Question

A green bulb and a red bulb are emitting the radiations with equal power. The correct relation between numbers of photons emitted by the bulbs per second is:
number of photons of green bulb = $n_g$ and $\lambda =570nm$
number of photons of red bulb = $n_r$ and $\lambda =700nm$

• A. $n_g=n_r$
• B. $n_g<n_r$
• C. $n_g>n_r$
• D. Unpredictable

Answer 1

The correct option is B $n_g<n_r$

Power of both the bulbs are equal i.e. $E_g=E_r$
We know, E = $nhv$ = $\frac{hc}{\lambda }$
So, $n_g\times \frac{hc}{{\lambda }_g}=n_r\times \frac{hc}{{\lambda }_r}$
Since, $\lambda$ of red bulb = 700 nm, $\lambda$ of green bulb = 570 nm
$\Rightarrow \frac{n_g}{n_r}=\frac{{\lambda }_g}{{\lambda }_r}=\frac{570}{700}<1$
So, $n_g<n_r$