Class 10 Science Notes

~6 min read

Magnetic Effects of Electric Current Class 10 Notes

This chapter is the physics of electricity's other face. It begins with magnetic fields and field lines, then builds up from a straight wire to a coil and a solenoid, which behaves like a bar magnet. It moves on to the force on a current-carrying conductor and Fleming's left hand rule, compares direct with alternating current, and closes with the domestic circuit, its fuse and earth wire.

Class:10Subject:ScienceUnit:IVCovers:CBSE 2024-25

6 Key Formulas

DWritten byDeep Narayan

UpdatedSeptember 2026

Key Concept Summary

State Fleming's left hand rule and explain how the direction of the north pole of a solenoid is decided.

Fleming's left hand rule gives the direction of the force on a current-carrying conductor placed in a magnetic field: stretch the left hand so that the thumb points along the direction of motion, the forefinger along the field from the north pole to the south pole, and the middle finger along the current, and the thumb then gives the direction of the force. For a solenoid, the end from which the current is seen to flow anticlockwise is the north pole, while the end from which it is seen to flow clockwise is the south pole. The field of a solenoid is stronger when it has more turns or a larger current, and inside the coil the field is uniform and directed along the axis.

Magnetic Field and Field Lines

A magnetic field is the region around a magnet in which a magnetic compass needle shows a deflection, and the direction of the field at any point is taken as the direction in which the north pole of a compass needle points when it is placed there.The field of a bar magnet is represented by a set of imaginary lines called magnetic field lines. These lines never intersect each other, and they are closest together where the field is strongest, which is near the poles, and farthest apart where the field is weak, which is around the middle of the magnet.

A magnetic field is the region in which a magnetic compass needle is deflected.
Field lines are imaginary lines used to represent the field, and no magnet is actually marked with them.
The direction of a field line at any point is the direction in which the north pole of a compass needle points there.
Field lines never cross or intersect each other, however crowded the field may be.
Field lines are closer together where the field is strong, as near the poles, and wider apart where it is weak.
Outside a bar magnet the field lines run from the north pole to the south pole, and inside the magnet they run from the south pole back to the north pole.

How field lines are described

A field line is a line drawn such that the tangent to it at any point gives the direction of the magnetic field at that point.The two properties the board always tests are that field lines never cross and that they are closer together where the field is stronger.Field lines are closed curves, so they run from the north pole to the south pole outside the magnet and return from the south to the north inside it.

Field of a Straight Current-Carrying Conductor

Oersted's observation, made long before the field of a magnet was studied in detail, is that a magnetic compass needle placed near a straight wire deflects whenever a current flows through the wire. This shows that a current produces a magnetic field, just as a magnet does.The field lines around a straight current-carrying conductor are concentric circles centred on the wire, and the plane of each circle is perpendicular to the wire. The strength of the field is greatest close to the wire and decreases as the distance from the wire increases, so the circles get farther apart further from the conductor.

A current-carrying conductor produces a magnetic field of its own, shown by the deflection of a compass needle near the wire.
The field lines around a straight conductor are concentric circles whose centres lie on the conductor.
The circles lie in planes perpendicular to the wire, and the field is strongest at the surface of the wire.
The field weakens as the distance from the conductor increases, so the circles grow farther apart.
The direction of the field is given by the right-hand thumb rule, and the fingers curl in the direction of the field lines.
Reversing the current reverses every field line, since the direction of the field depends on which way the current flows.

The right-hand thumb rule in words

Point the right thumb along the direction of the current in the wire, and the curl of the fingers gives the direction in which the magnetic field lines run.If the current is reversed, the whole pattern of circles turns over, so the direction of the field and the direction of the current are always linked.The field is never a property of the wire alone, since an uncharged wire with no current through it produces no magnetic field at all.

Field of a Coil and the Solenoid

Bending a straight conductor into a circular coil does not destroy the magnetic field but concentrates it, since the fields produced by the several turns of the coil act together at the centre. The field of a single circular loop is very weak, and it is for this reason that instruments and electromagnets use many turns.A solenoid is a coil of many turns wound closely on a cylindrical core, and it behaves exactly like a bar magnet, with a north pole at one end and a south pole at the other. The field inside a solenoid is nearly uniform and directed along its axis, and the field outside it is the same pattern as that of a bar magnet, so an iron nail placed inside a solenoid becomes magnetised and can pick up pins.

