MORE ON ELECTRICITY AND MAGNETISM
After reading this section you will be able to do the following:
- Explain what a galvanometer in and how it is used.
- Begin to discuss how magnetism can be used to create electrical current.
In this demonstration you will use an instrument called a galvanometer. It is an instrument with a bar of iron wrapped with an electrical wire, and a magnet. It detects electrical current. If a wire is connected to this instrument, it can detect if electricity is flowing through the wire. If there is no current through the wire, the needle will move to the left. Similarly, if there is a current flowing through the wire, the needle will move towards the right of the scale. This demonstration should help to give you an idea of the relationship between magnetism and electricity.
- What happens to the galvanometer needle when the magnetic lines of force from the magnet interact with the electrical wire?
- When the galvanometer needle moves to the right, what does it tell you is happening in the wire?
- Why does the galvanometer needle return to zero when the magnet stops moving?
If electricity produces magnetism, can magnets produce electricity?
What you have just discovered in this experiment is that electricity can be generated by moving a wire through a magnetic field. This process is called electromagnetic induction. When an electrical wire cuts across magnetic lines of force, a current is produced in the wire. We know this because the current is detected by watching the needle on a galvanometer, which is an instrument that can measure electric current in wires. The same result is obtained when a magnet is moved in and out of coils of wire. It does not matter if the magnet is moved or if the coils of wire are moved. The important thing is that there is motion within the magnetic field, and that the magnetic lines of force are cut.
Why is electromagnetic induction important to us?
The discovery of electromagnetic induction is very important in our lives because it is the principle by which electric generators can make electricity. Through the use of magnets, a generator can convert mechanical energy to electrical energy and provide electricity that we need for so many things. Remember that energy is the ability to do work and that mechanical energy is the energy caused by moving objects. For example, when you move your legs to peddle a bicycle, you cause energy that moves the bicycle wheels and runs the bicycle. When a rushing wave of water hits a boat and turns it over, the moving water causes the energy that moves the boat to overturn it. When there is a way to turn this moving energy into electricity that can light a light bulb, we can get light in our home.
How does a magnet help a generator convert mechanical energy into electrical energy?
A generator works very much the same as you saw in the experiment. Inside a generator is a magnet, some electrical wire, and a source of mechanical energy. The mechanical energy moves the wire into the magnetic field of the magnet so that the wire cuts through the magnetic lines of force. As a result, electric current is produced. Electric generators can come in all sizes. Some electric generators are very big and contain huge magnets so they can produce a lot of electricity. On the other hand, some generators contain small magnets and are small enough to hold in your hand. These small generators may produce only enough electricity to light one small light bulb.