S.MORRIS 2006 Currents CIRCUITS More free powerpoints at

2 types of electric currents AC = Alternating current Electrons in the circuit move in 1 direction for some time and then switch directions and go the opposite way Ex: household outlets and appliances DC = Direct current Charges always flow in the same direction From negative to positive Ex: batteries

The CELL – the power source Cells are a type of voltage source that converts chemical energy into electrical energy when a circuit is connected. When two or more cells are connected together we call this a Battery.

What is an electric circuit? Any pathway through which electrons can flow/travel + - The bare essentials for a circuit: battery/power source Load (lightbulb/lamp) Wires

One more piece… Most circuits also have a switch that is used to turn the circuit on and off when the switch is open, it creates a gap so that electrons cannot flow when the switch is closed, the circuit is complete and electrons can move through it

types of circuit There are two types of electrical circuits; SERIES CIRCUITSPARALLEL CIRCUITS

The components are connected end-to-end, one after the other. They make a simple loop for the current to flow round. A break anywhere in the loop will result in an open circuit and no more moving electrons SERIES CIRCUITS If one bulb ‘blows’ it breaks the whole circuit and all the bulbs go out.

PARALLEL CIRCUITS The current has a choice of routes. If there is a break in one path, it might not effect the other path The components are connected side by side.

circuit diagram cellswitchlampwires Scientists usually draw electric circuits using symbols;

measuring current Electric current is measured in amps (A) using an ammeter which is connected in series in the circuit. A

measuring current A A This is how we draw an ammeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT

measuring current SERIES CIRCUIT PARALLEL CIRCUIT current is the same at all points in the circuit. 2A current is shared between the components 2A 1A

Discuss with your neighbor what the missing ammeter readings would be ? ? 4A 3A? ? 1A ? 3A 1A

measuring voltage The ‘electrical push’ which the cell gives to the current is called the voltage. It is measured in volts (V) on a voltmeter which is drawn across (on top of) circuit components V

V measuring voltage V V V This is how we draw a voltmeter in a circuit. SERIES CIRCUIT PARALLEL CIRCUIT

series circuit 1.5V voltage is shared between the components 1.5V 3V

voltage is the same in all parts of the circuit. 3V parallel circuit 3V

Let’s recap: Series Circuit Parallel Circuit Current Voltage

measuring current & voltage copy the following circuits on the next two slides. complete the missing current and voltage readings. remember the rules for current and voltage in series and parallel circuits.

measuring current & voltage V V 6V 4A A A a)

measuring current & voltage V V 6V 4A A A A b)

answers 3V 6V 4A 6V 4A 2A 4A a)b)

measuring resistance in series In series: to find total resistance of a series circuit, add the individual resistances of the objects in series The total resistance of this circuit would be 5 Ω 6V 3 Ω2 Ω

What happens to voltage as you move past each light? -It drops – we can calculate the “voltage drop” of each light using Ohm’s law 6V 3 Ω2 Ω

measuring resistance in parallel In parallel, use the following formula to find the total resistance: R T = R 1 x R 2 = R 1 + R 2 Total resistance in parallel will always be less than the smallest resistor 3 Ω 2 Ω 6V