Investigation into the Strength of an Electromagnet

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George Maund

Investigation into the Strength of an Electromagnet

Planning Experimental Procedure

When electric current is passed through a wire a magnetic field is created. If you wind the wire around an iron core, then you have an electromagnet. They have North and South poles just like normal magnets, but it does have some differences – if you switch off the current, the magnetic field is lost, and the strength of the magnetic field can be altered by either changing the number of coils around the core, or by changing the current.

I intend to measure the strength of an electromagnet – a magnet consisting of an iron core with plastic-coated wire rapped around. When current is applied through the wire, the iron core becomes magnetic – and I intend to test the effect of varying the current. The factors that will have an affect on the quantity I’m investigating include room temperature, material of core, number of coils around the core – I intend to keep all of these constant. The factor I intend to vary in my investigation (independent variable) will be current – the current flowing through the coils of the electromagnet. I have chosen this as I think it will be the easiest to investigate and carry out. The other variables (number of coils) will be kept constant so as to give valuable and worthwhile results.

Prediction

My prediction is that the amount of current passed through the wire will be directly proportional to the strength of the electromagnetic iron core.

Scientific Explanation of my prediction

The scientific explanation of this is that within electromagnets there are domains (see below), which are very small magnets within the iron core (the smallest are each 1/1000th of a mm). When no current is passing through the coils, the domains all face in different directions, so the core is not magnetic. However when current is applied through the coils, the domains begin to face in the same direction, thus making the core magnetic. The more domains are turned, the easier it is for other surrounding domains to be turned by the coils. This is why the predicted graph (below right) takes a while to pick up, then after going straight, trails off – the trailing off is where all the domains have been turned, so the iron core is at maximum magnetic capability. The same principle applies when the number of coils is increased – there is a further spread of the current, so more domains are turned, and the more domains there are, the stronger the magnetic field.

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Explanation of Domain Theory

Here we see a close up of the domains, the smallest possible magnets (1/1000th of a mm), which are randomly facing different directions. No current is being applied.

Here the domains are beginning to line up inside the iron core. The amount of current applied is slowly increasing….

…And as it increases, more and more domains become turned, until eventually all have been turned and the magnet is at maximum strength.

Apparatus:                Newtonmetre        s*

                        Stand

Clamp

                        Ammeter

                        Variable resistor

                        Mains supply

Electromagnet:        Iron core

Wire coil

*I ...

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