Electricity Revision Electricity circuit symbols Name each of

Electricity Revision

Electricity – circuit symbols Name each of the circuit symbols 1 9 2 10 3 11 4 12 5 13 6 7 8 14

DEMONSTRATE Draw each of the circuits shown as circuit diagrams using the correct symbols and name each of the circuits shown

ANSWERS

Electrical current • It is measured in amps (A) • Using an ammeter • This is the symbol for an ammeter • An ammeter is connected to the circuit in series with the other components

Current in series and parallel circuits • What happens to the current in each type of circuit?

Potential difference • The potential difference between two points in an electric circuit is the work done when a coulomb of charge passes between the points. • I. E. Voltage is energy per unit of charge • It is measured in volts (V) • Using a voltmeter • This is the symbol for an voltmeter • A voltmeter is connected to the circuit in parallel with the other components

Potential difference in series and parallel circuits • What happens to the potential difference in each type of circuit?

DEMONSTRATE • What is the potential difference across each bulb in each of the circuits shown?

ANSWERS • What is the potential difference across each bulb in each of the circuits shown? 115 V each 230 V each

Resistance • Resistance is the opposition that a substance offers to the flow of electric current. • It is measured in ohms (Ω) • It can be calculated when you have the current and voltage

Resistance in series and parallel circuits 4 2 Total resistance of 9Ω Total resistance of 1. 33Ω Adding resistors in series means the current has to go through more resistors so increases total resistance and reduces total current Adding resistors in parallel provides extra paths for the current so reduces total resistance and increases total current

Resistance required practical • How could you find out how the length of a wire affects the resistance?

• Sellotape a length of thin nichrome wire or constantan wire along the length of a metre ruler, alongside the cm scale. • Use crocodile clips to connect the wire into the circuit as shown, using the crocodile clips to select different lengths of the wire at 10 cm intervals starting at the full 100 cm. • For each different length, from 100 cm to 30 cm, take a voltmeter and ammeter reading then work out the resistance of the wire Care Use a low voltage or the wire will get hot, affecting the results and creating a hazard V I R

Resistance required practical

Resistors required practical How could you find out how different components affect the resistance of a circuit? You must know this standard test circuit

• Set up the circuit as shown, including a variable resistor (which might be built into your power supply as a controller on the front) to vary the potential difference. • For 4 or more values of potential difference measure the current through the bulb. Swap the connectors to the power-supply to obtain readings for negative p. d and current. • Repeat for a resistor and a diode to get current and p. d values for them.

Learn these graphs and what they mean Ohmic conductor/resistor Filament Lamp Diode

Two more resistors and their graphs: Thermistor LDR

Direct and alternative current

Direct current • If the current flows in only one direction it is called direct current, or d. c. • Batteries and cells supply d. c. electricity, with a typical battery supplying maybe 1. 5 V.

Alternative current • If the current constantly changes direction, it is called alternating current, or ac and is caused by an alternating potential difference • Mains electricity is an ac supply, with the UK mains supply being about 230 V. It has a frequency of 50 Hz (50 hertz), which means it changes direction, and back again, 50 times a second.

Plugs Earth wire – Green 1 and yellow 2 Fuse What are the wire colours and their jobs? Neutral wire 5 - blue Live wire 3 - Brown 4 grip Cable

Electricity equations Q I T

Electricity equations V I R

Electricity equations P V I P I 2 R Equation given on physics equation sheet

Electricity equations E P T

Electricity equations E V Q

Electricity units Current Time Potential difference Charge Resistance Power Energy Amps 1 (A) 2 Seconds (S) Volts 3(V) 4 Coulombs (C) Ohms 5 (Ω) Watts 6 (W) 7 (J) Joules

The national grid There are 3 parts to the national grid, can you name them? 2 1 3

Transformers • Step-up transformers at power stations produce the very high voltages needed to transmit electricity through the National Grid power lines. • This is because high voltages improve efficiency by reducing heat loss in the power lines. • But high voltages are too dangerous for use in the home, so step-down transformers are used locally to reduce the voltage to safe levels.

DEMONSTRATE • Explain why a step-up transformer is used at a power station.

ANSWERS • Explain why a step-up transformer is used at a power station. The potential difference (voltage) is increased So the current decreases This reduces energy / power loss (in cables) And improves the efficiency

Static electricity Triple

DEMONSTRATE

ANSWERS • Electrons are transferred from the cloth to the rod