Question

Two bulbs $A$ and $B$ emit red light and yellow light at $8000A^{\circ }$ and $4000A^{\circ }$ respectively. The number of photons emitted by both the bulbs per second is the same. If the red bulb is labelled as $100$ watts, find the wattage of the yellow bulb.

• A. 200.00
• B. 200
• C. 200.0

Answer 1

Answer: (A), (B), (C)

Let, $n$ be the no. of photons emitted by bulbs per second & $W$ be the wattage of yellow bulb.
Since, Power (Wattage) $=n\times$ Energy of one photon
For red bulb, $100=n\times \frac{12400}{8000}\times 1.6\times {10}^{-19}$ ...(i)
For yellow bulb, $W=n\times \frac{12400}{4000}\times 1.6\times {10}^{-19}$ ...(ii)
Since, value of $n$ i.e. number of electrons emitted per second, is same for both bulb, we can solve (i) and (ii), we get:
$W=200$ watts