Download V = IR

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)
0.5
1.0
1.5
2.0
2.5
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
2007 Qu: 8