Physics

Problem

A coil of inductance

L=0.15\,\text{H}

in series with a resistor

R=40\,\Omega

is connected to a

200\,\text{V}

(rms),

60\,\text{Hz}

ac mains. A capacitor of capacitance

C

is also connected in series. (i) If

C=80\,\mu\text{F}

, calculate the rms current drawn from the supply. (ii) The capacitance is now adjusted so that the current becomes maximum at

60\,\text{Hz}

. Find the new value of

C

required. (iii) Keeping the value of

C

found in part (ii), the supply frequency is suddenly doubled to

120\,\text{Hz}

while the supply voltage remains the same. Calculate the new rms current and explain qualitatively why it differs from the value obtained in part (ii).

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