Next Page: Voltage and Current
Also see: Circuit Symbols and Circuit Diagrams
In seriesso that each component has the same current.The battery voltage is divided between the two lamps
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In parallelso that each component has the same voltage.Both lamps have the full battery voltage across them.
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For example: the circuit on the right shows a resistor and LED connected in series (on the right) and two lamps connected in parallel (in the centre). The switch is connected in series with the two lamps.
See Lamps in Parallel below for another example.
Normally you would expect all the lamps to go out if one blew, but Christmas tree lamps are special! They are designed to short circuit (conduct like a wire link) when they blow, so the circuit is not broken and the other lamps remain lit, making it easier to locate the faulty lamp. Sets also include one 'fuse' lamp which blows normally.
If there are 20 lamps and the mains electricity voltage is 240V, each lamp must be suitable for a 12V supply because the 240V is divided equally between the 20 lamps: 240V ÷ 20 = 12V.
WARNING! The Christmas tree lamps may seem safe because they use only 12V but they are connected to the mains supply which can be lethal. Always unplug from the mains before changing lamps. The voltage across the holder of a missing lamp is the full 240V of the mains supply! (Yes, it really is!)
This type of circuit is often called a parallel circuit but you can see that it is
not really so simple - the switches are in series with the lamps, and it is these
switch and lamp pairs that are connected in parallel.
The diagram shows a simple circuit with two switches connected in series to control a lamp.
Switch S1 AND Switch S2 must be closed to light the lamp.
The diagram shows a simple circuit with two switches connected in parallel to control a lamp.
Switch S1 OR Switch S2 (or both of them) must be closed to light the lamp.