Answer:
the number of turns in the winding is 387 turns.
Step-by-step explanation:
Given;
radius of the solenoid, r = 0.12 m
cross sectional area of the solenoid, A = 20 x 10⁻⁴ m²
current flowing through the solenoid, I = 20 A
the energy of the flowing current, E = 0.1 J
The energy stored in solenoid is given as;

The number of turns in the winding is calculated as follows;

Therefore, the number of turns in the winding is 387 turns.