Question

The number of photons emitted in 10 hours by a 60 W sodium lamp are:

(take $\lambda$ of photon $=$ 6000 A, $hc$ $=$ 12400 eVA, h $=$ Planck's constant, $c$ $=$ speed of light)

• A. $6.50\times {10}^{24}$
• B. $6.40\times {10}^{23}$
• C. $8.40\times {10}^{23}$
• D. $3.40\times {10}^{23}$

Answer 1

The correct option is A $6.50\times {10}^{24}$

Let $n$ be the number of photons emitted.
An energy of $n$ photons = Energy dissipated in 10 hours.

$\frac{h\times c\times n}{\lambda }=60\times 10\times 60\times 60$
$\frac{12400}{6000}\times 1.6\times {10}^{(-19)}\times n=60\times 10\times 60\times 60$
$n=6.5\times {10}^{24}$