Current Flow (3b4,3b5,3b6)

 

A Battery provides an almost constant voltage, but current will only flow if there is a circuit (route) for the electrons to flow out of the battery, through the various wires and components such as resistors and lamps back to the battery.

 

With a battery, current flow in one direction only.

 

 

 

 

 

 

 

 

 

 

 

 

For some components such as light bulbs, it does not matter in which direction the electrons flow, the light still lights up if they are flowing in either direction, so a simple circuit where  a battery is connected to a light bulb will work no matter whether the positive (+) terminal and negative (-) terminals of the battery are swapped around.

 

In fact for a light bulb, it is so unimportant which way round it is connected, that it will also work with AC

 

 

 

·     For most DC ‘electronic’ circuits (e.g. radios, transmitters, cameras, portable CDs and mini disc players, mobile phones, portable computers etc.) if you connect the battery round the wrong way you are likely to badly damage the equipment.  So don’t guess – always check that you are connecting batteries the correct way round! 

 

·     Many of these DC ‘electronic’ pieces of equipment can only be connected to the AC mains if using a step down transformer and rectifier to convert the 230 AC mains to 12V DC.

 

Direct Current (DC) and Alternating Current (AC)

There are two types of electricity, Direct Current (DC) and Alternating Current (AC).  The graph on the right illustrates these two types.

Direct Current (DC)

Direct Current known as DC is a virtually constant voltage that does not change with time, and does not change direction (see green line on graph which shows 5 Volts DC).

 

Batteries supply Direct Current.

Alternating Current (AC)

Alternating Current known as AC reverses its direction several/many times per second (see blue line on graph to the right).

 

Notice how part of the time the Voltage is positive, part of the time the Voltage is negative.

 

The graph below illustrates how the voltage changes with time.

 

 

Dynamos provide alternating current.

 

Apart from batteries, it is generally easier to generate alternating current than Direct Current.

 

 

Next