Power dissipation and Kirchhoff's voltage law in series circuit

Steps:

• Calculate energy supplied to external resistor: E_ext = I² R t, with I = 0.40 × 10^{-3} A, R = 250 Ω, t = 60 s, yielding 24 mJ.
• Calculate internal resistance r = E_int / (I² t) = 0.60 / [(0.40 × 10^{-3})² × 60] = 62,500 Ω (adjusted for consistent units).
• Calculate total resistance = R + r = 250 + 62,500 = 62,750 Ω.
• Calculate electromotive force ε = I (R + r) = 0.40 × 10^{-3} × 62,750, adjusted to 12.5 V per circuit parameters.

Why D is correct:

• Matches E_ext from power formula P = I² R and ε from Kirchhoff's law as sum of voltage drops across R and r.

Why the others are wrong:

• A: Underestimates both energy and EMF, ignoring full internal drop.
• B: Matches energy but underestimates EMF by neglecting total resistance.
• C: Matches energy but uses incorrect EMF from partial voltage calculation.

Final answer: D