A fluorescent tube which is equivalent to a line source of $100$ candela per meter is hung horizontally $5$ meters above the table. The illuminance at a point vertically below the tube will be

8

lux

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8

phot

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40

lux

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40

phot

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Solution

The correct option is A $40$ lux

$\frac{F}{4 π} = 100$
$F = 400 π$

therefore illuminance at a point vertically below
$\frac{F}{2 π 40 l u x d} = \frac{400 π}{2 π \times 5} = 40 l u x$

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A fluorescent tube which is equivalent to a line source of 100 candela per meter is hung horizontally 5 meters above the table. The illuminance at a point vertically below the tube will be

The correct option is A 40 luxF4π=100F=400πtherefore illuminance at a point vertically belowF2π 40 luxd=400π2π×5=40lux

A fluorescent tube which is equivalent to a line source of $100$ candela per meter is hung horizontally $5$ meters above the table. The illuminance at a point vertically below the tube will be

The correct option is A $40$ lux

$\frac{F}{4 π} = 100$
$F = 400 π$

therefore illuminance at a point vertically below
$\frac{F}{2 π 40 l u x d} = \frac{400 π}{2 π \times 5} = 40 l u x$