Magnetism & Electromagnetism

Why This Chapter Matters

Expect 2 to 3 questions from magnetism in almost every SSC and RRB physics paper, and it shows up more often than sound or gravitation because examiners love the electric motor, generator, and compass questions here. These are pure fact-recall questions: what a magnet does, what an electromagnet is, who found what, and how a compass points north. Nobody is asking you to derive a formula.

The single biggest mistake aspirants make is mixing up the motor and the generator. Both machines use the same basic parts, a coil and a magnetic field, but they do opposite jobs. A motor eats electricity and gives you motion. A generator eats motion and gives you electricity. Students who blur this line lose an easy mark every single time it appears, and it appears often. Keep that one line in your head through this whole chapter and you will never fall for the trap again.

1. What Is a Magnet, and Why Does It Behave the Way It Does

A magnet is any object that attracts iron, cobalt, and nickel, and that always settles pointing roughly north-south when left free to rotate. That second property is not a side detail, it is the whole reason the compass exists, and we will come back to it.

Every magnet, no matter how small you cut it, has two poles: a north pole and a south pole. Cut a bar magnet into two pieces and you do not get an isolated north pole and an isolated south pole. You get two smaller magnets, each with its own north and south pole. This is a favourite SSC one-liner: a magnetic monopole does not exist in nature.

Exam trap: like poles repel, unlike poles attract. Students under exam pressure sometimes flip this, especially when the question is phrased with a double negative. Read it twice before answering.

Memory hook: think of two people from the same hometown meeting a stranger's town. "Same-same" pushes apart in a crowd (repel), "opposite" pulls together out of curiosity (attract). Same poles repel, opposite poles attract.

Types of magnets

Type	Example	Key fact
Natural magnet	Magnetite (lodestone)	Naturally magnetic iron ore, the first magnet humans ever used
Artificial permanent magnet	Bar magnet, horseshoe magnet	Made by rubbing/induction, keeps its magnetism without external power
Temporary magnet	Soft iron piece near a magnet	Loses magnetism almost instantly once the external magnet is removed
Electromagnet	Coil of wire around a soft iron core, current flowing	Magnetic only while current flows, strength is adjustable

Soft iron makes a good temporary magnet and a good electromagnet core because it magnetises easily and demagnetises easily. Steel is the opposite: hard to magnetise, but once magnetised it holds on stubbornly. That is exactly why steel, not soft iron, is used to make permanent magnets and compass needles.

2. Magnetic Field — the Invisible Zone of Influence

A magnetic field is the region around a magnet where its force can be felt by another magnetic material. You cannot see it, but you can map it with magnetic field lines, which run from the north pole to the south pole outside the magnet, and from south to north inside it, forming closed loops. Field lines never cross each other, and they are denser where the field is stronger, typically right at the poles.

Analogy: picture a crowded railway platform announcement. The announcer's voice (the field) is loudest right next to the speaker (the pole) and fades as you walk away. You cannot see sound waves either, but you know the zone where the voice reaches by how clearly you hear it. Magnetic field lines work the same way, dense near the poles, thinning out with distance.

The SI unit of magnetic field strength (magnetic flux density) is the tesla (T), named after Nikola Tesla. A smaller, older unit still seen in some questions is the gauss.

3. Electromagnetism — Where Electricity and Magnetism Meet

For centuries, electricity and magnetism were treated as two separate topics. That changed in 1820, when Danish physicist Hans Christian Oersted noticed something almost by accident during a lecture: a compass needle placed near a current-carrying wire deflected. This single observation proved that a moving electric current creates a magnetic field around itself. It is the founding fact of electromagnetism and a very commonly asked discoverer-pair question.

Exam trap: Oersted discovered that current produces magnetism. It was Michael Faraday, in 1831, who discovered the reverse effect, that a changing magnetic field produces (induces) current. These are two different scientists and two different directions of the same relationship. SSC papers love testing this pair against each other.

Right-hand rules (fact-level, no derivation needed)

You just need to know these rules exist and roughly what they tell you, not derive them.

