Electrostatics Question 510
Question: At a point 20 cm from the centre of a uniformly charged dielectric sphere of radius 10 cm, the electric field is 100 V/m. The electric field at 3 cm from the centre of the sphere will be [BCECE 2005]
Options:
A) 150 V/m
B) 125 V/m
C) 120 V/m
D) Zero
Show Answer
Answer:
Correct Answer: C
Solution:
Electric field outside of the sphere $ E _{out}=\frac{kQ}{r^{2}} $ …(i)
Electric field inside the dielectric sphere $ E _{in}=\frac{kQx}{R^{3}} $ …(ii)
From (i) and (ii), $ E _{in}=E _{out}\times \frac{r^{2}x}{R} $
therefore At 3 cm, $ E=100\times \frac{3{{(20)}^{2}}}{10^{3}}=120V/m $
