — increasing both material and labour costs.

$$ V = IR $$ where $V$ is potential difference (voltage) in volts (V), $I$ is current in amps (A), and $R$ is resistance in ohms ($\Omega$).

Step 1 — State the formula:

$$ V = IR $$

Step 2 — Substitute the values:

$$ V = 2 \times 5 $$

Answer: $V = 10\,\text{V}$

Rearranging $V = IR$ for resistance: $$ R = \frac{V}{I} = \frac{12}{3} $$Answer: $R = 4\,\Omega$

$$ R = \frac{V}{I} = \frac{4}{0.5} $$Answer: $R = 8\,\Omega$

Benefit: Resistive heating elements convert electrical energy directly and efficiently into heat, with a simple, reliable design and no moving parts — making appliances like kettles and toasters fast, convenient, and relatively cheap to manufacture.

Drawback: A high-resistance element carrying a large current gets very hot, so a fault (such as damaged insulation or a short circuit) creates a genuine fire risk. Using these appliances also uses a significant amount of electrical energy, contributing to household energy costs and, depending on how the electricity is generated, to environmental impact.

Benefit: Reducing the current in the long transmission cables reduces the energy wasted as heat in the cables' own resistance. This means significantly more of the generated electrical energy actually reaches homes and businesses usefully, rather than being wasted, making the whole electricity supply system more efficient.

Drawback: Very high voltages are dangerous, so this approach requires expensive infrastructure — tall pylons, thick insulation, and transformers to safely step the voltage up and back down — as well as strict safety measures and exclusion zones around power lines to protect the public, adding significant cost and land use.

Benefit: Electric heating provides convenient, controllable warmth on demand, which can be important for health and comfort — particularly for elderly or vulnerable people in cold weather, or for medical uses such as warming a patient. Unlike some other heating methods, it produces no smoke or fumes at the point of use.

Concern: Because resistive heating relies on a large current flowing through a resistive element, any fault — a damaged cable, a covered heater restricting airflow, or a compressed/damaged heating wire in a blanket — can cause dangerous overheating and a fire hazard. There is also an ongoing energy and environmental cost: heaters can use a large amount of electricity, and if that electricity is generated from fossil fuels, this adds to carbon emissions, so the convenience of resistive heating needs to be balanced against these safety and environmental considerations.

Magnetic: iron, steel, nickel, cobalt (these are all ferromagnetic materials/alloys). Non-magnetic: copper, aluminium, plastic, wood.

A magnetic field is the region around a magnet (or magnetic material) in which it can exert a magnetic force. By convention, magnetic field lines are drawn pointing from the north (N) pole to the south (S) pole outside the magnet, with arrows showing this direction.

The materials attracted to the magnet (iron, steel, nickel) are all ferromagnetic materials — iron itself, or alloys/elements closely related to it. The materials not attracted (copper, plastic, wood) are all non-magnetic. This shows only a small group of materials are magnetic, not metals in general (copper is a metal but is not attracted).

Benefit: A magnetic separator can quickly and automatically pull out steel and iron objects from a large, fast-moving stream of mixed waste, without needing anyone to sort it by hand. This makes recycling ferrous (iron-containing) metal far more efficient, reduces landfill waste, and saves the energy and raw materials needed to mine and produce brand-new steel.

Drawback: A simple magnet only attracts magnetic metals like steel and iron — non-magnetic metals such as aluminium and copper are left behind and pass straight through, so additional separation methods (and additional cost/equipment) are still needed to fully sort all recyclable materials.

Benefit: A magnetic compass needs no batteries, satellites, or signal — it works purely using the Earth's own magnetic field, making it a simple, reliable backup that keeps working in remote areas or during power/technology failures where GPS might not be available.

Drawback: A compass can be thrown off by nearby magnetic materials or other magnetic fields (for example, being near a car, an electronic device, or a deposit of magnetic rock), giving an inaccurate reading without the user realising. It is also far less precise than GPS, which can pinpoint an exact location rather than just a direction.

Benefit: Magnetic storage allows huge amounts of data to be stored very cheaply per gigabyte, and — unlike some memory types — it is non-volatile, meaning the stored data is retained even with no power connected, which is essential for reliably keeping files, photos, and programs long-term.

Concern: Because the data relies on tiny magnetised regions, exposing a hard drive to a sufficiently strong external magnetic field can corrupt or erase the stored data — an important risk for anyone storing important files this way. There is also an environmental concern: as hard drives are replaced (increasingly by non-magnetic solid-state drives), the discarded devices contribute to growing electronic waste unless properly recycled.

1. Number of turns of wire: more turns in the coil produces a stronger magnetic field. 2. Size of the current: a larger current flowing through the coil produces a stronger magnetic field. 3. Core material: using a magnetic core (such as soft iron) inside the coil, instead of no core (air), greatly concentrates and strengthens the field.

Soft iron magnetises quickly and strongly when current flows, but loses its magnetism almost immediately once the current is switched off. Steel would stay magnetised even after the current stopped, meaning the electromagnet could not be switched off — this would make it useless for applications like a scrapyard crane, which needs to release its magnetised load by switching the current off.

Reversing the battery terminals reverses the direction the current flows through the coil. This reverses the direction of the magnetic field the coil produces, which swaps the electromagnet's poles — whichever end was the north pole becomes the south pole, and vice versa.

The data shows a clear pattern: more turns in the coil means more paperclips picked up. The relationship is directly proportional — paperclips picked up $=\ \text{turns}\div5$ in every case ($10\div5=2$, $20\div5=4$, $30\div5=6$, $40\div5=8$), confirming that increasing the number of turns increases the electromagnet's strength.

Benefit: An electromagnetic crane can quickly and efficiently lift heavy loads of scrap steel/iron and precisely control when to release them (by switching the current off), which is far faster and safer for workers than using mechanical grabs or hooks, and allows magnetic scrap to be automatically separated from non-magnetic material.

Drawback: Powerful electromagnets require a large, continuous supply of electrical current to stay switched on, using significant amounts of energy. There is also a safety risk if power to the electromagnet fails or is interrupted unexpectedly while a heavy load is suspended — the load would suddenly drop.

Benefit: MRI scanners allow doctors to see detailed, high-quality images of soft tissue, organs, and injuries inside the body without exposing the patient to ionising radiation (unlike X-rays or CT scans), making them a safer imaging option that can be used more freely, including repeated scans, to diagnose and monitor a wide range of medical conditions.

Concern: The magnetic fields used are extremely strong, which raises real safety risks: loose metal objects can become dangerous flying projectiles near the scanner, and the strong field can be dangerous for patients with certain metal implants or devices such as pacemakers. MRI machines are also very expensive to build, install, and run (the powerful electromagnets often require special cooling), limiting how widely available this technology can be, especially in areas with fewer healthcare resources.

Benefit: Electromagnets, through the motor effect, are at the heart of technologies that have transformed daily life and communication — from loudspeakers that let us hear music and calls, to electric motors that power everything from washing machines to electric vehicles. Electric vehicles in particular can reduce local air pollution and emissions compared to petrol/diesel vehicles, improving air quality where they are used.

Drawback: The overall environmental benefit depends heavily on how the electricity used is generated — if it still comes largely from burning fossil fuels, much of the emissions problem is simply moved elsewhere rather than solved. Building these devices, including the powerful magnets and batteries involved, also requires mining and processing raw materials, which has its own environmental and social costs, and contributes to electronic waste at the end of a device's life.