• Maxwell's right-hand thumb rule (or the grip rule): if you hold a current-carrying straight wire in your right hand with the thumb pointing in the direction of current flow, your curled fingers show the direction of the magnetic field circling the wire.
• Fleming's left-hand rule: used for motors. It tells you the direction of force (motion) on a current-carrying conductor placed in a magnetic field.
• Fleming's right-hand rule: used for generators. It tells you the direction of the induced current when a conductor moves inside a magnetic field.

Memory hook: Left hand for the machine that Leaps into motion (motor), Right hand for the machine that Releases current (generator, generates). Left-Leaps-motor, Right-Releases-current.

Electromagnet

Wind an insulated copper wire into a coil (called a solenoid) around a soft iron core, and pass current through it. The result is an electromagnet, a magnet that can be switched on and off simply by switching the current on and off. Its strength depends on three things:

1. Number of turns in the coil, more turns means a stronger field.
2. Strength of the current, more current means a stronger field.
3. Material of the core, soft iron gives the strongest field because it magnetises so easily.

Electromagnets are everywhere once you start noticing them: electric bells, electric motors, generators, MRI machines, cranes that lift scrap iron, loudspeakers, and relays. This device-list is a favourite fill-in-the-blank source.

Exam trap: an electromagnet's field can be reversed simply by reversing the direction of current. A permanent magnet's poles are fixed once made. If a question describes a magnet whose polarity you can flip on demand, it is describing an electromagnet.

4. The Electric Motor — Electricity In, Motion Out

An electric motor converts electrical energy into mechanical energy. Inside, a rectangular coil of wire sits between the poles of a permanent magnet. When current flows through the coil, the magnetic field of the magnet pushes on the current-carrying coil (this is the force Fleming's left-hand rule predicts), and the coil spins. A component called the split-ring commutator reverses the current direction every half rotation, which keeps the coil spinning continuously in one direction instead of jerking back and forth.

You meet electric motors constantly: ceiling fans, washing machines, mixers, electric cars, and water pumps all run on this exact principle.

5. The Electric Generator (Dynamo) — Motion In, Electricity Out

A generator does the reverse job: it converts mechanical energy into electrical energy. This works on Faraday's law of electromagnetic induction, which states that moving a conductor through a magnetic field, or changing the magnetic field around a conductor, induces (creates) an electric current in that conductor.

Inside a simple generator, a coil is mechanically rotated between the poles of a magnet (or the magnet is rotated around a fixed coil). As the coil turns, it induces a current, and the direction is predicted by Fleming's right-hand rule. Turn the coil faster, and you get more induced current.

Analogy: think of a hand-crank flashlight or the dynamo-powered bicycle light you may have used. Pedal harder, the coil inside spins faster past the magnet, and the bulb glows brighter. That is a generator working in miniature, right on your bicycle wheel.

Power stations use this exact idea at massive scale. A thermal, hydro, or nuclear power plant does not create electricity from nothing, it spins a giant turbine (using steam, falling water, or another force) connected to a generator, and the generator's rotating coil induces current. Every major power plant in the world, no matter its fuel source, ultimately relies on Faraday's principle of electromagnetic induction to actually produce electricity.

Motor vs generator, side by side

Feature	Electric motor	Electric generator
Converts	Electrical energy to mechanical energy	Mechanical energy to electrical energy
Input	Electric current	Rotational/mechanical motion
Output	Motion (rotation)	Electric current
Governing rule	Fleming's left-hand rule	Fleming's right-hand rule / Faraday's law
Everyday example	Fan, mixer, washing machine	Power plant dynamo, bicycle dynamo light

6. Earth's Magnetism and the Compass

Earth itself behaves like a giant, weak bar magnet, with a magnetic field surrounding the planet. This is why a freely suspended magnetic needle, like the one in a compass, always aligns itself roughly north-south. The needle's north pole is attracted toward Earth's magnetic pole located near the geographic North, and its south pole toward the magnetic pole near the geographic South.

