Question

If 5% of the energy supplied to a bulb is irradiated as visible light, how many quanta are emitted per second by a 100 W lamp? Assume wavelength of visible light of $5.6\times {10}^{-5}cm$.

• A. $1.4\times {10}^{19}$
• B. $3\times {10}^3$
• C. $1.4\times {10}^{-19}$
• D. $3\times {10}^4$

Answer 1

The correct option is A $1.4\times {10}^{19}$

Let n be the emitted photons per sec.

We know that photon energy , $E=h\nu =\frac{hc}{\lambda }$

here, $nE=5$

So, $n=\frac{5\lambda }{hc}=\frac{5\times 5.6\times {10}^{-7}}{(6.62\times {10}^{-34})\times (3\times {10}^8)}=1.4\times {10}^{19}$