A single circular loop produces a magnetic field along the axis of the loop, and it is very weak.
A coil of many turns produces a much stronger field, because the field of each turn adds to that of the others.
A solenoid is a coil of wire wound on a cylindrical core, and it behaves like a bar magnet.
The field inside a solenoid is uniform and parallel to its axis, while outside it has the pattern of a bar magnet.
Face rule: the end from which the current is seen to flow anticlockwise is the north pole.
Face rule: the end from which the current is seen to flow clockwise is the south pole.

The clock rule is examined every year

Looking at one end of the solenoid, anticlockwise current means that end is the north pole and clockwise current means that end is the south pole.Get the two the right way round, since an anticlockwise and south pole answer is the single most common error in this chapter.The field of a solenoid becomes stronger with more turns and with a larger current, so both the number of turns and the current are quoted in questions that ask for a comparison.

Force on a Conductor and Fleming's Left Hand Rule

A current-carrying conductor placed in a magnetic field experiences a force, and the conductor moves unless the field, the current or the conductor itself is arranged so that no net force acts. The strength of the force increases with the current, with the strength of the magnetic field and with the length of the conductor lying in the field.The direction of this force is fixed by Fleming's left hand rule. Stretch the fingers of the left hand so that the thumb, the forefinger and the middle finger are mutually perpendicular, and the rule names what each of the three corresponds to.

A current-carrying conductor in a magnetic field experiences a force, and it is the current that creates the field to act with.
Thumb: stretched along the direction of motion of the conductor, so it gives the direction of the force.
Forefinger: pointed along the direction of the magnetic field, taken from the north pole to the south pole.
Middle finger: pointed along the direction of the current in the conductor.
The three fingers are mutually perpendicular, which is the condition of the rule.
The rule is named the left hand rule, and the right hand is used for the thumb rule of a straight conductor, so do not swap them.

Learn the three-finger order once

The order is thumb for motion, forefinger for field and middle finger for current, and reading it as the sentence T-M-F is not enough, so say the sentence out loud: thumb for force, forefinger for field, middle finger for current.The magnetic field direction is always taken from the north pole towards the south pole, and reversing the forefinger reverses the predicted motion.When the conductor is placed so that the current and the field are in the same direction, there is no force on it at all, which is worth remembering for a one-mark question.

Direct Current and Alternating Current

Direct current flows in one direction only, and it does so through a cell or a battery, where the positive terminal stays positive and the negative terminal stays negative for as long as the cell lasts. The current it drives is steady and does not reverse.Alternating current reverses its direction periodically, and it is the current supplied to homes through the mains. The supply in India reverses fifty times a second, so the frequency of the mains is 50 hertz, which means fifty cycles each of one-fiftieth of a second. A device that works on alternating current is marked with a tilde or a wave symbol.

Direct current flows in one direction only, and it comes from a cell or a battery.
Alternating current reverses its direction periodically, and the supply to homes is alternating current.
The frequency of the alternating mains in India is 50 hertz, and each cycle therefore lasts 0.02 second.
Frequency is the number of oscillations or cycles completed in one second, and it is measured in hertz.
The peak value of alternating current is greater than its effective or rms value, which is why the mains rating of an appliance is quoted as 220 volts.
Both kinds of current produce a magnetic field, since a magnetic field depends on the current and not on its direction of flow being fixed.

The values to memorise

The frequency of the alternating current supplied in India is 50 hertz, and this number appears in almost every examination on this topic.One cycle takes 1 divided by 50, that is 0.02 second, which is the value to use if the time of one cycle is asked.Direct current is marked with a straight line on the rating plate of an appliance and alternating current with a tilde, so the symbols themselves are examinable.

Why Alternating Current Is Used

Alternating current is used for transmission and in the home mainly because its voltage can be changed easily with a transformer, while the voltage of direct current cannot. A transformer works only on alternating current, and it can raise the voltage for transmission and lower it again for use.Sending power at a high voltage greatly reduces the current for the same power, since power equals potential difference multiplied by current, and a smaller current means less heat is produced in the transmission wires. Less heat means less energy wasted, so the step-up and step-down of voltage is the whole reason the supply to homes is alternating current.

