Circuit and electromagnetism basics
What is the combined resistance of three resistors, 100 Ω, 200 Ω and 300 Ω, connected in series?
- AAbout 55 Ω
- B600 Ω
- C200 Ω
Show answer and explanation
Answer: B. 600 Ω
The combined resistance of resistors in series is their sum: 100 + 200 + 300 = 600 Ω. The same current flows through all three, and the voltage divides in proportion to resistance. Applying 12 V, for example, gives a current of 12 V/600 Ω = 20 mA and voltages of 2 V, 4 V and 6 V across the resistors. With the same three in parallel, the combined resistance is about 55 Ω, smaller than the smallest resistor (100 Ω).
- A. About 55 Ω is the combined resistance of the three in parallel.
- B. Correct. Series resistances add, giving 600 Ω.
- C. 200 Ω is the average of the three, not the combined resistance.
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