Example 1 · level 1
Resistors of 17 Ω, 10 Ω, 9 Ω are connected in series. Find the equivalent resistance (in ohm).
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- R = 17 + 10 + 9 = 36 Ω.
Answer: 36 ohm
CLASS 10 SCIENCE · ELECTRICITY
Resistors in series and parallel
Series: R = R₁ + R₂ + … (same current). Parallel: 1/R = 1/R₁ + 1/R₂ + … (same voltage); for two, R = R₁R₂/(R₁ + R₂).
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Worked examples
Example 2 · level 2
4 identical bulbs of 120 Ω each are connected in parallel in a wedding light string. Find the equivalent resistance (in ohm, correct to 2 decimal places).
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- 1/R = 4/120, so R = 120/4 = 30 Ω.
Answer: 30 ohm
Example 3 · level 3
A 7 Ω resistor is in series with a parallel pair of 4 Ω and 12 Ω. The combination is connected to a 24 V battery. Find the current drawn from the battery (in A, correct to 2 decimal places).
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- Parallel part = 3 Ω.
- Total = 7 + 3 = 10 Ω.
- I = 24 ÷ 10 = 2.4 A.
Answer: 2.4 A