The voltage of alternating current can be increased or decreased easily with a transformer, and direct current cannot.
A transformer steps the voltage up for transmission from the generating station to the main lines.
A transformer steps the voltage down again before the power reaches the consumer.
For the same power, P equals VI shows that a higher voltage means a lower current in the transmission wires.
Less current means less heat, since the heat produced is I squared multiplied by R, so much less energy is lost in transmission.
Alternating current is therefore cheaper to transmit over long distances than direct current.

Chain the two ideas in the answer

A good answer runs as one chain: alternating current can be transformed, a higher voltage is used for transmission, a higher voltage means a smaller current for the same power, and a smaller current means less heat and less loss in the wires.Linking the two formulas P equals VI and H equals I squared Rt is what separates a full-mark answer from a list of disconnected points.A transformer cannot be used on direct current, so if a question asks why a step-down transformer cannot reduce a battery's voltage, that is the reason to give.

Domestic Electric Circuits and Safety

Electricity is brought into a house through three wires carried on a three-pin plug, the live wire, the neutral wire and the earth wire. The live wire is at a high potential difference above the earth, the neutral wire completes the circuit at almost zero potential difference, and the earth wire is connected to a metal plate buried in the ground.A high-tension line is dangerous because the potential difference between it and the earth is very large, and a person touching both at the same time completes a circuit through their own body. Domestic safety therefore depends on the fuse in the live wire and on the earth wire, and both are asked by name.

The live wire carries the current to the appliance and is the wire in which a fuse is fitted.
The neutral wire completes the circuit and is at almost zero potential difference above the earth.
The earth wire is connected to a metal plate in the ground and does not carry current in normal working.
Overloading occurs when too many appliances are run on one circuit, and the fuse melts to break it.
Short circuit occurs when the live and neutral wires touch directly, and the fuse wire melts at once.
A high-tension line is dangerous because its potential difference above the earth is very large, and the earth wire is what protects a person in the house.

Where the earth wire earns its mark

In a leakage of current, the current finds a low-resistance path through the earth wire instead of through the body, so the fuse wire melts and the supply is cut off.Without an earth wire the current would pass through the person, and the earth wire is therefore described as a safety device rather than as a working wire.The fuse wire itself is made of an alloy of high resistivity and low melting point such as nichrome, so it melts before the mains wiring does.

Quick Revision

Key formulas at a glance

Memorise these equations — direct application numericals and derivations in CBSE & JEE frequently hinge on these.

Field of a straight conductor

B \propto \frac{1}{r}

The magnetic field around a straight wire weakens as the distance r from the wire increases.

Field of a solenoid

B_{so l} \propto n I

The field inside is proportional to the number of turns n and to the current I, and it is nearly uniform.

Fleming's left hand rule

thumb \to F, forefinger \to B, middle \to I

F is the force or motion, B the field from north to south, and I the current in the conductor.

Frequency of a.c.

f = \frac{1}{T}, f_{I n d ia} = 50 Hz, T = 0.02 s

The mains in India reverses fifty times a second, so one full cycle lasts two hundredths of a second.

Direct and alternating current

D.C. \to one direction only, A.C. \to reverses f times per second

A cell gives direct current, and the supply to homes is alternating current.

Why a.c. is stepped up

P = V I, H = I^{2} R

A higher voltage means a lower current for the same power, and a lower current means less heat in the transmission wires.

Exam Strategy

How this chapter is asked

High-yield question patterns observed across CBSE boards, JEE Main & Advanced, and NEET.

