A source uniformly radiates 31.4 W of radiant flux in all directions. If the luminous efficiency is 60 lumen watt^ -1 , determine the luminous intensity of the source.

Correct answer: D. 150 cd Total luminous flux = Radiant flux × Luminous efficiency = 31.4 × 60 = 1884 lm For a source radiating uniformly in all directions, the total solid angle is 4π sr . Luminous intensity I = ( )/(4π) I = (1884)/(4 × 3.14) = (1884)/(12.56) = 150 cd

Concepts Of Physics MCQ Edition [Volume 1]

Exam: Concepts Of Physics MCQ Edition [Volume 1]
Subject: Physics
Chapter: Photometry

Concepts Of Physics MCQ Edition [Volume 1] · Physics · Photometry

A source uniformly radiates 31.4 W of radiant flux in all...

A source uniformly radiates

31.4 \text{ W}

of radiant flux in all directions. If the luminous efficiency is

60 \text{ lumen watt}^{-1}

, determine the luminous intensity of the source.

Options

A $600 \text{ cd}$
B $300 \text{ cd}$
C $1884 \text{ cd}$
D $150 \text{ cd}$

Correct answer

D. $150 \text{ cd}$

Step-by-step solution

Total luminous flux

\Phi = \text{Radiant flux} \times \text{Luminous efficiency}

\Phi = 31.4 \times 60 = 1884 \text{ lm}

For a source radiating uniformly in all directions, the total solid angle is

4\pi \text{ sr}

.

Luminous intensity

I = \dfrac{\Phi}{4\pi}

I = \dfrac{1884}{4 \times 3.14} = \dfrac{1884}{12.56} = 150 \text{ cd}

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