Magnetic Effects of Electric Current — Class 10 Science
What CBSE examines here (2026-27). This is the biggest single removal found across all of Class 10 Science: the current chapter has no dedicated sections on the electric motor, electromagnetic induction, or the electric generator at all. It covers magnetic field lines, the field around a straight wire/loop/solenoid, electromagnets, the force on a current-carrying conductor (Fleming's left-hand rule, direction only — there is no F = BIL formula and the unit "tesla" is never named), and domestic circuits (AC 220 V/50 Hz supply, live/neutral/earth wires, fuses). Motors and generators are named in one single sentence as examples of devices that use magnetic force — nothing more. One exercise question (Q7(iii), asking for the rule governing "current induced in a coil due to its rotation in a magnetic field") does survive from the older syllabus even though induction is never explained in the current text — it's answered here using Fleming's right-hand rule, flagged as drawing on content this chapter no longer teaches.
1. About the Chapter
This chapter, in its current (2026-27) form, covers:
- Magnetic field of currents (straight wire, loop, solenoid, electromagnet)
- Force on conductor in magnetic field (direction only, via Fleming's left-hand rule)
- Domestic electrical circuits
Electric motors, electromagnetic induction and electric generators — all covered in detail below — are kept for reference but are not part of the current syllabus; see the callout above and the appendix.
Why Important
- Electric motors EVERYWHERE (fans, mixers, cars, trains)
- Power generation (all electricity made by generators)
- Modern technology depends on this
2. Magnetic Field
Definition
Region around a magnet where its magnetic force is experienced.
Field Lines
Imaginary lines showing direction of magnetic field.
Properties:
- Always go from NORTH to SOUTH outside magnet
- Closed loops (form complete circuits)
- Never intersect
- Closer lines = stronger field
(This chapter doesn't introduce a unit for magnetic field strength or a quantitative formula for it — tesla, the standard SI unit, isn't named here.)
3. Oersted's Discovery (1820)
Experiment
Hans Christian Oersted noticed that a magnetic compass needle near a CURRENT-CARRYING WIRE got DEFLECTED.
Conclusion
Electric current produces magnetic field around it.
This was the BEGINNING of electromagnetism — one of physics' greatest discoveries.
4. Magnetic Field around Current-Carrying Conductors
Straight Wire
Right-Hand Thumb Rule:
- Hold wire with right hand
- THUMB points in direction of CURRENT
- CURLED FINGERS show direction of MAGNETIC FIELD
Field lines are CONCENTRIC CIRCLES around wire.
Circular Loop
When current flows in a circular loop:
- Magnetic field at centre is PERPENDICULAR to plane of loop
- Field is stronger if more current or more turns
Solenoid
A coil of insulated wire wrapped tightly.
When current flows:
- Strong magnetic field INSIDE — uniform and parallel
- Like a BAR MAGNET — has North and South poles
- Direction determined by RIGHT-HAND THUMB RULE
Electromagnet
A SOLENOID with a SOFT IRON CORE inside.
- When current ON: behaves as STRONG MAGNET
- When current OFF: magnetism DISAPPEARS
Uses:
- Electric bells, doorbells
- Lifting magnets in junkyards
- MRI machines
- Speakers
5. Force on Current-Carrying Conductor
When a current-carrying conductor is placed in a magnetic field, it EXPERIENCES a FORCE — largest when the current is at right angles to the field. This chapter gives no formula for the magnitude of this force, only its direction.
Direction — Fleming's Left-Hand Rule
Stretch left hand: thumb, forefinger (first finger), middle finger MUTUALLY PERPENDICULAR.
- First finger: direction of MAGNETIC FIELD
- Second (middle) finger: direction of CURRENT
- THUMB: direction of the FORCE (motion)
Devices using this effect — electric motors, generators, loudspeakers, microphones, measuring instruments — are named in this chapter as examples, but only the electric motor and generator are given dedicated sections below, both of which are beyond the current syllabus (see the callout and appendix).
6. Domestic Electrical Circuits
Indian Home Wiring (this chapter's own description)
Homes receive AC power at 220 V, 50 Hz. Three wires:
- LIVE (red insulation): the supply, 220 V relative to neutral
- NEUTRAL (black insulation): the return path
- EARTH (green insulation): connected to a metal plate deep in the ground, for safety
Why Earth Wire?
Metallic-bodied appliances (iron, toaster, fan, fridge) have their body connected to the earth wire. If current leaks to the body, the earth wire gives it a low-resistance path away, keeping the body's potential close to earth's and reducing shock risk.
Parallel Connection
All home appliances are connected in PARALLEL across the live and neutral wires → each gets the same full voltage, with its own separate switch.
Fuse
A piece of wire (of a specific melting point) placed in series with the circuit. If current exceeds the rated value, Joule heating melts the fuse wire, breaking the circuit before damage occurs. Domestic fuses are commonly rated 1 A, 2 A, 3 A, 5 A, 10 A, etc. (This chapter names only the fuse, not the MCB, as its safety device.)
