Question
Negative charge -1nC is distributed uniformly throughout an insulating sphere of radius 8cm, centered at the origin. A particle with negative charge -1nC is placed at x = 16cm on the x- axis. They may of the electric field in N/C at x = 4cm on the x-axis is A. 900, directed to -ve x-axis B. 78, directed to +ve x-axis C. 450 directed +ve x-axis D. 849. directed to -ve x-axis E. none of these Positive charge Q is placed on a conducting spherical shell with inner radius R_1 and outer Radius, R_2. A point charge q is placed at the center of the cavity. The magnitude of the electric field at a point outside the shell, a distance r from the center, is: A. zero B. Q/4 pi epsilon_0 r^2 C. q/4 pi epsilon_0 r^2 D. (q + Q)/4 pi epsilon_0 r^2 E. (q + Q)/4 pi epsilon_0 R_1^2 - r^2)
Explanation / Answer
Inside the sphere, spherical charge is distributed
Charge inside a 4cm sphere Q =Qo*r^3/(R^3)
(Q= Volume of sphere of radius r /Volume of sphere of radius R *charge )
=>Q =1nC*4^3/8^3 =1/8nC
=>E =k*q/r^2 =8.99*10^9*(1/8*10^-9)/0.04^2 =702.34 N/C
Direction of a field produced by negative charge is pointed towards it i.e field towards the sphere.
B) E =k*(Q+q)/r^2
(Charge placed at centre of cavity and charge on sphere both acts as they are at centre when field is outside R2)