2. 1 14.2 Electrical energy and voltage Warm-up Introduction Energy changes in a circuit Voltage Measuring voltage ? Voltage round a simple circuit Cells in series and parallel Check-point 2

3. 2 14.2 Electrical energy and voltage Warm-up A cell of a higher voltage means that the cell... functions longer. can supply higher power. releases more charge. gives a greater push to the charge flow. 1.5 V 3 V 9 V Others:_______________

4. 3 14.2 Electrical energy and voltage 0Introduction In a circuit... electrical energy  other forms of energy (e.g. heat and light) chemical energy  electrical energy energy transfer HOW?

5. 4 14.2 Electrical energy and voltage 0Introduction energy input energy output turning Like this?

6. 5 14.2 Electrical energy and voltage + – 1Energy changes in a circuit Battery drives free electrons to go round the circuit, from –ve terminal to +ve terminal. electrons gain energy from battery... the energy gained changes to heat and light electrons return to battery and gain energy again

7. 6 14.2 Electrical energy and voltage 1Energy changes in a circuit Simulation driving free electrons to go round

8. 7 14.2 Electrical energy and voltage 1Energy changes in a circuit 1 J is changed to heat and light when 1 C passes 3 J is changed to heat and light when 1 C passes electron flow the battery gives 4 J to 1 C of charge... E.g.

9. 8 14.2 Electrical energy and voltage 1Energy changes in a circuit Simulation Input = 4 J C -1 Output = 3 J C -1 Output = 1 J C -1

10. 9 14.2 Electrical energy and voltage 2Voltage Unit: volts (V), V = J C –1 Voltage = V = i.e. battery gives 4 J to 1 C of charge... 4 V 3 V 3 J is changed to heat and light when 1 C passes...

11. 10 14.2 Electrical energy and voltage e.g. 2 Energy change Question ? Example 2

12. 11 14.2 Electrical energy and voltage 3Measuring voltage Voltage across 2 points is measured by a voltmeter. leads to +ve pole of battery leads to –ve pole of battery + – V + – V + – V + – Simulation

13. 12 14.2 Electrical energy and voltage 4Voltage round a simple circuit Voltage across the battery V V V = sum of the voltages across components 1 V 1 V + 3 V = 4 V 3 V

14. 13 14.2 Electrical energy and voltage 5Cells in series and parallel This battery has cells connected in series. Each unit charge gains energy from each cell. 2 V total voltage = sum of the voltages of all cells 6  2 = 12 V

15. 14 14.2 Electrical energy and voltage 5Cells in series and parallel Cells connected in parallel... total voltage = voltage of 1 cell 2 V each unit charge passes through one cell only. The cells can last longer. 2 V

16. 15 14.2 Electrical energy and voltage Check-point 2 1If the battery has...If the battery has... 2How much energy...How much energy... 3The energy given to...The energy given to... 4The energy change...The energy change...

17. 16 14.2 Electrical energy and voltage Q1If the battery has... If the battery has delivered 12 J of energy to the bulb, how much charge has passed through the bulb? A1 CB4 C C6 CD12 C 3 V

18. 17 14.2 Electrical energy and voltage Q2How much energy is... How much energy is supplied to each coulomb of charge that flows through a 9-V battery? Voltage =  9 J is given to each coulomb of charge electrical energy charge

19. 18 14.2 Electrical energy and voltage Q3The energy given to... The energy given to ___ C of charge within the cell is called the electromotive force (e.m.f.) of a cell. Since it is measured in ______, it is also called voltage across a cell. 1 volts

20. 19 14.2 Electrical energy and voltage Q4The energy change... The energy change (to heat, light, sound, etc.) per coulomb of charge passing through an external circuit element (light bulb, buzzer, etc.) is called the potential difference across the circuit element. Since it is measured in ______, it is commonly called voltage across a circuit element. volts

21. 20 14.2 Electrical energy and voltage The End

22. 21 14.2 Electrical energy and voltage Example 2 Energy change The voltage across a lamp is 12 V. When a current of 2 A passes the lamp for 10 s, how much electrical energy is changed to heat and light energy? Charges passing the lamp Q = By E = QV = 20  12 = 240 J It 2  10 = 20 C

23. 22 14.2 Electrical energy and voltage Return