ELECTRICAL CIRCUITS In This Topic We Will Be Learning About: Components in a circuit. Circuit symbols. Current and the ammeter. Series and parallel circuits. Batteries and cells. Power in the circuit.

Which electrical component uses gaps in a circuit to stop ELECTRICAL CIRCUITS Electricity moves around electrical circuits. Electricity will only move around a complete circuit. If there are any gaps in the circuit, electricity will not flow. Which electrical component uses gaps in a circuit to stop electricity flowing? A switch

ELECTRICAL CIRCUITS Switches: These allow you to turn the electricity off by making a break in the circuit. You can also turn the electricity back on by moving the switch so the circuit is complete.

CIRCUIT SYMBOLS Which circuit symbols do you know? What does each of the symbols below represent?

CIRCUIT SYMBOLS - answers Switch. Cell. Battery of two cells. Connector. Battery. Bulb.

SWITCHES IN CIRCUITS Which of the bulbs in the circuits below are controlled by the switch? A B D C E F G H I J K

SWITCHES IN CIRCUITS answers The bulbs which are controlled by the switch in each circuit are shown in BLUE. C A B BOTH BOTH D E F I G H ALL FOUR J K ONLY I

CELLS What does a cell do? Cells supply electrical energy. This energy produces an electric current. When a bulb receives this energy in the form of the current, it converts the electrical energy into light and heat. The more energy the bulb gets, the hotter and brighter it will be. A battery is made up of more than one cell. The more cells it contains, the more powerful the battery is. The more powerful the battery, the bigger the electric current will be

POWER IN THE CELL The size of the electric current in a circuit depends on two things: The voltage of the battery. The higher the voltage of the battery, the larger the current. The components in the circuit. Adding components in series makes it more difficult for the electricity to flow, so this will make the current smaller. This is because the electricity has to flow through both bulbs. Adding components in parallel does not have the same effect.

SERIES CIRCUITS Series circuits: In a series circuit, the electricity has to go through all the components. You can think of the circuit as a bit like an obstacle course! The more obstacles there are, the smaller the electric current will be Adding bulbs in series gives the circuit more resistance. This means that adding bulbs in series will make the current smaller. This will then mean that each bulb gets dimmer. The current in a series circuit is the same size everywhere. Bulb is normal brightness. Bulbs are dim. Bulbs are very dim.

CELLS IN THE SERIES CIRCUIT Adding more cells to a circuit will provide more energy. This means the current will increase So the bulb will be brighter. Will the bulbs in the circuit below be normal, dim or bright? Bright Normal Very bright Normal

CELLS AND BATTERIES Cells and batteries have two ends or terminals: Which ends of the cells and batteries shown below are the positive terminals (+) ? C D A B E F G H A,D,E,H What is the other terminal called? The negative terminal (-).

BRIGHTNESS! How bright will the bulbs in the circuits below be? The first one is done for you. Normal

BRIGHTNESS ANSWERS Answers: Normal Normal Very bright Same number of bulbs and batteries. Same number of bulbs and batteries. More batteries than bulbs.

CHECK YOUR LEARNING Now try these:

CHECK YOUR LEARNING answers Normal Dim Off Same number of bulbs and batteries. Though there are the same number of bulbs and batteries, the two batteries are working against each other. More bulbs than batteries.

GOING AROUND THE CIRCUIT And these:

GOING AROUND THE CIRCUIT answers Dim Off Normal More bulbs than batteries. The two batteries are working against each other. Two of the batteries are working against each other. This leaves one battery to go with one bulb.

ELECTRICAL CIRCUITS Review: The current is the same size everywhere in a series circuit. This means that all the bulbs in series will light to the same brightness. The size of the current depends on the energy supplied by the battery and the resistance of the circuit. That is why both the bulbs in this series circuit light at normal brightness.

ELECTRICAL CIRCUITS Ammeters are used to measure current. Current is measured in amps (A). Ammeters are placed in series with the component. They then measure the current flowing through. A The ammeter in this circuit will measure the current flowing through both bulbs. Why can you place the ammeter anywhere in a series circuit? Because the current is the same size everywhere.

PARALLEL CIRCUITS Parallel circuits: X The current has only Parallel circuits have components in more than one loop. This means there is more than one pathway for the electricity to flow around. X The current has only one route to take. When the current gets to X, some goes along the green path and some goes along the blue path. This makes it easier for the current to flow. Current flows from + to -

ELECTRICAL CIRCUITS In a parallel circuit, the current does not have to get past all the “obstacles”. This means there is less resistance. The more different “branches” there are, the less resistance there is. This means that two or more bulbs in parallel with each other can both light at full brightness, or brighter than normal Very bright bright normal

CHECK YOUR LEARNING Why do series circuits and parallel circuits behave differently? Normal resistance – one bulb. The bulb lights normally. Double the resistance – two bulbs in series as “obstacles” to the current. The bulbs light dimly. The current can split up, so there is less resistance. The bulbs light brightly The headlights in a car are set up in a parallel circuit.

CHECK YOUR LEARNING How bright will these bulbs be? The first is done for you. normal

CHECK YOUR LEARNING- Answers bright normal Very bright normal normal Very bright Very bright bright normal bright dim dim