Properties of Magnets
In this article, we will be sharing about the properties of magnets and how to determine whether a metal is magnetic or not.
Recently, a P4 student asked one of our teachers for help on a question on the properties of magnets.
The question is as follows:
Alan tried to make an electromagnet using the set-up as shown below.
a) What will happen to the iron pins when the switch is closed?
b) Will the same observation in (a) be observed when the steel rod is changed to a copper rod? Explain your answer.
To answer this question, let’s first understand what magnets are and their properties.
1. Magnets attracts magnetic materials.
A magnet is a material or an object that produces a magnetic field. A magnetic field (Figure 1) is invisible but is able to pull any magnetic material, such as iron, to the magnet itself, which is known as attraction. On the other hand, the magnetic field also can push away other magnets when their like poles are facing each other, which is known as repulsion. Hence, the unique property used to identify if an unknown object is a magnet or not is through the presence of repulsion between the unknown object and a magnet. If both repels each other, then the object would be a magnet too. However, if the object is attracted to both ends of a magnet, then the object is magnetic!
2. Magnets do not attract non-magnetic materials.
The magnetic field around the magnet does not interact with a non-magnetic object. Hence, there is no interaction (no attraction or repulsion) when a non-magnetic object placed near a magnet and the non-magnetic material does not move at all.
3. Magnetic materials can be magnetised into a temporary magnet.
A magnetic material can be magnetised or made into a temporary magnet by two methods: stroking method and electrical method (Figure 2).
The stroking method requires the same pole of a permanent magnet to be stroked along the magnetic material in one direction for many times. The greater the number of strokes, the greater the magnetic strength of the temporary magnet.
The electrical method requires a power source (usually a battery) to be connected to its two terminals (positive and negative) of the battery using wires. The wire must be coiled around the magnetic material into a temporary magnet, known as an electromagnet. The greater the number of coils around the magnetic material, the greater the magnetic strength of the electromagnet. Magnetic strength of an electromagnet can also be increased by increasing the number of batteries to allow more electric current to flow through the wire.
Now that we have done our recap on magnets, let’s go back the questions.
a) What will happen to the iron pins when the switch is closed?
The iron pins will be attracted to the steel rod.
Iron pins are magnetic, as we know objects that are made of iron, steel, nickel and cobalt (the 4 magnetic materials)can be attracted to a magnet, or in this case, an electromagnet/ temporary magnet. Hence, the iron pin will be attracted to the steel rod, which was magnetised into an electromagnet, when the switch is closed and the electric current can flow through the wire in a closed electric circuit.
b) Will the same observation in (a) be observed when the steel rod is changed to a copper rod? Explain your answer.
No. Copper is a non-magnetic material and the copper rod cannot be magnetised into a an electromagnet to attract the iron pins. Hence, the iron pins cannot be attracted to the copper rod.
First, the non-magnetic material, copper, is commonly confused with the magnetic material, cobalt since both starts with the same letter “C”. Hence, this question addresses this misconception and students should be careful to read the question properly before answering the question.
Second, it is false to assume that all metals are magnetic. There are only 4 metals which are magnetic, adn they are iron, steel, nickel and cobalt. Other metals, such as aluminium, silver, gold and copper are non-magnetic and cannot be magnetised into an electromagnet. Students tend to generalise the properties of metals as ALL metals are good conductors of electricity and heat and hence “All metals are magnetic” which is not true.
Third, how to know if a metal is magnetic? Simply place a magnet near the metal that you would like to test and if it is attracted to the magnet at any part, it is magnetic. If the metal is not attracted to the magnet, it is non-magnetic.
