The student forgot to divide by the time which would yield 5 m/s/s. (C)
Explanation:
(a) We have,
Length of solenoid, l = 55 cm = 0.55 m
Diameter of the solenoid, d = 10 cm
Radius, r = 5 cm = 0.05 m
Number of loops in the solenoid is 1000.
(a) The self inductance in the solenoid is given by :

A is area

(b) The energy stored in the inductor is given by :

Hence, this is the required solution.
Answer:
A
Explanation:
The figure shows the electric field produced by a spherical charge distribution - this is a radial field, whose strength decreases as the inverse of the square of the distance from the centre of the charge:

More precisely, the strength of the field at a distance r from the centre of the sphere is

where k is the Coulomb's constant and Q is the charge on the sphere.
From the equation, we see that the field strength decreases as we move away from the sphere: therefore, the strength is maximum for the point closest to the sphere, which is point A.
This can also be seen from the density of field lines: in fact, the closer the field lines, the stronger the field. Point A is the point where the lines have highest density, therefore it is also the point where the field is strongest.