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# 5.8 current and pd in a circuit

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### 5.8 current and pd in a circuit

1. 1. The circuit has two components in series. Each component has a different resistance. <ul><li>1 What is the p.d. of V? </li></ul><ul><li>2 What do the values tell you about the resistance of the buzzer compared to the resistance of the resistor? </li></ul><ul><li>HINT: R = V/I. What do you know about the current in the resistor and the buzzer? </li></ul>5.8 Current and p.d. in a circuit February 16, 2011
2. 2. Answer <ul><li>1 1 V </li></ul><ul><li>2 The resistance of the resistor is much less than the resistance of the buzzer. (This follows as current is the same through both and R = V/ I so lower V means lower R . Alternatively, argue that the larger resistance requires a greater p.d. to make the current flow through it.) </li></ul>
3. 3. Learning objectives <ul><li>Show that current can be calculated using V=IR </li></ul><ul><li>Revise that electrical energy can be transferred in electrical appliances </li></ul><ul><li>Show that electrical items have a plate with information including the supply voltage and power rating and sometimes the current </li></ul>
4. 4. Can you do these? <ul><li>3 Use V=IR to calculate the pd of V 1 </li></ul><ul><li>4 Use V=IR to calculate the pd of V 2 </li></ul><ul><li>5 Use V=IR to calculate V 3 </li></ul><ul><li>6 Use R=V/I to calculate R of the motor </li></ul>
5. 5. Answers <ul><li>3 = 1.2 V </li></ul><ul><li>4 = 4.8 V </li></ul><ul><li>5 = 3 V </li></ul><ul><li>6 = 10 Ω </li></ul>
6. 6. Series and parallel (current) <ul><li>For series: </li></ul><ul><li>For parallel: </li></ul>
7. 7. Series and parallel (voltage) <ul><li>For series: </li></ul><ul><li>For parallel: </li></ul>
8. 9. Energy transfers
9. 10. Kettle Electrical energy Heat Sound
10. 11. Television Electrical energy Heat Sound Light
11. 12. Light bulb Electrical energy Heat Light
12. 13. Motor Electrical energy Kinetic Sound
13. 14. Power rating plates