Field of a charged sphere and potential
Answers are for parents and teachers.
1
In air, what is E on the surface of a sphere with R = 0.2 m, q = 20 nC (N/C)? (k = 9·10⁹)
4500
2
Two charges in air exert 0.6 mN. In water (ε = 80), what is the force (μN)? (1 mN = 1000 μN)
7.5
3
What is φ at 0.9 m from q = 8 nC (V)? (k = 9·10⁹)
80
4
A charge q = 10 nC moves from a 300 V point to a 100 V point. What is the work of the field (μJ)? (nC·V = nJ)
2
5
Why is a lightning rod pointed?
At a point the charge density and E are large, the air ionises and the charge drains away safely.