Generally, we see when we put iron nails at some distance to the magnet, it gets attracted towards it. Why is that so? We see that certain materials have the capability to attract materials towards themselves. The materials are attracted to the field around the magnet known as the magnetic field. Like due to electric charge producing an electric field also a magnet produces a magnetic field around it. The magnetic field is also created around the wire-carrying current.
What is a Magnet?
This is a piece of metal that attracts certain kinds of materials toward itself. There is a certain region of space around the magnet within which the magnetic effects can be felt. So if an iron nail is situated in that magnetic field, it will experience an attraction and if it is far beyond that magnetic field then it will not be attracted. A bar magnet is a form of a magnet whose shape is rectangular and has a magnetic field.
The north pole and the South pole are the two poles in a magnet. A field is created around the magnet. If we put the South pole of any magnet together with the South pole of another one, they repel each other. That means the like poles repel one another. Similarly, the South and North poles will attract each other. That means that poles attract each other. There are three main types of magnets.
- Temporary magnets in which when a magnetic field is removed then the object loses magnetic effects.
- Permanent magnets do not lose magnetic effects easily after magnetization.
- Electromagnets are used when a strong magnet is required.
Not all materials are attracted by the magnet. Materials like plastics, glass, and rubber are not attracted to a magnet and are non-magnetic materials. Materials like nails, screws, rods, etc are attracted to a magnet and are magnetic materials.
What is a Magnetic Field?
There are some materials like magnets that tend to attract other materials. This attraction is due to a field around the magnet that attracts the materials which are placed at some distance from the magnet. Always a magnetic field is associated with magnets within which the materials feel the magnetic effects.
The magnetic field is the area all over the magnet within which objects feel the magnetic force. It has both magnitudes as well as directions. It is represented by B.
Fig:1 Magnetic field of lines
It is described by drawing the lines of a magnetic field. These are imaginary lines that can be drawn connecting the north to the south pole. The lines show the direction from N-pole to S-pole outside the bar magnet and S-pole to N-pole inside it. These lines don’t intersect one another. If we draw a tangent to a point on the lines, it gives the direction of the field along that point. The total number of field lines per unit area is described as the magnitude of the field.
Also, magnetic fields are generated by a moving charge. The area around a conductor in which current flows has a field that deflects the materials within it.
Fig:2 Magnetic field around a conductor
This rule is used for determining the magnetic field’s direction around a straight conductor which carries current. To understand this rule first we need to understand how a current produces a magnetic field.
Fig:3 Current flow through a conductor
In wire AB, the magnetic lines due to a current-carrying conductor form concentric circles, and the centers of these circles lie on the wire. As shown in the figure, we have a straight wire AB that passes through the horizontal cardboard sheet. The two ends of the wire AB are connected to a battery. When the switch is turned on then, the current passes through the wire AB, and it creates magnetic field lines around it, which are circular. A compass near a wire is used to find the direction of the magnetic field produced. Determine the direction of the magnetic field of a conductor given by this rule.
Fig:4 Right-hand rule
In the right-hand thumb rule, the thumb shows the current’s direction which is flowing through the wire and the e fingers show the direction of the magnetic field lines around this wire. It means a magnetic field is present around the wire in the form of a circular shape.
So we conclude that in the direction of the current flowing in the wire flows in the upward direction, then the magnetic field is anticlockwise and if the direction of the current flows in the downward direction, then the magnetic field is in the clockwise direction.
Experiment to Demonstrate the Effect of a Magnet on a Current-Carrying Wire
An experiment was performed in which if a straight wire carrying current and the magnetic compass needle were placed near the wire, it shows some deflection. So it gives two conclusions-
- When the current in a wire increases, it increases the magnitude of the field generated by the wire itself.
- When the distance of a point from the wire increases, it decreases the magnitude of the field due to the current flowing through the wire.
In 1820, the magnetic effect of a current was observed by Hans Christian Oersted.
Fig:5 Experimental set-up to show the effect of a magnet on a current-carrying wire
In an experiment, Oersted took a simple circuit and connected a battery in such a way that electric current flows through the circuit and he placed a compass needle near the circuit. Now he observed that the magnetic compass needle shows deflection when current passes through the wire. Again he took the same magnetic needle away from the wire. Now he observed that the deflection decreased even for the same amount of current passing through the wire.
So he concluded that the nearer the needle more the deflection. Also, he observed when increasing the amount of current through the circuit the deflection increased, similarly when decreasing the amount of current through the circuit the deflection decreased.
Magnets always have two poles. The area around the magnet in which magnetic force is experienced is known as the magnetic field. The force that can be felt within the area of the magnetic field is magnetic force. Also, a wire carrying an electric current behaves like a magnet. The direction of this current and magnetic field can be found by using the right-hand rule.
Q1. Write any two uses of magnets.
- In a compass to show the direction
- In motors
Q2. What do you understand by the term solenoid?
Ans. A cylindrical insulating body(whose length is greater than its diameter) that contains a coil of many circular turns of insulated copper wire is called a solenoid.
Q3. Is it necessary for the magnetic field to touch the materials to attract them?
Ans. No. Magnetism works at a distance which defines that a magnet does not need to be touching an object for its attraction.
Q4. In a magnetic field, the conductor experiences a force due to the magnetic field. State the factors on which the direction of the force depends.
- Direction of current passing through a conductor.
- Direction of the field is created through a conductor.
Q5. What is the limit of the strongest magnetic field?
Ans. There is no fundamental limit on magnetic field strength.