Current Electricity and Electrical InstrumentHard

Question

Choose the correct alternatives

Options

A.It is easier to start a car engine on a warm day than on a chilly cold day because the internal resistance of battery decreases with rise in temperature
B.It is more economical to transmit electric power at high voltage and low current rather than at low voltage and high current because heat loss is proportional to square of current.
C.The heating coil of an electric iron is enclosed in mica sheets because mica is a bad conductor of heat and good conductor of electricity
D.The heating coil of an electric iron is enclosed in mica sheets because mica is a good conductor of heat and bad conductor of electricity.

Solution

It is easier to start a car engine on a warm day than on a chilly cold day because the internal resistance of battery decreases with rise in temperature and so current increases.
Power Loss = I2R,      ⇒      Power loss ∝ I2
also P = V.I         ⇒         I = P/V
since for given power & line P & R are constant
Power loss  = I2R =        ∴   Power loss ∝ 1/V2
mica is good conductor of heat but bad conductor of electricity

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