Resistors of 10 Ω, 20 Ω and 30 Ω are connected in series. What is the total resistance?
Answer in Ω.
Show the answer
60 Ω
RT = R1 + R2 + R3 = 10 + 20 + 30 = 60 Ω.
Reference: Series circuit rule: RT = R1 + R2 + R3
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Series parallel practice questions
30 questions from the electrical theory and calculations practice test.
Series parallel practice test
10 questions, graded as you go, with the reason for every answer. No sign-up.
What this covers
- Series circuits
- Parallel circuits
- Voltage dividers
- Kirchhoff's laws
- Combination circuits
Sample questions
A 20 Ω resistor and a 30 Ω resistor are connected in parallel. What is the total resistance?
Answer in Ω.
Show the answer
12 Ω
RT = (R1 × R2) ÷ (R1 + R2) = (20 × 30) ÷ (20 + 30) = 600 ÷ 50 = 12 Ω.
Reference: Parallel circuit rule: RT = (R1 × R2) ÷ (R1 + R2)
Three 30 Ω resistors are connected in parallel. What is the total resistance?
- 90 Ω
- 10 Ω
- 30 Ω
- 15 Ω
Show the answer
B. 10 Ω
For equal resistors in parallel, RT = R ÷ N = 30 ÷ 3 = 10 Ω. 90 Ω is the series total, which is the usual mix-up.
Reference: Parallel circuit rule: equal resistors, RT = R ÷ N