Question

A bulb emits light of $\lambda =4500\stackrel{o}{\text{A}}$. The bulb is rated as 150 watt and 8% of the energy is emitted as light. How many photons are emitted by the bulb per second?

• A. $27.2\times {10}^{18}$
• B. $2.72\times {10}^{16}$
• C. $2.72\times {10}^{18}$
• D. $0.272\times {10}^{18}$

Answer 1

The correct option is A $27.2\times {10}^{18}$

Energy of one photon
$=E=hv=\frac{hc}{v}$
$=\frac{6.626\times {10}^{-34}\times 3\times {10}^8}{4500\times {10}^{-10}}=4.42\times {10}^{-19}\text{J}$
Energy emitted by bulb $=\frac{150\times 8}{100}\text{J}$
$\therefore n\times 4.42\times {10}^{-19}=\frac{150\times 8}{100}$

$\therefore n=27.2\times {10}^{18}$ photons