1 Can you think of an electromagnet that is capable of producing stronger magnetic field than the magnetic field produced by any permanent magnet?
2 what is known as the range of an ammeter
3 what will happen if the thick wire is kept horizontal instead of vertical ( in activity 13.5 ncert )
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Which would generate a stronger magnetic field: an electromagnet with more turns and thinner wire, or an electromagnet with fewer turns and thicker wire?
MMF (magnetomotive force) of a coil of wire is measured in Ampere-turns by the SI units. It can be converted to the CGS (centimeter gram second) unit of Gauss by the appropriate conversion factor.
Note that it is A*t, or amperes multiplied by the number of turns.[1]
It depends on the current and voltage available. One single turn of a massive copper wire with 100 A through it: 100 At of MMF. One hundred turns of wire filling the same space but with only 1 A: 100 At of MMF. Put a thousand turns of wire on the coil, and it only takes 100 mA to get 100 At.
But due to wire resistance, it will take a higher voltage to push 1 A through a thinner wire. So you must consider your source of power when deciding between wire thickness and number of turns.
There is another issue, that of packing efficiency and insulation. One very thick rectangular cross section turn of wire will have more copper in it than many turns of round wire with insulation. This is why the insulation on magnet wire is a very thin coating of enamel.
Because we are looking at the cross section of the wire, we will look up something called “circle packing”.[2]
This graphic shows a circular wire as the baseline. If a square or rectangular wire were used in the first (single turn) case, the difference in packing efficiency is even greater.
However, you may also use something called Litz wire. This is essentially a stranded wire with each wire separately insulated. Smaller strands mean greater packing efficiency without requiring the higher voltage that more turns of thinner wire would require. It is even possible to get Litz wire preformed into a square or hexagonal cross section.[3]
Rectangular, flat, or custom shapes:[4]
So you are thinking, forget packing efficiency and Litz wire, just use a single turn of 0000 gauge wire with 100A through it. But you have to get the power there. Say one turn around your coil is 10cm. If you use 0000 gauge wire to bring power to the electromagnet, for every 10cm of wire you are losing just as much as you are losing in the single turn. So you need wire MUCH larger to avoid creating a terribly low efficiency. Converting incoming 50 or 60Hz AC into a 100A low voltage power supply is fraught with difficulties, not the least of which is the necessity of a fairly complex switch mode converter to avoid several volts of loss through diodes at such high current levels.
Simpler to choose a trade-off that requires more voltage against the wire resistance, but much less current due to more turns.
hope it helpss
MMF (magnetomotive force) of a coil of wire is measured in Ampere-turns by the SI units. It can be converted to the CGS (centimeter gram second) unit of Gauss by the appropriate conversion factor.
Note that it is A*t, or amperes multiplied by the number of turns.[1]
It depends on the current and voltage available. One single turn of a massive copper wire with 100 A through it: 100 At of MMF. One hundred turns of wire filling the same space but with only 1 A: 100 At of MMF. Put a thousand turns of wire on the coil, and it only takes 100 mA to get 100 At.
But due to wire resistance, it will take a higher voltage to push 1 A through a thinner wire. So you must consider your source of power when deciding between wire thickness and number of turns.
There is another issue, that of packing efficiency and insulation. One very thick rectangular cross section turn of wire will have more copper in it than many turns of round wire with insulation. This is why the insulation on magnet wire is a very thin coating of enamel.
Because we are looking at the cross section of the wire, we will look up something called “circle packing”.[2]
This graphic shows a circular wire as the baseline. If a square or rectangular wire were used in the first (single turn) case, the difference in packing efficiency is even greater.
However, you may also use something called Litz wire. This is essentially a stranded wire with each wire separately insulated. Smaller strands mean greater packing efficiency without requiring the higher voltage that more turns of thinner wire would require. It is even possible to get Litz wire preformed into a square or hexagonal cross section.[3]
Rectangular, flat, or custom shapes:[4]
So you are thinking, forget packing efficiency and Litz wire, just use a single turn of 0000 gauge wire with 100A through it. But you have to get the power there. Say one turn around your coil is 10cm. If you use 0000 gauge wire to bring power to the electromagnet, for every 10cm of wire you are losing just as much as you are losing in the single turn. So you need wire MUCH larger to avoid creating a terribly low efficiency. Converting incoming 50 or 60Hz AC into a 100A low voltage power supply is fraught with difficulties, not the least of which is the necessity of a fairly complex switch mode converter to avoid several volts of loss through diodes at such high current levels.
Simpler to choose a trade-off that requires more voltage against the wire resistance, but much less current due to more turns.
hope it helpss
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