Presentation on theme: "Voltage and resistance in a circuit"— Presentation transcript:
1 Voltage and resistance in a circuit Level 1 Science
2 Voltage is the amount of energy carried by the charged electrons (current) in the circuit. Thus, the voltmeter measures the change in electron’s energy between entering and leaving a component so it has to be connected in parallel to that component.
3 An electrons voltage decreases as it goes through a component. The unit of voltage is the volt and the symbol is VAlessandro Volta
4 Power packs and batteries give electrons energy. This energy is all used up getting through the circuit until the electron gets back to the power pack or battery where it gets re-energised (or recharged).
5 For example:an electron comes out of a power pack with 12 volts of energy.It might use 11 volts getting through a light bulb and 1 volt getting through the wires.
6 The electron gets back to the power pack with no energy. The electron then gets 12 more volts of energy which it uses up as it goes around the circuit again.
7 Energy ConversionAn electron goes into a circuit component with some energy and comes out of it with less.Voltage measures how much energy an electron loses as it goes through a circuit component.
8 Circuit components are energy converters - they might convert electrical energy to : light if the component is a bulb, heat (heaters), sound (speakers), movement (motors), magnetism (solenoids).
9 Connecting voltmeters Voltmeters are also connected across components red terminal to red terminal in parallel. (Touch test)
10 Energy of electronsWhen electrons leave their power source, they have a certain amount of energy. They lose all their energy as they pass through components and they must return to the power source with 0 Volts.
11 SERIESVoltages across each component ADDS to total voltage
18 Conductors have a very low resistance. Resistance is a property of a substance that limits the flow of electrons through it.Conductors have a very low resistance.Insulators have a very high resistance.
20 Resistance enables a component to convert electrical energy to another form of energy. ie - heating coils convert electrical E to heat E- lamp filaments convert electrical E to heat E and then to light E.
21 - electrical motors convert elec E to magnetic E to get kinetic E. Resistance can be an advantage if we wish to create heat (as in a toaster) or it can be a disadvantage if we don’t want to create heat (as in an electric motor).
22 Limiting heat loss in a circuit: - a short length of wire has less resistance than a long length of wire.- a good conductor has less resistance than a poor conductor.
23 R = -a low current creates less resistance than a high current. Resistance is calculated by:R =VI
24 Where R = resistance measured in ohms (), V = voltage measured in volts (V),I = current measured in amps (A).
25 Temperature and Resistance When the temperature of a conductor is kept constant, its’ resistance stays constant = Ohms LawAs the temperature of a conductor increases, so does its resistance.
26 PowerIs a measure of how quickly electrical energy is converted into other forms of energy.Power is measured in watts (W).1W is equal to 1 joule per second.
27 Power = Voltage X Current P = V I Where P is measured in watts (W), Power CalculationsPower = Voltage X CurrentP = V IWhere P is measured in watts (W),V is measured in volts, andI is measured in amps
28 Electricity at HomeMains power is 240V AC.AC means the current changes direction 50 times per second and is said to be 50 Hertz (50 Hz).Fuses are used to protect people and property. They melt when the current gets too high.
29 3 Pin PlugsNeutralBluePhaseRedEarthYellow and Green
30 Current flows from phase to neutral. The Earth wire is a safety wire to protect people from any short circuit.