Here is the detail that trips up almost everyone: Earth's magnetic pole near the geographic North Pole actually behaves as a magnetic south pole (because it attracts the north-seeking pole of a compass needle, and unlike poles attract). Most SSC-level questions do not test this reversal directly, so do not lose sleep over it, but do not be shocked if you see the phrase "geomagnetic south pole is near the geographic North Pole" in a distractor option; it is factually correct, not a typo.

Earth's magnetic axis does not line up exactly with its rotation (geographic) axis, they are tilted from each other by roughly 11 degrees. This is why a compass needle points to magnetic north, not exactly true (geographic) north, an angle of difference called the magnetic declination.

Exam trap: magnetic north and geographic (true) north are NOT the same point on Earth. A compass gives you magnetic north. This distinction is a repeat offender in SSC option sets.

Why does Earth have a magnetic field at all? The mainstream explanation taught at this level is the dynamo effect: molten, electrically conducting iron and nickel churn in Earth's outer core, and this moving conducting fluid generates the planet's magnetic field, much like a spinning coil generates current in a generator.

Earth's magnetic field also does something protective: it deflects most of the charged particles streaming from the Sun (the solar wind), shielding the atmosphere and life on the surface. When some of these particles do slip in near the poles, they collide with gas particles in the upper atmosphere and glow, producing the aurora (aurora borealis in the north, aurora australis in the south).

How a compass actually works, step by step

1. The compass needle is itself a small permanent magnet, free to rotate on a pivot.
2. Earth's magnetic field exerts force on the needle's poles.
3. The needle rotates until it aligns with the local magnetic field, pointing its north-seeking end toward magnetic north.
4. Since the field is present everywhere on Earth's surface, the compass works anywhere outdoors, no batteries, no signal, which is exactly why it remains standard survival and navigation equipment even in the GPS era.

7. Magnetic Materials — Ferromagnetic, Paramagnetic, Diamagnetic

Not every material responds to a magnet the same way. SSC occasionally asks a direct classification question here.

Category	Behaviour	Examples
Ferromagnetic	Strongly attracted, can be magnetised themselves	Iron, cobalt, nickel
Paramagnetic	Weakly attracted	Aluminium, platinum
Diamagnetic	Weakly repelled	Copper, bismuth, water

Memory hook: "Fero" sounds like "fierce", ferromagnetic materials react fiercely (strongly) to a magnet. That single sound-alike keeps the strongest category straight under pressure.

A ferromagnetic material loses its magnetic properties above a certain temperature, called the Curie temperature (or Curie point), because the heat disrupts the internal alignment that makes it magnetic. For iron, this happens at roughly 770 degrees Celsius. You do not need the exact number for most exams, just the concept: heat a magnet enough, and it stops being a magnet.

8. Everyday Devices Built on Magnetism

Grounding these facts in devices you have actually touched makes them stick far better than memorising definitions in isolation.

• Electric bell: an electromagnet pulls a metal hammer to strike a gong; the same motion breaks the circuit momentarily, the electromagnet switches off, a spring pulls the hammer back, the circuit closes again, and the cycle repeats rapidly, producing the ringing sound.
• Loudspeaker: converts electrical audio signals into sound using a coil placed in a magnetic field; the varying current makes the coil (and attached cone) vibrate, pushing air to create sound waves.
• MRI machine (Magnetic Resonance Imaging): uses a very powerful electromagnet along with radio waves to produce detailed images of the inside of the body, without surgery or radiation exposure (unlike an X-ray).
• Maglev train: uses powerful electromagnets to make the train levitate above the track and to propel it forward, eliminating wheel friction almost entirely, which allows very high speeds.
• Electromagnetic crane: the giant crane you see lifting scrap cars and iron sheets at a scrapyard is simply a huge electromagnet; switch off the current and it drops the load instantly, which is exactly why the operator has to be so careful about positioning before switching off.
• Transformer: works on Faraday's principle of electromagnetic induction, and is used to step voltage up or down, essential for transmitting electricity efficiently over long power lines.

