A 60W electric bulb is kept switched on continuously for 10h. Assuming all the electrical energy ultimately leaves the circuit as light and heat, what is the decrease in the rest mass of the energy source that powered the bulb?
(a) 2.4×10−10kg
(b) 2.4×10−11kg
(c) 7.2×10−11kg
(d) 2.4×10−12kg