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 )
4 You are provided with an iron strip and a bar magnet. How will you distinguish them?
5 How does a compass needle work?
6 Can an ordinary magnet be used as a compass?
7 In this experiment, it is advised to use a small compass needle. ( in activity 13.5 ncert )
8 What will happen if a small compass needle is replaced with a big size compass needle? ( in activity 13.5 ncert )
9 How magnetic field lines of a straight current carrying wire are different from the field lines of a bar magnet?
10 What affect you will notice on the pattern of field lines if you interchange a rheostat by the plug key in this experimental arrangement? ( in activity 13.5 ncert )
11 How can the direction of the magnetic field be determined? Suggest all possible methods.
Answers
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.
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”.