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# 2.9 understanding electricity

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### 2.9 understanding electricity

1. 1. 2.9 Understanding electricity December 7, 2010
2. 2. Key terms <ul><li>Series : in a series circuit the components are connected in a line, end to end, so that the current flows through all of them one after another </li></ul><ul><li>Parallel: in a parallel circuit the components are in separate paths and the current is split between the two paths </li></ul>
3. 6. What is electricity? <ul><li>Electricity is the flow of electric charge </li></ul><ul><li>This charge could be positive and negative ions in your phone or negative electrons in your PS3 </li></ul><ul><li>When charge flows there is a current </li></ul><ul><li>Electrical energy allows a current to flow in a circuit </li></ul><ul><li>A measure of the energy carried between two points in a circuit is called voltage (or potential difference) </li></ul>
4. 8. Measuring electricity <ul><li>We use a voltmeter to measure voltage and an ammeter to measure current </li></ul><ul><li>The way we connect them is important </li></ul><ul><li>A voltmeter is always connected in parallel </li></ul><ul><li>An ammeter is always connected in series </li></ul>
5. 9. Series
6. 10. Parallel
7. 11. Case study: fault finder <ul><li>Sophia is a technician at an electronics company. Today she is repairing a DVD player that seems to have no power. She wants to measure the voltage and find out if there is a break in the circuit. </li></ul><ul><li>How could she do this? </li></ul>
8. 12. Ohms Law Voltage equals the product of the current and the resistance
9. 13. Resistors <ul><li>You can use an ammeter and a voltmeter to check the values you calculate for a circuit using Ohm’s law </li></ul><ul><li>High levels of current can be dangerous, in the lab we only use low levels such as mA (milliamps) or even μ A (microamps) </li></ul><ul><li>All electrical devices have resistors which limit the current that flows through a component so they are not damaged </li></ul>
10. 14. Worked example <ul><li>What is the voltage across a 300 Ω resistor if the current flowing is 0.01 A? </li></ul>
11. 15. Worked example <ul><li>If the voltage across the resistor was 9 V what current would be flowing? </li></ul>
12. 16. Units and symbols Resistance Current Voltage Symbol Unit Electrical property
13. 17. Units and symbols Ω Ohm Resistance A Ampere (Amp) Current V Volt Voltage Symbol Unit Electrical property
14. 18. Activity 1 <ul><li>What meter is used to measure current? </li></ul><ul><li>How should it be connected in order to measure current? </li></ul><ul><li>Draw a diagram to show this </li></ul>
15. 19. Activity 2 <ul><li>You are an electrician. Part of your work is to make sure electrical circuits are working correctly. To do this you must understand Ohm’s law and how to use measuring instruments </li></ul><ul><ul><li>Draw the symbols for a voltmeter and an ammeter </li></ul></ul><ul><ul><li>If a resistor in a circuit is 1500 Ω , what is the current if it is connected to a 1.5 V supply? </li></ul></ul><ul><ul><li>Using a circuit diagram, show how you could confirm the current and voltage readings in question 2 by using the correct measuring instruments </li></ul></ul>
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