N identical capacitors each " of capacitances "C" when connected in parallel gives effective capacitance `90 mu F` and when connected in series gives `5mu F`.The value of "N" and "C" approximately are

Options

A. `6 and 15 muF`
B. `6 and 18 muF`
C. `15 and 6 muF`
D. `18 and 5 muF`

Answer

A

Explanation

`C_S=C/n =2.5 implies C=2.5 n`
`C_p = nC = 90 implies C = 90/n`
`90/n = 2.5n, n^2 = (900)/25 =36`
`implies n = 6 and C = 15 muF`