A 200 W sodium street lamp emits yellow light of wavelength 0.6 μm. Assuming it to be 25% efficient in converting electrical energy to light, the number of photons of yellow light it emits per second is

Explanation

To solve the problem of finding the number of photons emitted per second by a sodium street lamp, we can follow these steps:

### Step 1: Calculate the total power converted to light
The lamp has a power of 200 W and is 25% efficient in converting electrical energy to light. Therefore, the power converted to light (P_light) can be calculated as:

\[ P_{\text{light}} = \text{Efficiency} \times P_{\text{total}} = 0.25 \times 200 \, \text{W} = 50 \, \text{W} \]
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