(MCQ) "Invertion of Electric Bulb" CBSE/NCERT Science Class 7|#BrightIQ | #Shorts

A box contains 20 electric bulbs,out of which 4 are defective.Two balls are chosen at random from this box.The probability that at least one of them is defective,is (4)/(19) (b) (7)/(19) (c) (12)/(19) (d) (21)/(95) (e) None of these

The temperature of the tungsten filament of a 60 W electric bulb is T= 2000 K. Find the surface area ofthe filament. The emmissivity of the surface is e= 0.30. Neglect radiation received from surrounding. Take sigma=5.7xx10^(-8)w//M^(2)k.

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