# how to find out current through inductor in DC circuit?

Discussion in 'Homework Help' started by vead, Aug 4, 2016.

1. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
Hello
I need help to understand the basic concepts of inductor. Suppose 1h inductor is connected across 10v battery. Inductor is non linear element it change the value of current over the time. How to find out current through inductor?

2. ### Ramussons Active Member

May 3, 2013
562
92
Any problem using a Ammeter or Millammeter?

Feb 5, 2010
3,847
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4. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
I can use the multimeter but I just want to find out using the formula.

5. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,968
1,135
E=10, L=1. Use the formula to find di/dt.

Nov 24, 2011
621
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7. ### DickCappels Moderator

Aug 21, 2008
2,766
667
You can use the formula for LR circuits. Use an ohmmeter to find the resistance of your inductor and use that value as R in the formula.

8. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
So I don't know time and I have find out the current. Should I have to suppose the time

9. ### DGElder Member

Apr 3, 2016
347
87
The current will rise linearlly at 10A per second, until the universe explodes. At least that is what would happen if you had ideal inductor and voltage source. Real components have resistance, use the tutorial math. You will need to know the source output resistance and inductor resistance to calculate the current.

Don't try hooking that up, you will pop a fuse or drain your battery.

Last edited: Aug 4, 2016
10. ### Alec_t AAC Fanatic!

Sep 17, 2013
5,968
1,135
di/dt means 'the rate of change of current with time'. If you found one (non-zero) value of the current that must have been at one specific time, unless the current had reached a value limited by the resistance of the inductor.

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11. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
given
V=10v, L=1h, di/dt=10A/s
Voltage drop across the inductor is
v=Ldi/dt
v=1*10=10v
Voltage drop across the 1h inductor is 10 volt
Still the current is unknown

12. ### crutschow Expert

Mar 14, 2008
13,481
3,368
If you can't understand what is being said to you then how can we help?

The current isn't unknow, you just haven't calculated it.
The current in an inductor continually increases with time after the application of a DC voltage according to (di = Vdt/ L).
This gives the increase in current with time.
To find the current at any point in time you multiple the time by V/L
Thus, in you example, at 5 seconds the current would be 5s * 10A/s = 50A
The maximum current in the inductor after a large period of time is limited by any resistance in the circuit and will settle at a value of V / R.

If you can't understand that, than I don't know what further can be said.

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13. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
Now I can understand and I can find out the energy stored in inductor
E=1/2Li*i
E=0.5*1*50*50
E=1250 joules

Power P=Li*di/dt
P=1*50*10
P=500W
Is this calculation is correct?

14. ### Papabravo Expert

Feb 24, 2006
10,340
1,850
That equation is not true when V and i have reached their steady state values. As you know, steady state means nothing is changing, and so di/dt will be zero for all future time and the value of L will be irrelevant, thus:

$P_L\;=\;i^{2} \times R_L\;=\;\left(\frac{V_L}{R_L} \right) ^2\times R_L$

Last edited: Aug 4, 2016
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15. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
Now I just connected the AC supply across 1h inductor
If the applied voltage is 10v AC with 60Hz signal than I am trying to find out current through inductor
Inductive reactance XL=2*3.14*f*L
XL=2*3.14*60*1
XL=377.11ohms
Now I know the Inductive reactance than I can calculate current through indctor
I=V/XL=10/377.1=0.0265A
I just wanted to know that how can we determine current through the inductor in AC and DC circuit
So again, please check my work and if there is any mistake tell me

16. ### DGElder Member

Apr 3, 2016
347
87
That is correct.

17. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
An inductor is NOT non-linear element.

What is your math background like? Have you seen any calculus yet? Do you understand exponentials and logarithms?

18. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
Power in AC circuit
P=i*i*XL
P=0.265*0.265*377.11
P=0.2648w
How to calculate energy in AC circuit

19. ### WBahn Moderator

Mar 31, 2012
18,085
4,917
What energy are you trying to calculate? There are different energy questions that could be asked.

20. ### vead Thread Starter Well-Known Member

Nov 24, 2011
621
8
OK my mistake
Resistor, capacitor and inductor are linear element
Diode transitor are non linear element