Lesson 4: electric current

Objectives: 1. Describe how energy in a circuit is transferred by current, which has the unit of amperes (A)2. Describe current in series and parallel circuits

What is electricity?

1. What does “current” mean?

Current: The flow of electrons. Electrons can be thought of as negatively charged "particles".

• To save money, you decide to build what you think is a waterfall. It looks like this. ..

Unfortunately the water doesn't flow at all. You cannot understand why.For water to flow, there needs to be a difference in energy between one area and another. (example height)

As you admire your waterfall and show it off to your friends, you suddenly discover that it has stopped flowing! The reason is that the higher water tank is now empty

For the same reason, if you simply connected a pipe from the lower tank to the upper tank, the water won't go back to the higher tank

For this, we need to provide energy to the system. This is done with the water pump. Now finally we have a beautifully working continuous waterfall

Instead of having a waterfall, let us imagine that we want to light up a light bulb. A light bulb is something that lights up when current passes through it.

Since the electrons in the wire are all not flowing in a particular direction, there is no current passing through the bulb, and hence the bulb does not light up.

• Just like the water in the waterfall, electrical circuits need a potential energy difference to make the current flow.

• The next image shows two wires. The upper wire has no potential difference across it. The electrons are randomly moving in all directions with no net flow. Therefore this wire is not carrying any current.

• The lower wire has a potential difference across A and B. It makes the electrons flow in a particular direction and therefore this wire is carrying a current.

Potential difference sources have a ' negative pole' and a 'positive pole'. Current leaves the negative pole and returns to the positive pole.

Ammeter

Reads the current at any point in a circuit

In partners 1. Create a series circuit. Add in the ammeter as the paper tells you. Record the amount. Record your observations in a chart.2. Repeat the above instructions in a parallel circuit. 3. Write a conclusion.

Current is not used up in a circuit.

Series circuit: the readings are the same no matter where you measure it in a series circuit.

Parallel circuit: current is split, and rejoins, at the junctions in a parallel circuit.

Summary

Current is not used up in a circuit.

Series circuit: -The current goes down each time an extra bulb is added-The readings are the same no matter where you measure it in a series circuit.

Parallel circuit: - Extra current is drawn from the power supply each time a bulb is added- The current is split and rejoins at the junctions in a parallel circuit.