Q.


SI unit of intensity of light is:


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a

Newton

b

Kelvin

c

Kilogram

d

Candela 

answer is D.

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Detailed Solution

Concept- We will first examine the definition of light intensity in this query. Both electric and magnetic fields are present in light. These amounts all have energy. As a result, we will calculate the light's intensity using the wave's energy idea and then obtain the SI unit for light intensity.
Let Question Image be the pointing vector then the magnitude of the pointing vector gives the power per unit area of the wave.
Question ImageWhere are the current values at the observation point, and?
The fact that
Question ImageWhere, Question Image is speed of light
We can also write:
Question ImageThe Pointing vector Question Image fluctuates very rapidly with time. The frequency is about Question Image.
Intensity of light:-
It is defined as the time average of magnitude of pointing vector ' Question Image '.
Question ImageThe average value of Question Image function is Question Image. We thus obtain:
Question ImageThe intensity of light may also be expressed in terms of rms magnitude of the fields. With Question Image, we obtain
Question ImageThe unit of intensity of light is Candela.
Hence, option 4 is correct.
 
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