Magnetic Effect of Current: In Straight, Curved Conductor

Before knowing about the magnetic effect of current, let’s understand how a magnetic field is created. Magnetism and Electricity are two sides of the same coin. Both are related to each other. Electric current creates a magnetic field. Similarly, a magnetic field creates a current. Both magnetism and electricity complement each other. 

The efforts of scientists like Faraday Oersted in establishing this relationship is something we have to be thankful for. We also use this effect in our daily lives in the form of many machines. Let us see the magnetic effect of electric current and how this is used in many applications.

Magnetic Field Definition

A magnet is an object that has the property to attract and repel another magnet and to attract certain metals such as iron, cobalt, and nickel. It also aligns itself in the North-South direction when suspendedly.

Study About Electricity and Magnetism

A magnet has an invisible field around it. It is a region in space surrounding a magnet where the magnet has an influence. If an iron piece comes within this field, it gets attracted. The field exists within the body of the magnet also. A similar kind of field can also be observed around a current-carrying conductor. The magnetic field is the region around a magnet or current element in which magnetic effects can be observed.

Properties of a magnetic field are:

1. Magnetic field lines emerge out of the north pole and enter through the south pole.
2. The field lines do not intersect or cross each other.
3. The field lines are in a closed loop, meaning that they exist inside the body of the magnet also.
4. Magnetic strength is more where the field lines are crowded. It is more at the poles.

What is the Magnetic Effect of Electric Current?

The magnetic effect of electric current is the phenomenon in which a current-carrying conductor creates a magnetic field around it.

Hans Christian Oersted, a scientist in the \({\rm{1}}{{\rm{9}}^{{\rm{th}}}}\) century, first observed the phenomenon where electric current creates a magnetic field. He noticed that a magnetic compass needle is deflected when kept near a current-carrying wire. The current creates a magnetic field around the conductor in the form of concentric circles.

Oersted’s Experiment to Verify Magnetic Effect of Electric Current

1. Connect a circuit with a battery cell and a switch to a straight conductor.
2. Place a compass near the straight conductor.
3. When the switch is off, the compass points to the north-south direction.
4. Turn on the switch to pass the current through the circuit.
5. We can observe that the needle of the compass deflects.
6. Move the compass closer to the conductor. It deflects more. Move it away, and its deflection is less.
7. Switch off the current. We can see that the compass reverts to its north-south direction.
8. This shows that the current-carrying conductor creates a new magnetic field around it to influence the compass.

Magnetic Field due to a Straight Conductor

We will do a similar experiment as the above:

1. Pass the straight conductor through cardboard.
2. Keep the straight conductor vertical.
3. Sprinkle some iron filings on the cardboard.
4. Switch on the current and gently tap on the cardboard.
5. We can observe that the iron filings arrange themselves in concentric circles around the conductor. These circles represent the field lines created by the current.
6. Place a compass on the board to note the direction of the field.
7. Reverse the direction of the current. We can see that the compass also reverses its direction of deflection.

The direction of the field around a current-carrying conductor can be found using Maxwell’s right-hand thumb rule.

Imagine holding the conductor in your right hand such that the thumb points to the current direction. Then the direction of the curl of the fingers gives the direction of the magnetic field.

Ampere’s swimming rule

If a man swims along the current-carrying wire with his face always facing the magnetic needle and the current entering his feet  and leaving his head, then the north pole of the magnetic needle will always get deflected towards the swimmer’s left hand.

Magnetic Field due to Current Through a Circular Loop

Now let us bend the conductor into a circular loop and pass it through cardboard.

1. Sprinkle iron filings on the board.
2. Pass current through the loop and gently tap the board.
3. We can see that the iron filings arrange themselves in concentric circles near the conductor.
4. At the centre of the loop, the filings are in a straight line.

We can apply the right-hand thumb rule to find the direction of the field. On the side of the loop where the current is going up, the field lines are anti-clockwise. On the other side, where the current is downwards, the field is clockwise. When the field lines of both parts of the loop approach each other, the lines become straight.