Short Circuit / Overloading
A short circuit happens when the live and neutral wires touch directly (e.g. damaged insulation), causing current to increase abruptly. Overloading can also happen from a voltage surge or from too many appliances on one socket. Two separate household circuits are typically used — a 15 A circuit for high-power appliances (geysers, coolers) and a 5 A circuit for lights and fans.
7. Worked Examples
Example 1: Direction
A current flows EASTWARD in a wire. Find direction of magnetic field BELOW wire.
Using right-hand thumb rule:
- Thumb points EAST
- Fingers curl: NORTH (above wire) to SOUTH (below wire)
- BELOW wire: direction is NORTHWARD
Example 2: Direction of force (Fleming's left-hand rule)
A current flows through a conductor placed at right angles to a magnetic field. How do you find the direction of the force on it?
- Point the first finger along the field, the second finger along the current — the thumb then gives the force direction.
- (This chapter gives no formula for the force's magnitude, only this rule for its direction.)
Example 3: AC frequency
What is the frequency of Indian AC supply?
- 50 Hz (cycles per second)
- 220V AC — this is stated in this chapter's own domestic-circuits section
8. Common Mistakes
-
Expecting a motor/generator/induction section in this chapter
- This chapter names them as examples of devices using magnetic force, but doesn't teach their construction or working — see the appendix.
-
Reaching for Fleming's right-hand rule in this chapter
- Only the LEFT-hand rule (force on a conductor) is taught here. The right-hand rule (for induced current) belongs to electromagnetic induction, which isn't covered — except that one orphaned exercise question (Q7(iii)) still asks for it.
-
Magnetic field around straight wire
- CIRCULAR (concentric circles), not straight.
-
Expecting a force formula
- This chapter gives no F = BIL formula — only the direction rule (Fleming's left hand) and the qualitative statement that force is largest when current and field are perpendicular.
-
Earth wire purpose
- SAFETY only. Doesn't carry current normally.
9. Indian Context
Indian Heritage
- Jagadish Chandra Bose: early experiments with EM waves
- C.V. Raman: Nobel for scattering of light
Modern Indian
- Indian Railways: increasing electric trains (>95% electrified)
- Tata Power, NTPC, Adani: major power producers
- Bhadla Solar Park (Rajasthan): world's largest single solar park (~2,245 MW)
Indian Goals
- 500 GW renewable by 2030
- Net-zero emissions by 2070
- Electric vehicles push (Tata, Mahindra, Ola)
10. Conclusion
This chapter, as currently examined:
- Oersted's discovery: current produces a magnetic field
- Magnetic fields from a straight wire, loop and solenoid; electromagnets
- Force on a conductor: direction only, via Fleming's left-hand rule
- Home wiring: AC 220V/50Hz supply, live/neutral/earth, fuses
Master:
- Right-hand thumb rule (for field direction)
- Fleming's left-hand rule (force direction only)
- Domestic circuit safety
Electric motors, electromagnetic induction, and generators are real and important physics (see appendix) but are not part of this chapter's current syllabus.
Practice 15+ problems. This is a HIGH-MARK chapter (~10-12 marks).
Electromagnetism: the partnership of electricity and magnetism powering all of modern technology.
Appendix — beyond the current syllabus
Not examinable in CBSE 2026-27. The electric motor, electromagnetic induction, and the electric generator — along with the AC-vs-DC theoretical comparison — have been removed from this chapter entirely. They are kept here because they are genuinely important physics, widely taught elsewhere (Class 12, competitive exams), and because the chapter's own Exercise still contains one question (Q7(iii)) that assumes familiarity with induced current.
Electric Motor
Converts electrical energy to mechanical energy (rotation). A current-carrying coil (armature) sits in a magnetic field between permanent magnets. By Fleming's left-hand rule, the two sides of the coil experience forces in opposite directions, creating a turning effect. A split-ring commutator reverses the current direction every half rotation, so the turning force keeps acting the same way and the coil spins continuously. Brushes maintain electrical contact with the rotating commutator. Used in fans, pumps, mixers, and (in larger form) electric vehicles and trains.
Electromagnetic Induction
Michael Faraday discovered that a changing magnetic field induces a current in a coil — either by moving a magnet near the coil, or by changing the current in a nearby coil. The direction of this induced current is given by Fleming's right-hand rule: first finger along the field, second finger along the direction of motion, thumb gives the direction of the induced current (contrast with the left-hand rule, used for the force on a current-carrying conductor).
Electric Generator
Converts mechanical energy to electrical energy — the reverse of a motor. A coil is mechanically rotated (by water, steam or wind turning a turbine) inside a magnetic field, inducing a current via electromagnetic induction. An AC generator uses slip rings (current reverses direction every half rotation, giving alternating current); a DC generator uses a split-ring commutator instead (current direction stays the same, giving direct current).
AC vs DC
Direct current (DC) flows in one direction with constant magnitude — batteries and cells. Alternating current (AC) periodically reverses direction — Indian household supply is 220 V AC at 50 Hz. AC is preferred for long-distance transmission because transformers can step its voltage up or down efficiently, reducing transmission losses; DC is used where a steady one-directional supply is needed, as in battery-powered devices.
