Relationship Voltage,

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Unit 4 Relationship Voltage, Current Resistance
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Today we are going to look at
"Ohm's Law"
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Revision Current, Voltage Resistance
Current Measured in Amperes or Amps (A) The
rate of flow of electrons through a
circuit Voltage Measured in Volts (V) Used
to drive the electrons through the
components Resistance Measured in Ohms (?
) A measure of how much voltage is required to
let a current flow
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History
Georg Simon Ohm (1787-1854) Ohm formulated the
relationship between voltage, current
resistance as follows.
The current in a circuit is directly
proportional to the applied voltage and inversely
proportional to the resistance of the circuit
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Ohm's Law
V I x R
Voltage (V) is equal to the current (I)
multiplied by the resistance (R)
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If we use a triangle to help us, then we can
arrange the formula to make it easier to use.
V
I
R
This gives us the formulas
V I x R
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Example 1 Voltage
Q The resistance of a circuit is 12? and the
current is 2A. What is the voltage?
Step 1 Draw Triangle
Step 2 Select correct equation
V I x R
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Step 3 Plug in the numbers
Step 4 Calculate
V ? I 2A R 12?
V 2 x 12
Step 5 Solution
V 24V
Dont Forget the units!
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Example 2 Current
Q The voltage supply is 25V and the resistance
is 5 ?. What is the current
Step 1 Draw Triangle
Step 2 Select correct equation
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Step 3 Plug in the numbers
Step 4 Calculate
I 25 ? 5
V 25V I ? R 5?
Step 5 Solution
I 5A
Dont Forget the units!
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Now you try one!
Q The voltage supply is 40V and the resistance
is 10?. What is the current?
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Example 3 Resistance
Q The voltage supply is 300V and the current is
2A. What is the resistance?
Step 1 Draw Triangle
Step 2 Select correct equation
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Step 3 Plug in the numbers
Step 4 Calculate
R 300 ? 2
V 300V I 2A R ?
Step 5 Solution
R 150 ?
Dont Forget the units!
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Now you try one!
Q The voltage supply is 500V and the current is
50A. What is the resistance?