Calculate capacitance of conductors

[s-f]

Problem: (a) What is the capacitance of the 2 conductors +20nC and -20nC? (b) If the voltage difference between the 2 conductors increase to 250 V, then what else changes?

a). I calculated that ΔV = 100 V. So then I plugged into the formula C = Q/ΔV. I thought 20 nC = 2 x 10^-8 C, which divided by 100 V = 2 x 10^-9C but the answer is 2 x 10^-10 C. What am I doing wrong? I know this is very simple but I have never studied physics before and am terrible at math.

b). charge of the conductors increases to keep capacitance constant, since capacitance is a property of area and distance between plates (I think this is right but please tell me if it's wrong!)

Thanks in advance!

 

[berkeman]

Problem: (a) What is the capacitance of the 2 conductors +20nC and -20nC? (b) If the voltage difference between the 2 conductors increase to 250 V, then what else changes?

a). I calculated that ΔV = 100 V. So then I plugged into the formula C = Q/ΔV. I thought 20 nC = 2 x 10^-8 C, which divided by 100 V = 2 x 10^-9C but the answer is 2 x 10^-10 C. What am I doing wrong? I know this is very simple but I have never studied physics before and am terrible at math.

b). charge of the conductors increases to keep capacitance constant, since capacitance is a property of area and distance between plates (I think this is right but please tell me if it's wrong!)

Thanks in advance!

Welcome to the PF.

Where did the 100V come from? Is it given for part a)?

 

[s-f]

Thanks. Actually the problem had more steps before this and Ohm's Law was used to calculate Voltage = 100 V (I have the answers so I know it's correct). The part I'm unsure of is how C = 2 x 10^-10 Farads (not Coulombs - I accidentally wrote C instead of F earlier!).

 

[s-f]

Anyone? I would really appreciate it : )