A battery of emf and internal resistance is connected to a fixed resistor in parallel with a variable resistor . The maximum power that can be delivered to as is varied is

Answer and explanation

Correct answer: D.

  1. Step 1: Find the Thévenin equivalent of the circuit connected across the variable resistor . Open-circuit voltage across is .
  2. Step 2: Determine the Thévenin resistance by deactivating the independent source: .
  3. Step 3: By the maximum power transfer theorem, maximum power delivery occurs when the load equals the source resistance (), yielding .
Answer
.
Why not the others: ignores the fixed parallel resistor entirely.

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