Question

Let $n_r$ and $n_b$ be respectively the number of photons emitted by a red bulb and a blue bulb of equal power in one second.

• A. n_r = n_b
• B. n_r<n_b
• C. n_r>n_b
• D. The information is insufficient to get a relation between n_r and n_b.

Answer 1

The correct option is C

n_r>n_b

Let ν_r and $v_b$ be the freqencies of red and blue light respectively. We know that $v_b>v_r$. Also, $n_r$ red photons and $n_b$ blue photons are emitted each second.

Now, since the two sources emit with equal power, the energy emitted per second will be -

$n_r\left(h{v}_r\right)=n_b\left(h{v}_b\right),$

which would imply,

$n_r{v}_r=n_b{v}_b.$

Since $v_b>v_r$, we can directly conclude: $n_r>n_b$! Option (c) is correct.