9. A Short Timeline Worth Locking In

Year	Event	Person
Ancient period	Natural magnetism observed in lodestone	Known to ancient Greeks and Chinese, no single discoverer
1820	Current-carrying wire deflects a compass needle (current creates magnetism)	Hans Christian Oersted
1820s	Force on a current-carrying wire in a magnetic field, and related electrodynamics laws	Andre-Marie Ampere
1831	Electromagnetic induction (changing magnetic field creates current)	Michael Faraday

Exam trap: Ampere's name is attached to the SI unit of electric current, the ampere, and to laws describing the magnetic effect of current. Do not confuse Ampere's contribution (relating current and magnetic force) with Oersted's (the first discovery that current produces a field at all) or Faraday's (induction, the reverse effect).

10. Lenz's Law and Why Direction Matters

There is one more name worth knowing alongside Faraday: Heinrich Lenz. In 1834 he stated what is now called Lenz's law, which says the direction of an induced current always opposes the very change that produced it. If you push a magnet into a coil, the induced current creates its own magnetic field that pushes back against the incoming magnet, resisting the motion. This is not the universe being difficult for no reason, it is a direct consequence of the law of conservation of energy. If the induced current helped the motion instead of opposing it, you would get energy for free out of nothing, which never happens in a closed system.

You do not need the mathematics behind Lenz's law for SSC-level papers. You need the one-line idea: induced effects always oppose their cause. This single sentence explains why a generator gets physically harder to crank the more current it supplies, something you may have felt firsthand cycling a dynamo-powered bicycle light uphill. The harder the bulb glows, the more resistance you feel in the pedals, because the induced current is fighting your effort exactly as Lenz's law predicts.

11. Magnetic Effect of Current in a Straight Wire, a Loop, and a Solenoid

The shape of a current-carrying conductor changes the shape of the magnetic field it produces, and SSC occasionally tests this at a purely descriptive level.

• Straight wire: the field forms concentric circles around the wire, strongest close to the wire and weakening with distance, exactly as Maxwell's grip rule describes.
• Circular loop: the field lines bunch together and pass through the centre of the loop in one direction, effectively making the loop behave like a flat disc magnet with one face acting as a north pole and the other as a south pole.
• Solenoid: stack many loops together into a coil, and the field inside becomes strong and nearly uniform, running along the axis of the coil just like the field inside a bar magnet. This is precisely why a solenoid wrapped around a soft iron core makes such an effective electromagnet, the coil shape concentrates the field where you actually want it, inside the core.

Analogy: think of a single loop as one person clapping, a small, localised burst of sound. A solenoid is an entire stadium section clapping in rhythm together, the combined effect is far stronger and more focused than any one clap alone, just as the combined field of many loops is far stronger than the field of a single wire.

12. A Note on AC, DC, and Why This Matters for Generators

Power stations generate alternating current (AC), current that reverses direction periodically, rather than direct current (DC), which flows in one direction only (the kind you get from a battery). This is not a random design choice. AC can be stepped up to very high voltage using a transformer, sent over long-distance power lines with much lower energy loss, and then stepped back down to a safe voltage before it reaches your home. DC cannot be transformed this way as easily, which is why national and state electricity grids run almost entirely on AC, and why the transformer sitting on a pole near your house is such a familiar sight.

Exam trap: do not assume "current" in these questions always means DC. When a question describes household supply, power lines, or a generator at a power plant, it is almost certainly asking about AC unless it explicitly says otherwise.

