Example 1 · level 1
A 100 V supply is connected across a 20 Ω resistor. Find the current (in A).
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- I = 100 ÷ 20 = 5 A.
Answer: 5 A
CLASS 10 SCIENCE · ELECTRICITY
Ohm's law and electric charge
V = IR (volt = ampere × ohm). Charge Q = I × t (coulomb).
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Worked examples
Example 2 · level 2
A torch bulb draws 100 mA from a 9 V battery. Find the resistance of its filament (in ohm).
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- I = 100 mA = 0.1 A.
- R = 9 ÷ 0.1 = 90 Ω.
Answer: 90 ohm
Example 3 · level 3
An electric iron of resistance 30 Ω works on 120 V. How much charge (in C) flows through it in 60 s?
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- I = 4 A.
- Q = 4 × 60 = 240 C.
Answer: 240 C