Resistors in parallel combination

Steps:

• Identify the circuit configuration: one R1 and two R2 resistors connected in parallel across the cell.
• For resistors in parallel, the reciprocal of total resistance equals the sum of reciprocals of individual resistances.
• Write the equation: 1/R = 1/R1 + 1/R2 + 1/R2.
• Simplify if needed, but the given form matches option D.

Why D is correct:

• Parallel resistors follow the law 1/R_total = Σ (1/R_i), so for R1 and two R2's, it is exactly 1/R = 1/R1 + 1/R2 + 1/R2.

Why the others are wrong:

• A assumes all three in series, adding resistances directly, which ignores parallel setup.
• B omits the second R2, treating only one R1 and one R2 in parallel.
• C incorrectly uses two R1's in parallel, ignoring the R2 values.

Final answer: D