Electricity: Circuits and their Components: questions with answers

Both ends being metal is true of the cell's shape and says nothing about its terminals. The cap is the positive terminal and the flat disc the negative one, and the holder is built so that the negative terminal goes towards the spring side.

The cap of a cell is its positive terminal and the plain flat end its negative terminal, and cells are joined positive to negative. So the arrangement is right when the cap of one cell faces the flat end of the other. When it is not, turning one cell round is what fixes it. A wire and a metal strip do the same job; the strip is simply what a compartment uses.

The chapter defines a battery as two or more cells connected together. It then says the term battery is also used for a single cell, as for the one that powers a mobile phone. So that cell may be called a cell or a battery.

Current passes through an LED only when its positive terminal, the longer wire, is joined to the positive terminal of the battery. Here the longer wire runs to the end marked minus, so the LED is the wrong way round and no current passes. The circuit is complete, and the LED is sound: interchanging the two wires would light it.

An LED that stays dark one way round glows when the two wires to it are interchanged, because current can pass through it in one direction only. A complete circuit therefore does not by itself convict the component.

The glowing thin wire is called the filament of the lamp, and the filament is attached to two thicker wires that support it. The name belongs to the thin wire alone; the thicker wires are its supports and lead on to the lamp's two terminals.

A lamp glows only when both of its terminals are joined to the two terminals of the cell, so that current has a complete path to travel. Here the lamp's second stub and the cell's negative end are both free. Moving the one wire to the cell's other terminal would leave exactly the same gap.

With an incandescent lamp it does not matter which of its terminals connects to the positive or negative terminal of the cell. The lamp will glow as long as the circuit is complete and current flows through the filament. The one-way rule belongs to the LED.

When the lever touches the second contact it closes the gap and completes the path, so current flows and the lamp glows: the circuit is CLOSED. When the lever stands clear, the gap prevents current flow and the lamp does not glow: the circuit is OPEN. The two words run against their everyday sense, which is what makes them worth checking.

A single loop has no separately controllable parts: it is one path, and anything that breaks it anywhere stops the current everywhere in it. So moving the switch round the loop changes nothing about what it controls.

In the cell symbol, the long line is the positive terminal. The direction of current in a circuit is taken to be from the positive to the negative terminal. So the current is taken to leave by the side the long line is on, and to flow towards the marked point on that side.

A representation of an electrical circuit using symbols is called its circuit diagram. Symbols are the point of it: they make circuits easier to draw and to understand than pictures of the apparatus would be.

The plastic covering is an insulator, and current cannot pass through an insulator. The metal inside the wire is a conductor, but the current has to get into that metal at the join, and at the join it meets plastic. That is why about 1 cm of covering is removed from BOTH ends of each wire to expose the metal.

A circuit already known to work is the test: with everything else held fixed, whether the lamp glows depends on the one cell put in. Testing all six together gives one result for six questions, and a dark lamp would then say nothing about which cells were at fault.

Electricity is generated in multiple ways -- by windmills using wind energy, by solar panels, by falling water and by using natural gas or coal. The electric supply from these sources reaches our homes and factories via wires, and the socket is where that wiring ends. Nothing in the room makes the electricity; the room only receives it.