A lamp hangs at a height of 4.0 m above a table. The lamp is lowered by 100 cm. The illuminance on the table increases by __%.
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The only change when lamp moves from 4 m to 3 m is its d
Illuminance at 4 m = Power / 16
Illuminance at 3 m = Power / 9
Increase in Illuminance =
power / 9 - power/16 = 7power/144
so% increase = 7 power / 144 × 16×100/power
= 77.77%
= 78%
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