<h2>
Answer:</h2>
(a) 1860 Ω
(b) 0.16H
<h2>
Explanation:</h2>
This is an RL circuit as it contains an inductor with and inherent resistance.
The current, I, flowing through such circuit is given by;
I =
[1 -
] --------------(i)
Where;
E = emf of the circuit = 12.0V
R = Resistance of the inductor
L = inductance of the inductor
t = time taken for the flow of current
(a) After a long time, i.e t → ∞, the current becomes saturated (i.e maximum) and the value is 6.45mA.
At this time,
(from equation (i)) becomes 0 and current I, becomes;
I =
-------------------(ii)
Now substitute the value of E and I into equation (ii) as follows;
6.45 x 10⁻³= 
R = 
R = 1860Ω
Therefore, the resistance of the inductor is 1860 Ω
(b) To get the inductance L of the inductor, we substitute I = 4.86mA at time t = 0.725ms into equation (i) as follows;
4.86 x 10⁻³ =
[1 -
]
4.86 x 10⁻³ x 1860 = 12.0[1 -
]
0.7533 = [1 -
]
1 - 0.7533 =
0.2467 = 
Take the natural log of both sides
ln(0.2467) = -1860 x 0.00468 / L
-1.3996 = -8.7048 / L
L = -1.3996 / -8.7048
L = 0.16H
Therefore, the inductance of the inductor is 0.16H