Magnetic Field due to a Solenoid

We saw that the magnetic field at the centre of a circular loop is a straight line. If we wind a conductor in many such loops in the form of a coil, it is called a solenoid. A solenoid is a coil of wire with many turns wound in the form of a cylinder.

Current is passed from one end of the solenoid to the other. Then the magnetic field due to each turn adds up to form a straight field through the centre of this cylinder. So, the solenoid behaves like a bar magnet. The strength of this field is increased by winding the solenoid over a soft iron core. An electromagnet is formed by this method.

We can find the direction of the field by the right-hand rule. For example, if we hold the solenoid such that the fingers point to the current direction, the thumb points towards the north of this field.

Factors that Determine the Strength of a Field due to a Solenoid

The strength of the magnetic field \((B)\) produced by a solenoid depends on –

1. The number of turns in the coil per unit length. The higher the number of turns, the stronger the field is.

\(B \propto \frac{N}{L}\)

2. The strength of current through the coil.

\(B \propto I\)

3. The nature of the material used as core.

We have seen that a current-carrying conductor creates a magnetic field around it. Let us see what happens when we place such a conductor in another magnetic field.

Force on a Current-Carrying Conductor in a Magnetic Field

Andre Marie Ampere, a French scientist, conducted an experiment to show that a current-carrying conductor experiences a force when placed in another magnetic field.

When a straight current-carrying conductor is placed perpendicular to a magnetic field, it experiences a force that moves it in a direction perpendicular to both that of the current and the field.

Fleming’s Left-Hand Rule to find the Direction of Force

The direction of movement of the conductor depends on:

1. The direction of the current
2. The direction of the magnetic field

The three directions are perpendicular to each other. The direction of movement of the conductor can be found using Fleming’s left-hand rule.

If we hold the left hand such that the thumb, forefinger, and the middle finger are perpendicular to each other, then –

1. if the forefinger points in the field direction,
2. if the middle finger points in the current direction,
3. then the thumb points the direction of movement of the conductor.

Application of Force on a Current-Carrying Conductor

An electric motor is the most common application of the magnetic effect of current. A motor is a rotating device that converts electrical energy to mechanical energy.

To explain it in simple words, a rectangular coil placed in magnetic field experiences equal and opposite forces at both sides. This makes the coil rotate. In addition, there is an arrangement at the ends called split rings to ensure the current direction in the sides is not changed. This keeps the coil rotating continuously.

Solved Example

Q.1. A straight conductor is carrying current and lying horizontal such that the direction of the current is from east to west. What is the direction of the magnetic field due to it, at a point lying just above the conductor?
Ans: From the right-hand thumb rule, if we imagine holding the wire such that the thumb pointing in the current direction, the curled fingers gives us the direction of the field. So the direction of the field at the given point is from south to north.

Summary

This article shows how electric current creates a magnetic field around the conductor carrying it. We saw how the shape of the conductor decides the shape of the magnetic field lines, as in the case of a straight conductor, at the centre of a single loop circular wire, or inside a cylindrical coil, called a solenoid. This inter-relation between electric current and magnetic field has been put to good use in various devices we use in our everyday lives, from electromagnets to motors, generators, to transformers.

FAQs

Q.1. When using Fleming’s left-hand rule, what direction is signified by the forefinger?
Ans: The forefinger signifies the direction of the magnetic field.

Q.2. In a horizontal circular loop, if the magnetic field points upwards, what is the current direction?
Ans: Upward magnetic field in a horizontal circular loop means that current is in anti-clockwise direction in the loop.

Q.3. When current flows down a straight vertical conductor, what direction is the field?
Ans: Right-hand rule tells that when the thumb (current) points downwards, the fingers (field) point in the clockwise direction.

Q.4. Why are split rings used in an electric motor?
Ans: Split rings ensure that the current direction in the coil is always in the same direction for continuous rotation.

We hope you find this article on the Magnetic Effect of Current helpful. In case of any queries, you can reach back to us in the comments section, and we will try to solve them.