This document discusses the transient current in an LR circuit with two inductors (L1 and L2) and a resistor connected to a 5V battery. It provides the equations for calculating the transient current in an LR circuit. It then calculates that for L1, the ratio of maximum to minimum current (Imax/Imin) is 8. Similarly, for L2 the ratio is 5. The total maximum current drawn from the battery is 40A and the minimum is 5A, giving a ratio of 8.

1. Physics Helpline
L K Satapathy
Transient Current QA 1
Transient Current in LR Circuit
L1
5V
L2R

2. Physics Helpline
L K Satapathy
Cells in ParallelTransient Current in LR Circuit
Question : The inductors L1 (inductance 1mH and resistance 3) and
L2 (inductance 2mH and resistance 4) and a resistor of resistance 12 are
connected across a 5V battery as shown in the figure.
Answer :
The circuit is switched on at time t = 0. The
ratio of the maximum to the minimum current
( I max / I min ) drawn from the battery is
(a) 3 (b) 5 (c) 7 (d) 8
In a LR circuit connected to DC voltage V , current at any instant is given by
R L
V.
1
R t
LVI e
R
 
  
 
min
max
0 [ 0]
& [ ]
I at t
VI as t
R
  
  
L1
5V
L2R
Transient Current QA 1

3. Physics Helpline
L K Satapathy
Cells in ParallelTransient Current in LR Circuit
(i) For ( L1 , R1 ) :
5 [ ]
12R
VI A const
R
 
Correct option = (d)
max
min
40 5 8
12 12I
[ ]ns
I
A  
L1
5V
L2
R
R1 R2
min max
1
50 & . . . (1)
3
VI I A
R
  
(ii) For ( L2 , R2 ) :
min max
2
50 & . . . (2)
4
VI I A
R
  
(iii) For the resistance R = 12 :
 Maximum current from source max
5 5 5 20 15 5 40
3 4 12 12 12
I A     
& Minimum current from source min
5 50 0
12 12
I A   
Transient Current QA 1

4. Physics Helpline
L K Satapathy
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