Quick Revision — One-Line Facts

• Every magnet has two poles, north and south; isolated monopoles do not exist.
• Like poles repel, unlike poles attract.
• Magnetic field lines run from north to south outside a magnet, and never cross.
• SI unit of magnetic field strength is the tesla (T).
• Hans Christian Oersted (1820) discovered current-carrying wires produce a magnetic field.
• Michael Faraday (1831) discovered electromagnetic induction, the reverse effect.
• Andre-Marie Ampere gave his name to the SI unit of current and to laws of electrodynamics.
• Electromagnets are made by winding wire (a solenoid) around a soft iron core.
• Electromagnet strength depends on number of turns, current strength, and core material.
• Soft iron is used for electromagnets because it magnetises and demagnetises easily.
• Steel is used for permanent magnets and compass needles because it retains magnetism.
• An electric motor converts electrical energy into mechanical energy.
• An electric generator converts mechanical energy into electrical energy.
• Fleming's left-hand rule applies to motors (force direction).
• Fleming's right-hand rule applies to generators (induced current direction).
• The split-ring commutator keeps a motor's coil spinning in one direction.
• All major power plants ultimately use a generator based on Faraday's induction principle.
• Earth behaves like a giant weak bar magnet.
• The compass needle aligns with Earth's magnetic field, not exactly true geographic north.
• The angle between magnetic north and true north is called magnetic declination.
• Earth's magnetic and geographic axes are tilted by about 11 degrees to each other.
• The likely cause of Earth's magnetic field is the dynamo effect in the molten outer core.
• Earth's magnetic field deflects the solar wind and helps produce the aurora near the poles.
• Ferromagnetic materials (iron, cobalt, nickel) are strongly attracted to magnets.
• Paramagnetic materials (aluminium, platinum) are weakly attracted to magnets.
• Diamagnetic materials (copper, bismuth, water) are weakly repelled by magnets.
• A ferromagnetic material loses magnetism above its Curie temperature.
• MRI machines use powerful electromagnets and radio waves, not X-rays, for imaging.
• Maglev trains use electromagnets to levitate and propel without wheel friction.
• A transformer changes voltage level using the principle of electromagnetic induction.
• An electromagnetic crane can drop its load instantly by switching off the current.

Memory Tables

Table 1 — Discoverer and Rule Reference

Concept	Associated name(s)	One key fact
Current creates magnetism	Hans Christian Oersted (1820)	Compass needle deflected near current-carrying wire
Electromagnetic induction	Michael Faraday (1831)	Changing magnetic field induces current
Unit of current, electrodynamics laws	Andre-Marie Ampere	SI unit "ampere" named after him
Force direction in a motor	Fleming's left-hand rule	Applies where current meets an external field
Induced current direction in a generator	Fleming's right-hand rule	Applies when a conductor moves through a field
Unit of magnetic field strength	Nikola Tesla	SI unit is the tesla (T)

Table 2 — Motor vs Generator vs Electromagnet

Device	Energy conversion	Key rule/principle	Common example
Electric motor	Electrical to mechanical	Fleming's left-hand rule	Ceiling fan, mixer
Electric generator	Mechanical to electrical	Faraday's induction / Fleming's right-hand rule	Power plant dynamo
Electromagnet	Electrical current to magnetic field	Current around soft iron core	Electric bell, crane
Transformer	Voltage change (AC)	Electromagnetic induction	Power transmission lines

Table 3 — Magnetic Material Behaviour

Category	Response to magnet	Common examples
Ferromagnetic	Strongly attracted	Iron, cobalt, nickel
Paramagnetic	Weakly attracted	Aluminium, platinum
Diamagnetic	Weakly repelled	Copper, bismuth, water

Practice MCQs

Q1. Which of the following statements about magnetic poles is correct? (a) A magnet can have only one pole if cut carefully (b) Isolated magnetic monopoles do not exist in nature (c) Like poles always attract each other (d) Unlike poles always repel each other

Q2. What is the SI unit of magnetic field strength (magnetic flux density)? (a) Newton (b) Weber (c) Tesla (d) Ampere

Q3. Which material is preferred for making the core of an electromagnet? (a) Steel (b) Soft iron (c) Copper (d) Aluminium

Q4. Who discovered that a current-carrying conductor produces a magnetic field around it? (a) Michael Faraday (b) James Clerk Maxwell (c) Hans Christian Oersted (d) Andre-Marie Ampere

