Question

Two sources A and B have same power. The wavelength of radiation of A is ${\lambda }_a$ and that of B is ${\lambda }_b$. The number of photons emitted per second by A and B are $n_a$ & $n_b$ respectively, then,

• A. ${\lambda }_a>{\lambda }_b$
• B. if ${\lambda }_a>{\lambda }_b$, $n_a<n_b$
• C. if ${\lambda }_a<{\lambda }_b$, $n_a<n_b$
• D. if ${\lambda }_a>{\lambda }_b$, $n_a=n_b$

Answer 1

Answer: (C)

if ${\lambda }_a<{\lambda }_b$, $n_a<n_b$

$n=\frac{P\lambda }{hc}$

$\therefore n\propto \lambda$

So, the answer is option (C).