Class-12th Physics,
Electric Charges and Fields,
Chapter-1, Exercise -1, Q-1.21
NCERT Solutions for Class 12th Physics
A conducting sphere of radius 10 cm has an unknown charge. If the electric field 20 cm from the centre of the sphere is 1.5 × 10³N/C and points radially inward, what is the net charge on the sphere?
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Electric field intensity (E) at a distance (d) from the centre of a sphere containing net charge q is given by the relation,
E= 1 /4πε0 x q/d²
Where, q = Net charge = 1.5 x 103 N/C
d = Distance from the centre of sphere = 20 cm = 0.2 m
ε0 = Permittivity of free space and
1 /4πε0 = 9 x109Nm2C⁻2
Therefore,
q = E(4πε0)d2 =
=(1.5 x 10³) (0.2)2 / (9 x 109)
6.67 x 10⁻9C =6.67 nC
Therefore, the net charge on the sphere is 6.67 nC.