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The coil of an electric bulb takes 40 wa...

The coil of an electric bulb takes 40 watts to start glowing. If more than 40 W is supplied, 60% of the extra power is converted into light and the remaining into heat. The bulb consumes 100 W at 220 V. Find the percentage drop in the light intensity at a point if the supply voltage changes from `220 V to 200 V`.

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The correct Answer is:
B
`P = 100W, V = 220V Case- I : Excess power = 100 -40 = 60W` Power converted to light =` 36 W` Case -II: Power = `82.64 - 40 = 42.64xx60 = 25.584 W p= 36-25.584 = (10,416)/(36) xx100 = 28.93 = 29%`
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HC VERMA-THERMAL AND CHEMICAL EFFECT OF ELECTRIC CURRENT-Exercise
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  2. An electric bulb, when connected across a power supply of 220V, consum...

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  3. A servo voltage stabiliser restricts the voltage output to 220 V +- 1%...

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  4. An electric bulb marked 220 V, 100 W will get fused if it is made to c...

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  5. An immersion heater rated 1000 W, 220 V is used to heat 0.01 m^3 of wa...

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  6. An electric kettle used to prepare tea, takes 2 minutes to boil 4 cups...

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  7. The coil of an electric bulb takes 40 watts to start glowing. If more ...

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  8. The 2.0 Omega resistor show in figure is dipped into a calorimeter con...

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  13. Find the amount of silver liberated at cathode if 0.500 A of current i...

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  15. Find the time requried to liberate 1.0 litre of hydrogen at STP in an...

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  16. Two voltameters, one having a solution of silver salt and the other of...

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  17. A brass plate having surface area 200 cm^2 on one side is electroplate...

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  18. Figure, shows an electrolyte of AgCI through which a current is passed...

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  19. The potential difference across the terminals of a battery of emf 12 V...

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  20. A plate of area 10 cm^2 is to be electroplated with copper (density 90...

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