What we will do today

1. What we will do today • Define the term ‘potential difference’. • Look at the ratio V/I for a resistor. • Define an equation relating resistance, voltage and current.

2. Potential difference • The ‘potential difference’ across a component in a circuit is the difference in voltage across that component. • It is measured in volts (V) using a voltmeter.

3. Voltage to Current ratio (READ) • What apparatus will be needed to investigate the ratio V/I for a series resistor circuit as the voltage is altered? • How will the ammeter be set up in the circuit? • How will the voltmeter be set up? • What will our circuit diagram look like?

4. Voltage to Current ratio:Circuit diagram

5. Voltage to Current ratio • Copy the following results table:

6. Voltage to Current ratio • We can now state that the ratio V/I for a resistor remains approximately constant for different currents. • Voltage and current are directly proportional

7. Relationship between V, I and R • Potential difference, current and resistance are all related through the following equation: • Potential difference = Current x Resistance V = IR • This is known as Ohm’s Law

8. What have we learned today? • The ‘potential difference’ across a component in a circuit is the difference in voltage across that component. • The ratio V/I for a resistor remains constant. • We can now state a relationship between voltage, current and resistance, V = IR

9. V = ? R = 10 Ω I = 0.5 A Example 1

10. V = 6 V R = ? I = 200 mA Example 2

11. V = 12 V R = 0.12 kΩ I = ? Example 3

12. 2003 Qu: 12

13. 2007 Qu: 8

14. 2007 Qu: 8