Bihar Board Class 10 · Science · Matric exam 2027
Chapter 13: Magnetic Effects of Electric Current — notes
The chapter’s 9 parts in the book’s order — the first idea of each and the points Medha Ma’am writes on the board — and the summary at the end. The full lesson and a check question for each part are in the app.
1. Electric current produces a magnetic field
Okay, so, you already know electricity and magnetism are linked, somehow.
- • Current-carrying wire behaves like a magnet
- • Compass needle deflects when current flows nearby
- • Discovered by Oersted in 1820
- • Compass needle = small bar magnet (north pole, south pole)
- • Like poles repel, unlike poles attract
2. Magnetic field and field lines
Okay, so let's talk about magnetic fields.
- • Magnetic field: region around a magnet where its force can be felt
- • Field lines come from iron filings pattern / compass needle motion
- • Field lines: emerge from N pole, merge at S pole (outside)
- • Inside magnet: S pole to N pole
- • Crowded lines = stronger field
- • No two field lines ever cross
3. Magnetic field due to a straight current-carrying conductor and the Right-Hand Thumb Rule
Okay, so — think of a straight wire with current flowing through it, placed over a compass needle.
- • Current in straight wire → magnetic field as concentric circles
- • Reversing current reverses field direction
- • More current → stronger field (more deflection)
- • Farther from wire → weaker field (less deflection)
- • Right-Hand Thumb Rule: thumb = current direction, curled fingers = field direction
4. Magnetic field due to a circular loop and a solenoid
Okay, so let's bend a straight wire into a circular loop.
- • Circular loop: field lines at centre look like straight lines
- • Coil of n turns → field is n × as large as one turn
- • Solenoid = coil of many turns wound like a cylinder
- • Solenoid's field pattern ~ bar magnet (one end N, one end S)
- • Field inside solenoid is uniform (parallel straight lines)
- • Soft iron + solenoid field = electromagnet
5. Force on a current-carrying conductor and Fleming's Left-Hand Rule
Okay, so we know a current makes a magnetic field.
- • Current-carrying conductor in magnetic field feels a force
- • Reversing current reverses direction of force
- • Force is largest when current ⟂ magnetic field
- • Fleming's Left-Hand Rule: forefinger = field, middle finger = current, thumb = force/motion
6. Electric motor and the split ring commutator
Okay, so let's talk about the electric motor.
- • Electric motor: electrical energy → mechanical energy
- • Coil ABCD between magnet poles, split ring = commutator
- • Current flows A→B and C→D (opposite directions)
- • Fleming's Left-Hand Rule: AB pushed down, CD pushed up → rotation
- • Split ring reverses current every half turn → continuous rotation
- • Soft iron core + coil = armature (commercial motors)
7. Electromagnetic induction and Fleming's Right-Hand Rule
Okay, so — Faraday found something lovely.
- • Moving magnet near coil → induced current (galvanometer deflects)
- • Magnet/coil stationary → no deflection
- • Changing current in primary coil → induced current in secondary coil
- • This is electromagnetic induction (Faraday, 1831)
- • Fleming's Right-Hand Rule: forefinger = field, thumb = motion, middle finger = induced current
8. Electric generator: AC and DC
Okay, so let's talk about the electric generator.
- • Generator: mechanical energy → electrical energy
- • Coil ABCD rotates between magnet poles, rings + brushes
- • Fleming's Right-Hand Rule gives current direction
- • Current reverses every half rotation → Alternating Current (AC)
- • Split-ring commutator instead of rings → Direct Current (DC)
- • India: AC frequency = 50 Hz
9. Domestic electric circuits
Okay, so let's talk about the wiring in our homes.
- • Live wire: red insulation; Neutral wire: black insulation
- • Potential difference between live and neutral = 220 V
- • Earth wire: green insulation, connected deep into earth (safety)
- • 15 A circuit for high-power appliances; 5 A circuit for bulbs/fans
- • Appliances connected in parallel (equal potential difference)
- • Short-circuit: sudden current increase; fuse melts to protect circuit
Summary
Okay, so let's look back at everything we covered in this chapter. We started with Oersted, and his deflecting compass needle — that's what first showed us a current always produces a magnetic field around it. Then we looked at magnetic field lines. Around a straight wire, they're concentric circles, and we find their direction with the Right-Hand Thumb Rule. We also saw the field around a circular loop, and around a solenoid — remember, a solenoid behaves like a bar magnet, and that's how we make an electromagnet. Then came a new idea — a current-carrying conductor, placed in a magnetic field, feels a force. We find its direction using Fleming's Left-Hand Rule, and this is the working principle of the electric motor, with its split-ring commutator. After that, we moved to electromagnetic induction, discovered by Faraday — a changing magnetic field induces a current in a coil, and its direction comes from Fleming's Right-Hand Rule. This is the principle behind the electric generator, which gives AC or DC depending on whether it uses rings or a split-ring commutator. And finally, we saw how our homes get power safely, through live, neutral and earth wires, along with fuses. So, tell me — out of all this, which idea felt the most interesting to you?
AskMedha · Medha Ma’am — Bihar Board Class 10 Science, Chapter 13. Written from the textbook, checked twice.
Questions parents and students ask
- How do I get the "Magnetic Effects of Electric Current" notes as a PDF?
- Press "Save as PDF" — the phone’s print sheet opens; choose "Save as PDF" there. The PDF holds the notes only.
- Where are these notes written from?
- From the chapter’s own textbook text, part by part, in the book’s own terms; a second, independent model then checked every part against the book. The full lesson, a check question for each part and the practice are in the AskMedha app.
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