15. The emf of a battery is 12 volts. When the battery delivers a current of 0.5 ampere to a load, the potential difference between the terminals of the battery is 10 volts. The internal resistance of the battery is
(A) 1Ω
(B) 2Ω
(C) 4Ω
(D) 20Ω
(E) 24Ω
(A) 1Ω
(B) 2Ω
(C) 4Ω
(D) 20Ω
(E) 24Ω