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.

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.

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?

Voltage to Current ratio: Circuit diagram

Voltage to Current ratio Copy the following results table: Potential difference across resistor (V) Current through resistor (mA) Ratio V/I

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

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

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

Example 1 V = ? R = 10 Ω I = 0.5 A

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

Example 3 V = 12 V R = 0.12 kΩ I = ?

2003 Qu: 12

2007 Qu: 8