LearnLah
Forces & PressureElectricity & CircuitsChemical Reactions, Acids & BasesPhotosynthesis & NutritionTransport & RespirationReproductionInteractions & Ecosystems

Study notes

Electricity & Circuits

Current and voltage as distinct ideas, how series and parallel circuits behave differently, and the difference between conductors and insulators, plus basic safety.

Learn it step by step

Current is the flow, voltage is the push

Electric current is the flow of electric charge through a conductor, measured in amperes. Voltage (potential difference) is the "push" or driving force that makes charge flow around a circuit, measured in volts. These are two different quantities, not two names for the same thing.

Conductors let current flow, insulators block it

Metals such as copper are good conductors, they allow charge to flow through them easily, which is why copper is used inside electrical wires. Materials such as rubber, dry wood, and plastic are insulators, they resist the flow of charge, which is why plastic is used to cover the outside of wires safely.

A series circuit has only one path

In a series circuit, all components share a single loop. If one bulb is removed or fails, the only path is broken, so every other bulb in that loop goes out too, current stops flowing everywhere.

A parallel circuit gives each branch its own path

In a parallel circuit, each bulb sits on its own separate branch back to the cell. Removing or breaking one branch only affects that branch, the other bulbs keep working normally because their own paths are still complete.

More cells in series means more voltage, and a brighter bulb

Cells connected in series add their voltages together, giving a bigger "push" that drives more current through the circuit. With everything else unchanged, adding a cell in series makes a bulb glow brighter.

More bulbs in the SAME series loop means a dimmer bulb

Adding more bulbs to a single series loop, without adding more cells, means the same driving voltage must now push current through more components, so less current flows and each bulb glows more dimly than before.

1 bulb in series53 bulbs in series, same cell2same voltage shared across more bulbs means each glows dimmer
Adding bulbs to the same series loop dims each bulb; adding a branch in parallel does not.

Water plus electricity is dangerous because water conducts

Water, especially with dissolved substances such as salts, is a conductor. It can provide an unintended path for current, so touching a live switch or socket with wet hands, or standing in water near a live source, greatly increases the risk of a shock.

Worked examples

A parallel circuit has two bulbs, each glowing brightly on its own separate branch. A third identical bulb is added on a new branch, also connected back to the same cell. Explain what happens to the brightness of the original two bulbs.
  1. A common misconception is that adding any bulb always dims the others, this is true in series but not in parallel.
  2. In a parallel circuit, each bulb sits on its own separate branch that forms a complete loop back to the cell on its own.
  3. Each branch is still driven by the cell's full voltage, independent of how many other branches exist.
  4. So the original two bulbs are unaffected and stay exactly as bright as before, even though the cell now supplies more total current overall.
A classmate says "current gets used up as it flows around a series circuit, so less current flows out of a bulb than flows into it." Explain why this is incorrect.
  1. The idea that current is "used up" like fuel is a common but incorrect way of thinking about circuits.
  2. In a series circuit there is only one loop, so the same current flows at every single point around that loop, into and out of every bulb.
  3. What DOES get transferred and "used up" along the way is energy, not current.
  4. The bulb converts some of that energy into light and heat, but the current itself stays the same all the way around.
A torch normally uses one cell and glows dimly. The same torch is then fitted with two cells in series and the same bulb. Explain what happens to the brightness, and why.
  1. It might seem like adding a second cell would simply share the current between the two cells and make things dimmer, but that is not how cells in series work.
  2. Two cells connected in series add their voltages together, giving a greater overall "push" driving the current.
  3. A greater voltage drives more current through the same single bulb.
  4. So the bulb glows brighter with two cells in series than with one, because the current flowing through it has increased.
A student removes the plastic insulating sleeve from a connecting wire, believing this will "help current flow better." Explain whether this reasoning is correct.
  1. The reasoning assumes the plastic covering somehow blocks or slows down the current inside the wire.
  2. In fact, current flows through the copper core inside the wire, and the plastic covering is only an insulator on the OUTSIDE.
  3. Removing the plastic sleeve does not change the copper core at all, so it gives no electrical benefit to how well current flows.
  4. What it does do is expose the live conductor, creating a shock hazard, so removing it is unsafe with no upside.

Mind map

Mind map for Electricity and Circuits.

  • Current vs voltage
    • current: flow of charge, amperes
    • voltage: the push, volts
  • Series circuits
    • one path, one loop
    • remove a bulb: all go out
    • more bulbs, same cell: dimmer
  • Parallel circuits
    • each bulb its own branch
    • remove a bulb: others stay lit
  • Conductors and insulators
    • copper conducts
    • plastic/rubber insulate
  • Safety
    • water conducts, avoid wet hands near sockets
Practise this topic →