Question
Question: Two opposite and equal charges 4 × 10<sup>–8</sup>*coulomb* when placed 2 × 10<sup>–2</sup>*cm* away...
Two opposite and equal charges 4 × 10–8coulomb when placed 2 × 10–2cm away, form a dipole. If this dipole is placed in an external electric field 4 × 108newton/coulomb, the value of maximum torque and the work done in rotating it through 1800 will be
A
64 × 10–4Nm and 64 × 10–4J
B
32 × 10–4Nm and 32 × 10–4J
C
64 × 10–4Nm and 32 × 10–4J
D
32 × 10–4Nm and 64 × 10–4J
Answer
32 × 10–4Nm and 64 × 10–4J
Explanation
Solution
τmax = pE and Wmax = 2pE p = Q × 2l = 4 × 10–8 × 2 × 10–2 × 10–2 = 8 × 10–12 C-m
So, τmax = 8 × 10–12 × 4 × 108 = 32 × 10–4 N-m and Wmax = 2 × 32 × 10–4 = 64 × 10–4 J