The Strength of an Electromagnet APP This has been part of the KS3 syllabus since the inception of the National Curriculum. The section on magnetism in Y8 has included a review of permanent magnetism and its laws. 1.A permanent magnet has two poles- North and South. 2.The region around a magnet where it can attract magnetic materials is called a magnetic field. This is a three dimensional region and it is strongest near the poles. 3.Permanent magnets have uses in the compass, door catch, fridge door seal etc N S

The Strength of an Electromagnet A permanent magnet cannot be switched on or off nor can its strength be changed so a better magnet is needed where control of the strength is essential. Oersted discovered that when a wire carries an electric current it forms a magnetic field around it. This field is stronger if : a) the current is greater b) the wire is coiled into a shape called a solenoid c) a core of iron is placed inside the solenoid Electromagnet is OFF ‘soft’ iron core Coil or ‘solenoid’ with turns of insulated wire Switch is open so no current flows N

The Strength of an Electromagnet The theory of magnetism in a metal like iron says that there are small areas of magnetism inside the metal called DOMAINS. Normally, these are randomly arranged so their magnetism cancels out. If a magnetic field surrounds the metal, the domains can be aligned in the SAME DIRECTION so their magnetism adds up until it reaches a maximum power. Switch is closed so current flows The solenoid magnetises the iron so it will deflect a compass Electromagnet is ON N

The Strength of an Electromagnet If the core is shaped into a horseshoe, the strong field near each pole can be used to lift an object such as a nail. This is the familiar shape of an electromagnet. If some masses are hung from the nail, then the strength of the electromagnet can be tested. ‘turns’ of insulated wire Iron ‘C’ core 2 volt power pack Iron nail Mass hanger Slotted masses 10g, 20g, 100g

Equipment for the experiment ‘C’ core Length of insulated wire Iron nail Mass hanger 2 volt power pack Set of 10g, 20g and 100g masses. Retort stand, clamp and boss. Clamp to hold the stand secure. Prepared table for your results Electric balance.

In this investigation, these factors stay the same. The total length of insulated wire. The power pack so the current stays the same. The nail and the mass hanger (you must weigh them both first) The iron core The factor that you change is the number of turns of insulated wire. Start with the least number that will hold the nail (at least 12), record the mass Then see if it will hold the mass hanger, if it does record that mass. ‘turns’ of insulated wire Iron ‘C’ core 2 volt power pack Iron nail Mass hanger Slotted masses 10g, 20g, 100g

No. of turns Mass 1 (g) Mass 2 (g) Mass 3 (g) Average mass (g)

The Strength of an Electromagnet Now increase the number of turns by 2. See if it will hold any more masses. Write your results in a table. Keep going for at least another 6 results. You must also repeat your results. Watch for a pattern. ‘turns’ of insulated wire Iron ‘C’ core 2 volt power pack Iron nail Mass hanger Slotted masses 10g, 20g, 100g

Average No. of turns Mass it will hold / g 12 14 16 18 20 22 Plot the number of turns on the x-axis and the mass held (g) on the y-axis as a point graph. Average No. of turns Mass it will hold / g 12 14 16 18 20 22 50 45 40 35 30 Mass held (g) 25 20 15 10 5 10 20 30 40 50 60 70 80 90 Number of coils