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Question
Let nr and nb be the number of photons emitted by a red bulb and a blue bulb, respectively, of equal power in a given time.
Options
nr = nb
nr < nb
nr > nb
The information is insufficient to derive a relation between nr and nb.
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Solution
nr > nb
The two bulbs are of equal power. It means that they consume equal amount of energy per unit time.
Now, as the frequency of blue light `(f_b)` is higher than the frequency of red light `(f_r)` , `hf_b > hf_r`
Hence, the energy of a photon of blue light is more than the energy of a photon of red light.
Thus, a photon of blue light requires more energy than a photon of red light to be emitted.
For the same energy given to the bulbs in a certain time, the number of photons of blue light will be less than that of red light.
∴ `n_r > n_b` (As the amount of energy emitted from the two bulb is same)
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