Importance
The chapter on Magnetic effects of electric current is assigned a weightage of \(6\) marks, highlighting its significance in the overall curriculum. Understanding this chapter will enhance the knowledge of the relationship between electricity and magnetism, especially how electric currents create magnetic fields.
Also to prepare effectively for related exam questions. It is essential to grasp the various types of concepts, laws and applications of magnetic effects. Focusing on these concepts will greatly benefit both academic performance and practical application in physics.
- Section A (\(1\) mark) - Three questions
- Section C (\(3\) mark) - One question
Learning outcomes
- Understand the Relationship: Explain the relationship between electric currents and magnetic fields, including the principles of electromagnetism.
- Apply the Right-Hand Rule: Use the right-hand rule to determine the direction of the magnetic field generated by a current-carrying conductor.
- Calculate Magnetic Field Strength: Calculate the magnetic field strength at a given distance from a straight current-carrying wire using the appropriate formula.
- Examine Electromagnets: Explain how electromagnets are created and their applications in real-world devices, such as motors and transformers.
Electricity is one form of energy involving the flow of electrons.
The nucleus includes,
- Protons - positively charged particles, and
- Neutrons - uncharged particles
The nucleus of an atom is enclosed by negatively charged particles known as electrons.
What could be the effects of electric current?
When current flows in a circuit, it shows various effects. The main effects are,
- Heating
- Chemical, and
- Magnetic effects
Electromagnetism:
In the 19th century, one of the leading scientist, Hans Christian Oersted, played an important role in understanding the concept of Electromagnetism.
In 1820, he accidentally found that a compass needle gets deflected when an electric current passed through a metallic wire placed nearby.
Through this observation, Oersted confirmed that electricity and magnetism were related phenomena. His research later produced technologies such as radio, television and fibre optics.
The unit of magnetic field strength is named after Oersted in his honour.
What is Electromagnetism?
Electromagnetism is a branch of physics. It deals with the study of electromagnetic force, a physical interaction between electrically charged particles.
The electromagnetic force is carried by electromagnetic fields comprised of electric and magnetic fields, responsible for electromagnetic radiation such as light.
The magnetic compass is a device that is used to locate the direction of a place.
It always rests in a north-south direction and is very helpful as a navigator in ships, submarines and aeroplanes.
A compass needle acts as a small bar magnet. we have observed that like poles repel, while unlike poles of magnets attract each other.
Working principle of Magnetic compass:
The magnetic compass works with the Earth’s magnetic field principle and shows the magnetic North and South. The magnetic compass has a magnetised needle, that can freely rotate in a horizontal plane. Such a magnetic needle tends to settle in the magnetic meridian.
What happens if we put a compass needle near a bar magnet?
Deflection of compass when it is brought near a bar magnet
We can see that the red portion inside the bar magnet and the needle represents the North pole. And, the grey and white portions represent the bar magnet's South pole and the needle.
You can observe that the North pole in the magnetic needle is always deflected towards the South pole of the bar magnet and vice-versa.
Why does a compass needle get deflected when brought near a bar magnet?
A compass needle gets deflected whenever a bar magnet is brought near to it. Because, a magnetic compass can be assumed as a pole, and the magnet creates a magnetic field.
If we place both a compass and the magnet at rest, the compass will be reflected in a direction and constant.
But if you move the magnet, it will alter the generated flux lines. Through this we can conclude that there is a change in direction or magnitude, and the needle gets deflected near a bar magnet.
We know that an electric current-carrying wire acts like a magnet.
Let us do the following activity to reinforce it.
Let us do the following activity to reinforce it.
Steps:
- Take a straight, thick copper wire and fix it between the point X and Y in an electric circuit, as shown in the below figure.
Electric circuit
- The wire XY is maintained perpendicular to the plane of the paper.
- Horizontally, place a small compass near this copper wire.
- Observe the position of its needle.
- Pass the current through the electric circuit inserting the key into the plug.
- Observe the change in the position of the compass needle.
Observation:
We observe that the needle is deflected.
What does it mean?
It means that the electric current flows through the copper wire have induced a magnetic effect.
Thus, we can state that electricity and magnetism are connected.
In the previous sections, we have learned that electromagnetic force is carried by electromagnetic fields that comprise electric and magnetic fields. In this session, we are going to learn about magnetic fields in detail.
A magnetic field is an area around moving electric charges, electric currents, or magnetic materials within which the force of magnetism acts.
It can be represented by "B", and the unit is Tesla.
Magnetic field lines
A moving charge in a magnetic field undergoes a force perpendicular to its velocity and the magnetic field.
Moving charge in a magnetic field
Magnetic fields are created by moving electric charges and the intrinsic magnetic moments of elementary particles connected with a fundamental quantum property, and spin of the particles.
Rotating magnetic fields are generally used in electromechanical applications such as electric motors and generators. The influence of magnetic fields in electric devices such as transformers is formulated and examined as magnetic circuits.
Magnetic field lines:
Magnetic field lines are a visual tool used to represent magnetic fields. They describe the direction of the magnetic force on a North monopole at any given position.
Properties of magnetic field lines:
- Magnetic field lines never intersect each other.
- The density of the field lines shows the strength of the field.
- Magnetic field lines always make closed-loops.
- Magnetic field lines always emerge from the north pole and terminate at the south pole.
Spray some iron filings evenly around the bar magnet, as shown in the below figure. You may use a salt sprinkler for this purpose.
Now, tap the board mildly.
Magnetic field shown by iron filings
Observation:
The iron filings organise themselves in a pattern, as shown in the below figure. The magnet exerts its impact in the area surrounding it. Therefore, the iron filings experience a force. The force thus exerted makes iron filings order in a pattern. The area surrounding a magnet (where the magnet's force can be recognised) has a magnetic field. The lines along which the iron filings arrange themselves denote magnetic field lines.
Activity to draw magnetic field lines by compass
Steps:
- To do this activity, take a small compass and a bar magnet.
- Using an adhesive material, locate the magnet on a sheet of white paper fixed on a drawing board.
- Mark the boundaries of the magnet.
- Locate the compass near the north pole of the bar magnet.
Position of the needles from north to the south pole
How does it act?
The south pole of the needle moves towards the north pole of the bar magnet. The north pole of the compass is pointed away from the north pole of the bar magnet.
Direction of the field produced
To find the direction of the field produced, let us do the activity in the following way,
- Locate the straight wire parallel to and over a compass needle.
- Plug the key in the circuit.
- Note the direction of deflection of the north pole of the needle. As shown in the figure, if the current flows from north to south, the compass needle's north pole will move towards the east.
Direction of the field produced when current reversed
- Next, replace the cell connections in the circuit as shown in the below figure.
- This would result in the change of the current direction through the copper wire, that is, from south to north.
- Note the change in the direction of deflection of the needle.
You will see that now the needle moves in the opposite direction, that is, towards the west [see the figure]. It means that the direction of the magnetic field produced by the electric current is also reversed.
Magnetic field around a wire
The above diagram shows the magnetic field around a wire when the wire has a current flowing in it.
The central arrow represents the direction of the current in the conductor. The circles are field lines, and the arrows show their direction on the lines. Similar to electric field lines, the greater the number of lines (or the closer they are together) in an area, the stronger the magnetic field. If there is no current, there will be no magnetic field.