Answer:
The winding density of the solenoid, n = 104 turns/m
Step-by-step explanation:
Given that,
Length of the solenoid, l = 0.7 m
Radius of the circular cross section, r = 5 cm = 0.05 m
Energy stored in the solenoid,

Current, I = 0.4 A
To find,
The winding density of the solenoid.
Solution,
The expression for the energy stored in the solenoid is given by :

Where
L is the self inductance of the solenoid

n is the winding density of the solenoid


n = 104 turns/m
So, the winding density of the solenoid is 104 turns/m