Electricity and Circuits

Electric charge is a property of particles that causes electrical forces. Protons carry positive charge and electrons carry negative charge. Opposite charges attract, while like charges repel. Charge is measured in coulombs (C).

Electric current is the rate at which electric charge flows through a conductor. It is measured in amperes (A). Formula: I = Q/t, where I is current, Q is charge and t is time. In metal wires, electrons move through the conductor.

Voltage is the energy transferred per unit of electric charge between two points. It is measured in volts (V). Formula: V = E/Q. A battery supplies potential difference, which drives current around a complete circuit.

Resistance describes how strongly a component opposes electric current. It is measured in ohms (Ω). For a fixed voltage, increasing resistance reduces current. Resistance depends on factors including material, wire length, cross-sectional area and temperature.

For an ohmic conductor at constant temperature, voltage is proportional to current. Formula: V = IR, where V is voltage, I is current and R is resistance. Example: 12 V across a 4 Ω resistor produces 3 A of current.

A complete or closed circuit provides an unbroken conducting path for current. An open circuit contains a break, preventing current through that path. Closing a switch completes the circuit; opening it interrupts the path.

In a series circuit, components are connected along one path. The same current flows through every component, while the supply voltage is shared. Total resistance is the sum of individual resistances: Rtotal = R1 + R2 + ... .

In a parallel circuit, components occupy separate branches. Each branch has the same voltage across it, while the total current is divided between branches. If one branch opens, other complete branches can continue operating.

Identical bulbs connected in series to the same battery are generally dimmer than a single bulb because total resistance increases and current decreases. Identical bulbs connected in parallel each receive the supply voltage and can maintain their brightness.

A switch controls whether a conducting path is complete. In a simple series circuit, opening the switch stops current throughout the circuit. In parallel arrangements, different switches can control separate branches.

An OR-switch arrangement places two switches in parallel so either switch can complete the path to a lamp. The lamp lights if switch A OR switch B is closed. It remains off only when both switches are open.

Conductors allow electric charge to move relatively easily; metals such as copper are good conductors. Insulators resist charge movement; examples include plastic and rubber. Insulating materials help prevent unintended contact with live conductors.

Electrical power is the rate at which electrical energy is transferred. It is measured in watts (W). Formula: P = VI. For a resistor, P = I²R or P = V²/R. A device using 2 A at 12 V consumes 24 W.

A permanent magnet produces a magnetic field without requiring an external electrical supply. Every magnet has north and south poles. Like poles repel and unlike poles attract. Magnetic effects are strongest near the poles.

A magnetic field is a region where magnetic forces act on magnets, magnetic materials or moving charges. Field lines show the field direction; outside a bar magnet they point from north to south. Closer lines indicate a stronger field.

Iron filings placed around a magnet align with its magnetic field, revealing the field pattern. The filings cluster more closely near the poles, showing regions of stronger magnetic field. A compass can indicate the local field direction.

Ferromagnetic materials such as iron, nickel and cobalt are strongly attracted to magnets and can become magnetised. Materials respond differently to magnetic fields, so not every metal is strongly magnetic.

An electric current creates a magnetic field around a conductor. Around a straight wire, the field forms circular patterns. Reversing current reverses the magnetic field direction. This links electricity and magnetism.

For conventional current in a straight wire, point your right thumb in the direction of current. Your curled fingers show the direction of the circular magnetic field. Conventional current is opposite to electron movement in a metal.

An electromagnet uses electric current to produce a magnetic field, commonly through a coil of wire. Increasing current or the number of turns generally strengthens the field. A suitable iron core can strengthen it further.

When current passes through a coil, the magnetic fields from individual turns combine. A solenoid produces a field similar to a bar magnet, with north and south ends. Reversing the current reverses the coil's magnetic polarity.

Reversing the direction of current through a wire or coil reverses the direction of its magnetic field. This can be demonstrated using a compass near the conductor. The effect is important in understanding electromagnetic devices.

The workshop experiments explore how components behave in complete circuits, how bulbs respond to series and parallel connections, how switches control current, and how magnetic fields behave around magnets and current-carrying conductors. For exam revision, focus on the observation and its physical explanation.

Electrical systems supply and control radiotherapy equipment. Accelerating voltages and electron currents are important in X-ray generation, while magnetic fields are used in equipment such as MRI systems. Understanding circuits and electromagnetism supports safe operation and interpretation of medical technology.