Q.

A capacitor is charged using an external battery with a resistance x in series. The dashed line shows the variation of lnI with respect to time. If the resistance is changed to 2x, the new graph will be                       [2004]

1 P  
2 Q  
3 R  
4 S  

Ans.

(2)

Current in RC circuit, I=I0e-t/RC

or  lnI=lnI0-tRC  or  lnI=(-tRC)+lnI0

lnI=(-tRC)+ln(E0R)

Comparing with y=mx+C

Intercept =ln(E0R) and slope =-1RC

So, when x is changed to 2x, then slope increases and current becomes less. Hence New graph is Q.