MadSci Network: Physics
Query:

Re: How does wiring batteries in series make light bulbs brighter?

Date: Tue Mar 14 02:35:16 2000
Posted By: Ewen McLaughlin, Lecturer, Chemistry, Swansea College
Area of science: Physics
ID: 952372008.Ph
Message:

There are two things to understand about electricity: current and voltage (properly called electromotive force).

There are no everyday situations that are quite like electricity, but one that is similar enough is the chain of a bicycle. I hope you know your bicycles!

The similarities are like this: energy is transfered from the battery (pedals) to the bulb (wheel) by a circuit (chain).

You can measure how fast the electricity is flowing (current), or the speed of the chain in the case of a bike. You can also measure the voltage, which in bike chain terms is the tension on the chain.

Imagine you are coasting on your bike. The chain is slack (no voltage) and it is not moving (no current) - no energy is being transfered.

If you pedal and the going is easy, you don't need much force to pedal quickly. This is like a low resistance circuit where small voltages produce large currents.

Pedalling uphill is harder, so you apply more force, tensing the chain and sending more energy to the wheel. The wheel does not always go faster when you pedal harder, but more energy is transfered.

In chain terms, the power passed to the back wheel is the force on the chain multiplied by the speed of the chain. In an electric circuit, the power passed from battery to bulb is current times voltage.

An increase in current is due to a) more electrons flowing and b) electrons flowing faster. Current is a combination of these two factors.

The energy transfer at the bulb is due to the bulb resisting the flow of current. Electrons find it hard to pass through the bulb and lose energy. This energy is what heats up the bulb. The effect is like friction. The voltage keeps pushing the current round the circuit, so energy is constantly transfered to the bulb.

As with friction, you will transfer energy if you have to push electrons through the bulb with great force (high voltage) or if you push a great many electrons through (high current). In friction terms, this is like rubbing harder or rubbing more quickly.

Sorry for the long answer! Electricity's difficult!


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