We began by studying how fluids flow, because there are many analogies between this and electrical circuits. We defined the flow rate of a fluid to be the amount of fluid that is delivered, divided by how long it took to deliver it. Fluids flow downhill because this lowers their potential energy: a height difference between two ends of a pipe gives rise to a pressure difference that makes the fluid go. The flow rate is also affected by the size of the pipe or tube carrying the fluid. The electrical equivalents to these are the electrical current (measured in amperes); the current flows because there is a potential difference (measured in volts); and the size of the current is affected by the resistance of the wire.

As an interesting special case we studied siphons. Here some fluid is moving upwards but this is allowed because elsewhere fluid is flowing downwards, and the potential energy of the whole system is decreasing.

The electrical quantity that is analogous to the flow rate of a fluid is the electrical current, which is measured in Amperes. The analog of pressure is voltage. Electrical current stays inside conductors (such as wires). In order for an electrical device to work there has to be a path for the current: a circuit. Some electrical devices only work when the current flows the right way. We also studied complex circuits, in which all of the current might pass through several different devices in sequence (when they are in series), or in which the current divides and some goes through each device (when they are in parallel).

A circuit delivers energy to a device in a circuit. The power (energy per unit time) is the product of the current through the device and the voltage difference across it (Watts = Volts x Amperes).

In many circuit elements, the current is proportional to the voltage difference, so that Voltage = Current x Resistance.

A high dam provides water pressure. When water flows through the turbine, energy is converted into mechanical form (motion). The amount of power released depends on the pressure and the flow rate	spacer	A battery provides electrical potential (voltage). When current flows through the motor, energy is converted into mechanical form (motion). The amount of power released depends on the voltage and the current

In some respects electricity is safer than other ways to deliver energy, but we must be respectful of it, since we can't see or hear or smell an electrical hazard. The current required to deliver a lethal shock is very small. The basic rule is to avoid becoming part of an electrical circuit that would send current through the chest area.

The space around a magnet contains a field, that tells a compass needle which way to point, and causes forces on other magnets, iron and steel objects, and current- carrying wires. The parts of a magnet where the field emerges is called the N pole, and where the field enters the magnet is called the S pole. Magnets always have both N and S poles.

It takes energy to make a magnetic field. We can use this idea to explain the magnetic force.

When we turn off the current to an electromagnet, the magnetic energy will keep the current going briefly, and in the process may give rise to an unusually high voltage in the circuit or even a voltage in a different circuit.

We found that there are materials that are themselves magnetic (permanent magnets), and materials that only become magnetic in the presence of other magnets. We can also produce a magnetic effect with a current carrying wire.

Electricity is related to magnetism in several ways. A current causes a magnetic field, and a magnetic field causes a force on a current. A rapidly changing magnetic field gives rise to an electrical effect that will make currents flow.

We have studied several electrical components:

• Wires and conductors. If we wish to deliver a lot of power, we must use wires that are very good conductors.
• Resistors. These are elements that conduct, but not very well. They limit the current. Resistance is also the mechanism whereby electrical energy is converted into heat.
• Incandescent light bulbs. These are really just resistors. But they deliver power to a tiny wire that gets so hot that it glows.
• Switches. By connecting and disconnecting parts of a circuit, we can affect which parts are working.
• Batteries. These are devices for converting chemical energy into electrical energy.
• Light emitting diode. This is a kind of transistor, which turns electrical energy directly into light without having to make something hot. Because they are more efficient (and less bright) than the incandescent light bulb, they require less current to operate.
• Capacitor. This is a device for storing electrical energy. They can't hold as much energy as a battery of similar size, but the are rechargeable indefinitely.
• Electromagnet. A current gives rise to a magnetic field, which we can make bigger by making a coil and by wrapping it around a steel or iron object.
• Buzzer. The kind we have in our kit combines an electromagnet with a circuit to turn the magnet on and off. It is one of several ways to make sound using an electrical signal.
• Motor. By turning a magnet on and off, we can provide an alternating force that will make a rotor go around.