Question

What is the coil current 2ms after being connected to the supply if a coil of inductance 0.5H and resistance 500`Omega` is connected across a 250V DC supply? (The time constant T of the circuit is 1ms).

Answer 1

For an LR Series circuit as shown in the figure above, the expression for the current `I` is given as

`I(t)=E/R(1-e^(-t/tau))`
where time constant `tau= L/R` and `E/R` represents the final steady state current in the circuit.

Inserting given values we get

`I_"(2 ms)"=250/500(1-e^(-2/1))`
`=>I_"(2 ms)"=0.43\ A`

.-.-.-.-.-.-

We can verify that `tau=0.5/500=0.001\ s`, as given