A lamp having mean spherical candle power of 800 is suspended at the height of 10 m. Calculate the illumination just before the lamp-a)8000 luxb)81 luxc)80 luxd)800 luxCorrect answer is option 'B'. Can you explain this answer?

Question

Answer

To calculate the illumination just before the lamp, we need to use the formula:

Illumination = Luminous Intensity / (Distance^2)

Given:
Mean Spherical Candle Power (Luminous Intensity) = 800
Height of the lamp = 10 m

Calculations:
1. Convert Mean Spherical Candle Power to Luminous Intensity:
Luminous Intensity (in candelas) = Mean Spherical Candle Power (in lumens) / 4π
Luminous Intensity = 800 / (4 * 3.14) ≈ 63.96 cd

2. Calculate the distance from the lamp to the point where illumination is to be measured:
The distance from the lamp to the point where illumination is to be measured is the height of the lamp, which is 10 m.

3. Plug the values into the formula:
Illumination = 63.96 cd / (10^2)
Illumination = 63.96 / 100
Illumination ≈ 0.64 lux

Therefore, the correct answer is option 'B' which states that the illumination just before the lamp is approximately 0.64 lux.

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