Question -A solid metallic sphere has a charge + 3Q. concentric with this sphere is a conducting spherical shell havingcharge –Q. The radius of the sphere is a and that of the spherical shell is b. (b > a). What is the electric field at a distance R (a < R < b) from the centre.
Options:
A .  Q2πϵ0R
B .  3Q2πϵ0R
C .  3Q4πϵ0R2
D .  4Q2πϵ0R2
E .  If assertion is false but reason is true.
Answer: Option C : C We only need to consider the E contribution due to sphere. Shell gives zero contribution to E at any point inside it. Use direct formula. E=14πϵ03QR2 E=3Q4πϵ0R2
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