Q1:A spherical uniform charge distribution of total charge +0.02 C and radius 3cm is placed at the origin?

Q1:A spherical uniform charge distribution of total charge +0.02 C and radius 3cm is placed at the origin of the x, y, z co-ordinate system, and an electron is located at position (-2, 0, 0) cm . The electron is moved to a new position, (5, 4, 5) cm. Assume that the zero position for the electric potential is at infinity.








(a) Find the potential at the two positions of the electron, and the potential difference between them.


(b)Does the electron gain or lose potential energy in moving to the new position?


(c)How much potential energy is gained or lost? Express the answer both in electron Volts and Joules.

Q1:A spherical uniform charge distribution of total charge +0.02 C and radius 3cm is placed at the origin?
position 1 the electron is inside the sphere of charge


Use Gauss law to get the E-field (you need to work out the fraction of charge Q enclosed by your spherical gauss surface -its radius =2cm)


4*pi*r^2*E=Q*r^3/(eo*R^3)..Q=0.02C r=2cm R=3cm etc


%26gt;E=Q*r/(4*pi*eo*R^3)


%26gt;V1=-Q*r^2/(8*pi*eo*R^3)+ const integrating (E=-dV/dr)


Const=V at r=0=3*Q/(8*pi*eo*R) (this requires proof btw!)


%26gt;V1=3*Q/(8*pi*eo*R)- Q*r^2/(8*pi*eo*R^3)


Next bit looks simple


V2=-Q/(4*pi*eo*r) r=sqrt(5^2+4^2+5^2) since your charge distrib is spherically symnetrical (remember to convert cm to metres)


a) Now just subtract after inserting values (1/(4*pi*eo)=10^9)


b) loses? ..work it out!


c) change in Ep= (V2-V1)*electron charge for joules


and just equal to V2-V1 for electron volts