A magnetic field is defined as the region in which a magnetic compass needle shows a deflection, not as the region in which a magnet can be placed.
Magnetic field lines never cross and are closer together where the field is strong, and that spacing is what shows the strength of the field.
Around a straight current-carrying conductor the field lines are concentric circles perpendicular to the wire, and their direction comes from the right-hand thumb rule.
A solenoid behaves like a bar magnet, and anticlockwise current at an end makes that end the north pole while clockwise current makes it the south pole.
The field inside a solenoid is uniform and along the axis, and it becomes stronger with more turns and with a larger current.
Fleming's left hand rule: thumb along the motion, forefinger along the field from north to south, and middle finger along the current, with the three mutually perpendicular.
The frequency of the alternating mains in India is 50 hertz and one cycle takes 0.02 second, while direct current flows one way only from a cell.
The advantage of alternating current is that a transformer can change its voltage, so it can be stepped up for transmission and stepped down for use with less loss of energy.
Domestic safety rests on three named parts: the live wire with its fuse, the neutral wire that completes the circuit, and the earth wire that protects the person, with overloading and short circuit as the two faults.

FAQ

Frequently asked questions

How does an electric current produce a magnetic field?

Whenever a current flows through a straight conductor, a magnetic field is set up all around it, and the field lines are concentric circles whose centres lie on the wire. Oersted's observation was the first evidence of this, since a compass needle placed near the wire deflects as soon as the current is switched on. The field is strongest at the surface of the wire and becomes weaker as the distance from the wire increases. The direction of the field is given by the right-hand thumb rule, and reversing the current reverses every field line.

How is a solenoid made to behave like a bar magnet?

A solenoid is a coil of insulated wire wound closely in many turns over a cylindrical core, and the fields of the individual turns add together to give a strong field along the axis. Outside the coil that field has exactly the pattern of a bar magnet, with a north pole at one end and a south pole at the other, and the field inside is nearly uniform. The two ends are identified by looking at the face of the coil, where anticlockwise current marks the north pole and clockwise current marks the south pole. The field becomes stronger if the number of turns or the current is increased.

State Fleming's left hand rule and explain what each finger gives.

Fleming's left hand rule gives the direction of the force on a current-carrying conductor placed in a magnetic field. The hand is stretched so that the thumb, the forefinger and the middle finger are mutually perpendicular. The thumb is pointed along the direction in which the conductor moves and therefore gives the direction of the force. The forefinger is pointed along the magnetic field from the north pole to the south pole, and the middle finger is pointed along the direction of the current in the conductor.

What is the difference between direct current and alternating current?

Direct current flows in one direction only, and it is obtained from a cell or a battery, so the current through a circuit is steady. Alternating current reverses its direction periodically, and the supply to homes is of this kind. The frequency of the alternating mains in India is 50 hertz, which means fifty complete cycles every second, so one cycle lasts 0.02 second. Appliances are marked with a straight line for direct current and with a tilde for alternating current. Both kinds produce a magnetic field, because a magnetic field depends on a current and not on whether its direction is fixed.

Why is alternating current supplied to homes rather than direct current?

The main reason is that a transformer can change the voltage of an alternating current easily, and a transformer cannot be used on direct current. The voltage can be stepped up at the generating station for transmission and then stepped down again before reaching the consumer. For the same power, since P equals VI, a higher voltage means a lower current in the transmission wires. The heat produced in those wires is I squared multiplied by R, so a lower current means far less energy is wasted, and that is what makes long-distance transmission economical. The whole argument is the reason the supply to homes is alternating current.

How do the three wires and the fuse make a domestic circuit safe?

The live wire carries the current to the appliance at high potential difference above the earth, and the neutral wire carries it back at almost zero potential difference to complete the circuit. The earth wire is connected to a metal plate in the ground and provides a low-resistance path, so in a leakage the current flows through it instead of through a person, the fuse wire melts and the supply is cut off. The two faults that cause this are overloading, when too many appliances are run on one circuit, and a short circuit, when the live and neutral wires touch. A high-tension line is dangerous because its potential difference above the earth is very large.

Next Chapters

Continue learning

Class 10 Science Notes Electricity Class 10 Notes The Human Eye and Colourful World Class 10 Notes Light, Reflection and Refraction Class 10 Notes

Master this chapter with expert live guidance

Self-study notes lay the ground, but conceptual doubts clear fastest in an interactive classroom. Narayan Gurukul Academy (ClassApna) conducts small-batch CBSE, JEE & NEET coaching with daily doubt solving and rigorous mock tests.

Book a Free Demo Class Explore Plans & Batches

Small batches · 1-on-1 personal mentorship · Live online & offline centre