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Published byMargaret Shields Modified over 9 years ago
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Today we are going to look at:
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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 “Ohm’s” ( ) “A measure of how much voltage is required to let a current flow”
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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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“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 IR This gives us the formula’s V = I x R V I = R V R = I
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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 V IR Step 2: Select correct equation V = I x R
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Step 3: Plug in the numbers V = ?I = 2A& R = 12 Step 4: Calculate V = 2 x 12 Step 5: Solution V = 24V Don’t Forget the units!
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Now you try one! Q: The resistance of a circuit is 15 and the current is 3A. What is the voltage?
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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 V IR Step 2: Select correct equation V I = R
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Step 3: Plug in the numbers V = 25VI = ?R = 5 Step 4: Calculate I = 25 5 Step 5: Solution I = 5A Don’t 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 V IR Step 2: Select correct equation V R = I
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Step 3: Plug in the numbers V = 300VI = 2AR = ? Step 4: Calculate R = 300 2 Step 5: Solution R = 150 Don’t 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?
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