A bulb is rated at 150 watt, converting 8% energy into light. If energy of one photon is 4.42×10−19J, how many photons are emitted by the bulb per second?

First, determine how much of the bulb’s electrical power is turned into light. The bulb consumes $150 W$ and only $8\%$ of that power is emitted as light.

$P=150 W\backslash times0.08$

This gives a luminous power of

$12 J/s$

Each photon carries an energy of $4.42\times {10}^{-19} J$. To find the number of photons emitted each second, divide the total light energy per second by the energy of one photon:

$N=\frac{12}{4.42\times {10}^{-19} J}$

Carrying out the division:

$12\backslash div4.42\backslash approx2.715$

and combining the powers of ten:

$2.715\backslash times10{19}^{}$

Rounding to three significant figures, the bulb emits approximately

$2.71\backslash times10{19}^{} \mathrm{photons}/s$

This matches the given correct option.