Two plastic spheres The figure shows two thin plastic spherical shells (shown in

Question

Two plastic spheres The figure shows two thin plastic spherical shells (shown in cross section ) that are uniformly charged. The center of the larger sphere is a t ; it has a radius o f 12 cm and a uniform positive charge o f 5 x 10 -9 C . The center of the smaller sphere is a t cm ; it has a radius o f 3 cm and a uniform negative charge of -3 x 10'9 C. W h a t is the electric field a t location A (6 cm to the right o f the center o f the large sphere)? Neglect the small contribution o f the polarized molecules in the plastic, because the shells are very thin and don't contain much matter. N/C W h a t is the electric field a t location B (1 5 cm above the center o f the small sphere)? Again, neglect the small contribution o f the polarized molecules in the plastic, because the shells are very thin and don't contain much matter N/C What is the force on an electron placed at location B? N

Explanation / Answer

let

charge on small sphere is q1=3*10^-9 C

charge on big sphere is q2=5*10^-9 C

a)

at point A, electric field due to spherical sphere is zero

E=0

b)

electric field due to small sphere is, E1=k*q1/r^2

E1=9*10^9*3*10^-9/(0.15)^2

E1=1200 N/C

and

electric field due to large sphere is, E2=k*q2/r^2

E2=9*10^9*5*10^-9/(0.25^2+0.15^2)

E2=529.412 N/C

Enet=E1+E2

=-1200+529.412

=670.59 N/C

c)

force on electron is,

F=q*E

=1.6*10^-19*670.59

=1.073*10^-16 N

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