Q5. An electric motor converts: (a) Mechanical energy into electrical energy (b) Electrical energy into mechanical energy (c) Chemical energy into electrical energy (d) Heat energy into mechanical energy

Q6. A compass needle placed anywhere on Earth's surface aligns itself roughly along: (a) The equator (b) Earth's rotational axis exactly (c) Earth's magnetic north-south direction (d) The nearest electric power line

Q7. Which of the following materials is diamagnetic, meaning it is weakly repelled by a magnet? (a) Iron (b) Aluminium (c) Copper (d) Cobalt

Q8. The component in a simple electric motor that reverses current direction every half rotation, keeping the coil spinning in one direction, is called the: (a) Solenoid (b) Split-ring commutator (c) Armature magnet (d) Field regulator

Q9. Michael Faraday's discovery of electromagnetic induction in 1831 established that: (a) A stationary magnet can generate unlimited current (b) A changing magnetic field can induce an electric current in a conductor (c) Current always flows from south to north pole (d) Electromagnets are weaker than permanent magnets

Q10. Which rule is used to find the direction of induced current in an electric generator? (a) Fleming's left-hand rule (b) Fleming's right-hand rule (c) Maxwell's grip rule only (d) Lenz's first rule

Q11. The angle between magnetic north (shown by a compass) and true geographic north at a given place is known as: (a) Magnetic dip (b) Magnetic declination (c) Magnetic saturation (d) Magnetic latitude

Q12. MRI (Magnetic Resonance Imaging) machines primarily use: (a) X-rays and a weak magnet (b) Radioactive isotopes (c) A powerful electromagnet and radio waves (d) Ultrasonic sound waves only

Q13. The most widely accepted explanation for the origin of Earth's magnetic field is: (a) Static electricity in the atmosphere (b) The dynamo effect caused by molten conducting material moving in the outer core (c) Solar radiation striking the equator (d) Magnetic rocks on the surface of the crust

Q14. A ferromagnetic material loses its magnetic properties when heated above its: (a) Melting point (b) Boiling point (c) Curie temperature (d) Triple point

Q15. Which of these best distinguishes a permanent magnet from an electromagnet? (a) A permanent magnet's field cannot be switched off or reversed on demand, while an electromagnet's can (b) A permanent magnet is always stronger than an electromagnet (c) An electromagnet has only one pole (d) A permanent magnet requires a continuous current supply

Answer Key

Q	Answer	Reason
Q1	(b)	Cutting a magnet always produces two new magnets, each with its own pair of poles; monopoles do not exist.
Q2	(c)	The tesla, named after Nikola Tesla, is the SI unit of magnetic flux density.
Q3	(b)	Soft iron magnetises and demagnetises quickly, ideal for a switchable electromagnet core.
Q4	(c)	Oersted's 1820 observation of a deflecting compass needle founded the field of electromagnetism.
Q5	(b)	A motor takes in electrical energy and outputs mechanical motion, the opposite of a generator.
Q6	(c)	Earth behaves like a giant bar magnet, so a free compass needle aligns with its magnetic field.
Q7	(c)	Copper is weakly repelled by a magnet, making it diamagnetic, unlike iron and cobalt which are ferromagnetic.
Q8	(b)	The split-ring commutator flips current direction each half turn, keeping rotation continuous in one direction.
Q9	(b)	This is the core statement of electromagnetic induction, the working principle behind every generator.
Q10	(b)	Fleming's right-hand rule gives induced current direction in a generator; the left-hand rule is for motors.
Q11	(b)	Magnetic declination is the angular difference between magnetic north and true (geographic) north at a location.
Q12	(c)	MRI uses a strong electromagnet with radio waves for imaging, avoiding the radiation exposure of an X-ray.
Q13	(b)	The dynamo effect, from moving molten conducting material in the outer core, is the mainstream explanation taught for Earth's field.
Q14	(c)	Above the Curie temperature, thermal energy disrupts the internal alignment that gives a material its magnetism.
Q15	(a)	Only an electromagnet's field can be switched on, off, or reversed simply by controlling the current through it.