Magnetic field in the coil

[Murugesh_89]

Hi,
If a coil which has a number of turns = 400, resistance = 50 is connected across the 5V supply, then 100mA of current flows through the coil and it will create a magnetic field (M1).

If we increase the number of turns to 480, which will increase the resistance to 60, is connected across the same 5V source then a current of 83mA is flowing through the coil which will create a magnetic field (M2).

Since the number of turns and hence the inductance of coil is higher in M2 than M1, will the M2 is higher than M1? or
since the current through the coil is greater in M1 than M2, will the M1 is higher than M2?

Please give me clear explanation...

 

[slanina]

Hi,
If a coil which has a number of turns = 400, resistance = 50 is connected across the 5V supply, then 100mA of current flows through the coil and it will create a magnetic field (M1).

If we increase the number of turns to 480, which will increase the resistance to 60, is connected across the same 5V source then a current of 83mA is flowing through the coil which will create a magnetic field (M2).

Since the number of turns and hence the inductance of coil is higher in M2 than M1, will the M2 is higher than M1? or
since the current through the coil is greater in M1 than M2, will the M1 is higher than M2?

Please give me clear explanation...

In first case you have 400 turns * 0.1 Amperes = 40 ampere turns.
In second case you have 480 turns * 0.083 Amperes = 39.84 amperes.

They should be about equal.

To increase magnetic field, you should increase wire diameters (to reduce resistance which would automatically increase the current) or introduce an adjustable constant current source which would be able to drive more current through the coil, in which case there should also be sufficient voltage (V=I*R). You can play with lab power supplies.

Bear in mind that a thin wire can become hot if you drive too much current through it.

 

[Murugesh_89]

In the same case as previously posted if i give same 5 voltage to a coil but as pulses to the same coil now.

How the duty cycle will play in deciding the magnetic field strength?

I mean out of these three cases below which one have higher magnetic field or force of attraction? Here you consider that i will give 5 pulses with this duration.
1. On time = 100 ms and Off time = 400ms
2. On time = 250 ms and Off time = 250ms
3. On time = 400 ms and Off time = 100ms

 

[slanina]

In the same case as previously posted if i give same 5 voltage to a coil but as pulses to the same coil now.

How the duty cycle will play in deciding the magnetic field strength?

I mean out of these three cases below which one have higher magnetic field or force of attraction? Here you consider that i will give 5 pulses with this duration.
1. On time = 100 ms and Off time = 400ms
2. On time = 250 ms and Off time = 250ms
3. On time = 400 ms and Off time = 100ms

First, magnetic field is of the same strength the moment coil is on and it will always attract with the same force. So with pulsing you have to look at its performance over the time.
Second, what kind of coil is it? And what core do you use?

What are you trying to do anyway?

 

[Venkadesh_M]

Hi magnetic flux is a Instantaneous quantity So it will be there as the MMF present there... If you are just considering about the attraction specimen then you don need worry about anything and just get avg, and also maintain the pulsing frequency higher to maintain the avg attarction force constant and also now you have to consider the inductance of the coil because now you are introducing AC component....

 

[BradtheRad]

In the same case as previously posted if i give same 5 voltage to a coil but as pulses to the same coil now.

How the duty cycle will play in deciding the magnetic field strength?

I mean out of these three cases below which one have higher magnetic field or force of attraction? Here you consider that i will give 5 pulses with this duration.
1. On time = 100 ms and Off time = 400ms
2. On time = 250 ms and Off time = 250ms
3. On time = 400 ms and Off time = 100ms

The greater the current going through the coil, the stronger the flux field. Hence the longer the duty cycle, the more the flux field can build. It also has less time to collapse, with the result that the field's average intensity is greater.

This assumes a sufficiently high frequency of operation.

 

[chuckey]

Hold on Guys, you have forgotten that the current rises exponentially in an inductor ( T = L/R), if the pulse is short compared to this time constant, then very little current flows, The pulse has to be on for 4-5 times T, for the full current to flow.
Frank