Answer: 20 ohm.
- A 20 ohm
- B 30 ohm
- C 45 ohm
- D 60 ohm
Correct answer: A. 20 ohm
Explanation: X/Y = l1/(100-l1) = 40/60 = 2/3. X = Y x 2/3 = 30 x 2/3 = 20 ohm.
In series, the same current flows through both resistors; in parallel, the current splits between branches and the voltage across each resistor is the same.
Concept context
Ohm's law, resistors, Kirchhoff's laws, Wheatstone bridge, and cells.