Simple Electric Circuits D. Crowley, 2008

Simple Electric Circuits Thursday, April 20, 2017 Simple Electric Circuits To be able to draw simple electric circuits and know what happens when more bulbs are added

Electricity What is electricity? Electricity is the flow of electrical power (charge) in the form of electrons Electricity is a useful secondary energy source – most energy sources (like coal, oil, nuclear, wind etc…) can be converted into electricity Electricity is the flow of electrons around our electrical circuit

Circuits low pressure high pressure boiler and pump radiator radiator An electric circuit is like the central heating system in a house… low pressure high pressure There is a pump which pushes water all around the house The water everywhere starts to move at the same time There are pipes which carry the water In the pipes the water is flowing When river water moves, we say that a current of water flows - when electric charges move in a wire, we say that an electric current flows boiler and pump radiator radiator flow of water

Circuits A bulb in the circuit is like a radiator – an electrical device uses electrical energy, supplied by the circuit The wires are like pipes - they carry the flow of electricity (current) around the circuit (flow of electrons goes from negative to positive) The electrical current is pushed by the cell (battery) – this is the voltage Cell + - Wires Lamp

Electric Circuits An electric current needs two things: - Something to make the electricity flow (e.g. a battery or power pack) A complete circuit Without these two basic things, an electric current will not flow Cell + - Wires forming a complete circuit

Component Diagrams Circuit symbols are used to show the components in an electrical circuit (wires are represented by straight lines) Current – the flow of electricity (flow of electrons) around the circuit Voltage – the driving force which pushes the current around the circuit Resistance – anything in the circuit which slows the flow down

Component Symbols A common list of components is shown below – use this to complete the simple electric circuits worksheet

Simple Electric Circuits

Simple Electric Circuits

Switches Switches are used to control components in circuits In a simple circuit with one switch, the switch controls all the components…

Series & Parallel There are two types of circuit – series and parallel For now, we will concentrate on series circuits – circuits where all the components are connected in a line, end to end Removing one component breaks the circuit, stopping all the components Christmas tree lights are often in series, so when one bulb blows, they all stop They are also used for warning systems, so if a component breaks the light in series will stop, hopefully alerting you

Current What is current? Current is a measure of how much electric charge flows through a circuit (the flow of electrons around a circuit, from negative to positive terminals)) Current is measured in amps – e.g. 20A current is bigger than 5A current To measure current in a circuit, the ammeter must be placed in series – it does not matter in what order you place this

The ammeter can be placed after the components (lamp) Current To measure the current, the ammeter must be placed in series (in any order) + - Ammeter A The ammeter can be placed after the components (lamp)

Or the ammeter can be placed before the component (bulb) Current To measure the current, the ammeter must be placed in series (in any order) + - Ammeter A Or the ammeter can be placed before the component (bulb)

Experiment

Experimental Observations Your first experiment is to find out what happens to the brightness of bulbs when you add more than one to a circuit Firstly set up a circuit with one bulb in it, and note how bright it is – place the ammeter in different parts of the circuit, testing the current + - + - A A

Experimental Observations Secondly add a second bulb to the circuit and repeat the current test (place it in different positions Then repeat this with three bulbs in the circuit + - + - + - A A A

Experimental Observations Experiment with three bulbs in the circuit + - A + - + - + - A A A

Ammeter Your second experiment is to find the current of each circuit Reset your circuit to contain just one bulb, and connect the ammeter in series and record the amps reading Then repeat this with two and three bulbs, recording each current reading + - + - + - 1. 2. 3. A A A

Current The current is not used up by the components in a circuit The current is the same anywhere in a series circuit + - Current is the same, anywhere in the circuit A A Current is the same at this point in the circuit, e.g. 1A Current is the same at this point in the circuit, e.g. 1A

Current is always 1A, anywhere in this circuit Dimmer Bulbs As more bulbs are added to the circuit they all get dimmer As more bulbs are added the resistance increases, reducing the flow of current Having a circuit with many bulbs in it causes a low current, but remember the current is still the same anywhere in this circuit + - + - Current is always 1A, anywhere in this circuit Current is reduced in this circuit (more resistance) but it is still always 0.5A, anywhere in this circuit A A

Key words: same / decreased / same / not Current Summary Circuit 1 Circuit 2 A A A A A Key words: same / decreased / same / not Circuit 1 – the current at different positions in the circuit, before and after the lamp was the __________ Current is __________ used by the components in the circuit Circuit 2 – increasing the number of components in the circuit __________ the current The current at all points in a series circuit is __________ same not decreased same