I have two solenoids, one operate at 220v 1Amp (220watt power) and other at 12v 1Amp (12watt power). According to Magnetic field strength formula B= μ0nI, their B values should be same, but actually not. Can anyone tell me how this formula should be modified keeping both current and voltage in consideration?
Hi Shamoon Al Islam ,
the correct formula for a long coil is B = μ0 n I / len with number of turns n and length of solenoid len resp. number of turns per length n / len (with arbitrary len). The magnetic flux density does not depend on the voltage supplied to the solenoid. So, if both soleniods have the same number of turns per length, the field strength should be the same indeed at the same current.
However, I doubt that they have the same number of turns per length.
Your data look as if your solenoids are driven by DC because you calculate active power (in W) = voltage times current. If so, the ratio of the resistances would be R220 / R12 = 18.3, which can be accomplished by using a wire 4.3 times longer and with a cross-section area 1/4.3 times smaller for the 220V coil as compared to the 12V coil, resulting in n220 / n12 = 4.3.
I suspect that it is indeed AC, and that 220 VA and 12 VA is the apparent power. If so, if the impedance is mainly due to inductance L, and if both soleniods have similar cores, the ratio of the inductances L220 / L12 is about 18.3, and the ratio of the number of turns is the squareroot of this, n220 / n12 = 4.3.
In both cases, DC as well as AC, the magnetic field of the solenoid for 220 V will be about 4.3 times stronger than that of the other soleniod, provided the currents are the same.
Hi Sir @Joerg Fricke, thank you so much for clear and comprehensive answer. I got my answer. Many thanks.
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