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Ohm's lawThree quantities. Know any two, and you can find the third.
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I = V ÷ R
amps = volts ÷ ohms
Tap V, I or R on the triangle to cover it.
The three forms
V = I × R volts = amps × ohms I = V ÷ R amps = volts ÷ ohms R = V ÷ I ohms = volts ÷ amps
There's no formula sheet in the exam. You can ask for blank paper, but it stays in the room. Write the three formulas out until you know them by heart.
Example 1: find the current
Supply 230 V, heating element resistance 6 Ω I = V ÷ R = 230 ÷ 6 = 38.33 A
Example 2: find the resistance
Supply 230 V, current measured 12 A R = V ÷ I = 230 ÷ 12 = 19.17 Ω
If 230 ÷ 6 comes up as a fraction (115/3), press the S⇔D button to switch it to a decimal. On other calculators, look for a FORMAT or decimal setting. Get used to your own calculator, because that's the one you'll take into the exam.
A 6 A lighting circuit doesn't mean the lights draw 6 A. They might only draw 2.5 A. The 6 A breaker is sized to protect the cable.
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