- #1
bcjochim07
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Homework Statement
#1
A -10 nC charge and a +20 nC charge are 15cm apart on the x-axis. What is the electric potential at the spot where electric field = 0?
So called the 20nC charge q1 & the -10 nC charge q2.
I also defined r1 as distance from the 20nC charge, so r2 must then = .15 + q1
so Kq1/(r1)^2 = Kq2/(r1 +.15)^2 but when I put in the values and solve the resulting quadratic, I get a negative radius. If I switch how I assigned the charges, however, I get the correct answer. Why must my r1 be the distance from the -10 nC charge?
#2
Two 10 cm diameter electrodes are .50cm apart to form a parallel plate capacitor. The electrodes are attached to a 15V battery. Insulating handles are used to pull the electrodes away from each other until they are 1 cm apart. The electrodes remain connected to the battery during this process. What is the electric field after this process?
When they aren't pulled away deltaV = (.005m)E E= 3000V/m
I'm thinking that E should be constant because E = surface charge density / permittivity constant, but when they are pulled apart I find that:
V=Ed (15 V ) = E (.01) E = 1500 V/m. How can this change?