1.

A parallel plate capacitor in series with a resistance of 100 Omega, an inductor of 20 mH and and AC voltage source of variable frequency shows resonance at a frequency of (1250)/(pi)Hz. If this capacitor is charged by a DC voltage source to a voltage 25 V, what amount of charge will be stored in each plate of the capacitor ?

Answer»

`0.2 mu C`
`2 MC
0.2 mC
0.2 C

SOLUTION :Reasonant frequency, `omega_(r )=2pi upsilon_(r )=(1)/(sqrt(LC))`
`rArr 4PI^(2)upsilon_(r )^(2)=(1)/(LC)rArr C=(1)/(4pi^(2)upsilon_(r )^(2)L)`
`rArr C=(pi^(2))/(4pi^(2)xx(1250)^(2)xx20xx10^(-3))=8XX10^(-6)F`
Now, the capacitor is charged by a voltage source of 25 V, charge stored = Q = CV
`=8xx10^(-6)xx25=200xx10^(-6)=0.2xx10^(-3)C`
`therefore Q=0.2 mC`


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