Suspended from a sensitive balance is a 100 W bulb along with its power supply. Determine the change in the recorded mass after the bulb is kept on for 1 year .

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Correct answer: C. 3.5 × 10^ -8 kg

The energy radiated by the bulb in one year is given by

E = P \times t

.

Substituting the given values:

P = 100 \text{ W}

t = 1 \text{ year} = 365 \times 24 \times 60 \times 60 \text{ s} = 3.1536 \times 10^7 \text{ s}

E = 100 \times 3.1536 \times 10^7 = 3.1536 \times 10^9 \text{ J}

According to the mass-energy equivalence principle, the energy leaving the system as light and heat results in a decrease in the mass of the system.

\Delta m = \dfrac{E}{c^2}

\Delta m = \dfrac{3.1536 \times 10^9}{(3 \times 10^8)^2}

\Delta m = \dfrac{3.1536 \times 10^9}{9 \times 10^{16}}

\Delta m = 0.3504 \times 10^{-7} \text{ kg} \approx 3.5 \times 10^{-8} \text{ kg}

Suspended from a sensitive balance is a 100 W bulb along with its...

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