A charged paint is spread in a very thin uniform layer over the surface of a plastic sphere of diameter 15.0 cm , giving it a charge of -20.0 μC .
Part A
Find the electric field just inside the paint layer.
Part B
Find the electric field just outside the paint layer.
Part C
Find the electric field 6.50 cm outside the surface of the paint layer.
A)
EA=Q/Eo= 0 <<<<<<<<
———————————————————————
B)
Q= -20.0 μC
EA=Q/Eo
E x 4pi(0.075^2)=(20.0×10^-6)/(8.854×10^-12)
E=3.196×10^7 <<<<<<<<<<
————————————————-
C)
4pi(0.075+0.065)^2
4pi(0.15)^2
E x 4pi(0.14^2)=(20.0×10^-6) / (8.854×10^-12)
E=5.56×10^5 <<<<<<<<<
1 Answer
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A) Exactly — flux = E*A = Q / εo
But the “enclosed charge” Q “just under the paint layer” is 0, so
the field E = 0 N/C (everywhere inside the paint layer).
B) This one looks set up fine. I’d round the result to 3.20e7 N/C.
C) Set up OK, but you erred in the first step — you should have
4pi(0.15)^2
Oh, wait; I see you’ve corrected that in the actual calculation.
But I still think you’ve made a calculator error somewhere.
I get 9.17e6 N/C.
Hope this helps!
