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gupt · Mar 9, 2012, 04:24 AM

Two capacitors a and b are connected in series across a 10v battery. The voltages across a and b are found to be 6V and 4V respectively. If another 2microfarad capacitor is connected across a the voltage across b increases to 9V. Calculate the capacitances of a and b.

gupt · Mar 9, 2012, 04:25 AM

Hw to do that sum?

ebaines · Mar 9, 2012, 06:54 AM

You can use the relatonship $Q=CV$ , and since the charge on both capacitors is equal you get

$<br /> 6C_a = 4 C_b<br />$

Then when you add the 2 $\mu$ F capacitor to a it's capacitance becomes $C_a + \mu$ F, and since the votage across b is now 9 that means the voltage across a is 1. So your second equation is

$<br /> 1(C_a+2 \mu F) = 9 C_b<br />$

Now you have two equations is two unknowns, and you can solve for the capacitances of a and b.