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Magnetic effects of current is short, but it trips students up because it asks for directions in three dimensions on a flat page. Which way does the field point around a wire? Which way does a wire move in a magnet? This post gives you the two hand rules with worked examples, a domestic circuit calculation, the syllabus change for 2026-27, and a practice routine.
What does the syllabus include this year?
The CBSE Class X Science syllabus for 2026-27 lists: magnetic field and field lines, the field due to a current-carrying conductor, coil and solenoid, the force on a current-carrying conductor, Fleming's left-hand rule, direct and alternating current, the frequency of AC, and domestic electric circuits. In a box, it says the motor, electromagnetic induction and the electric generator are included but "will be assessed only formatively", which means through class activities rather than the year-end paper. Ask your teacher how your school handles these. The content below is from Chapter 12 of the NCERT Class 10 Science textbook.
What do magnetic field lines tell you?
NCERT defines a field line as the path a free north pole would tend to follow. Four facts carry most marks:
Outside a magnet, field lines go from the north pole to the south pole; inside, from south to north, so they form closed loops.
Lines are closer together where the field is stronger.
No two field lines cross. If they did, a compass at the crossing would point two ways at once.
Around a straight current-carrying wire, the lines are concentric circles. Inside a long solenoid they are parallel straight lines, so the field is uniform there.
A solenoid's field looks like a bar magnet's. With a soft iron core inside, it becomes an electromagnet.
How do you use the right-hand thumb rule?
Hold the wire in your right hand with your thumb along the current. Your fingers curl in the direction of the magnetic field.
Worked example. A vertical wire carries current upwards. What is the field direction at a point just east of the wire? Point your right thumb up. Your fingers curl anticlockwise when seen from above. Moving anticlockwise, a point to the east is heading north. So the field there points north. A compass placed at that spot would turn its north end northwards; a compass to the west would turn its north end southwards.
How do you use Fleming's left-hand rule?
Stretch the thumb, forefinger and middle finger of your left hand at right angles to each other. The forefinger points along the field, the middle finger along the current, and the thumb gives the force (the motion) on the conductor. NCERT notes the force is largest when current and field are at right angles.
Worked example. A horizontal wire carries current towards the east in a magnetic field pointing north. Forefinger north, middle finger east: your thumb points up. The wire is pushed upwards. Reverse either the current or the field and the force reverses.
For a moving charge, remember that the direction of current is opposite to the motion of electrons. NCERT's Example 12.2 uses this: an electron moving one way counts as a current the other way.
How does a domestic circuit protect you?
NCERT describes the Indian supply as 220 V AC at 50 Hz. The live wire (red insulation in NCERT's description), the neutral wire (black) and the earth wire (green) enter through a main fuse and meter. Homes often have a 15 A circuit for high-power appliances such as geysers and a 5 A circuit for bulbs and fans. Appliances are connected in parallel so each gets the same potential difference. The earth wire gives a low-resistance path, so a leak to an appliance's metal body does not give the user a severe shock.
Worked example (from the chapter's questions). A 2 kW electric oven is used on a 220 V circuit rated at 5 A. What happens? Current I = P/V = 2000/220 ≈ 9.1 A. That is more than the 5 A rating, so the fuse melts and breaks the circuit. This is overloading. A short circuit, where live and neutral touch, also causes a sudden rise in current.
Why is this chapter hard for so many students?
Electricity and magnetism is hard even at university. Maloney and colleagues (2001) built the Conceptual Survey of Electricity and Magnetism and gave it to more than 5,000 introductory physics students at 30 institutions. Before their courses, students averaged 25 to 31 per cent correct; after, only 44 to 47 per cent. Directions and fields are the kind of idea that needs repeated practice with feedback, not one reading.
Common Class 10 slips:
Using the right hand for force on a wire. Force uses the left hand; the field around a wire uses the right thumb rule.
Drawing field lines that cross or that stop in mid-air.
Forgetting electron direction. Electron flow is opposite to conventional current.
Saying a fuse goes in parallel. It is in series with the circuit it protects.
A practice routine for this chapter
Draw field lines for a bar magnet, a straight wire, a circular loop and a solenoid from memory. Check them against NCERT.
Do eight direction questions: four with the thumb rule, four with Fleming's rule. Sketch the three arrows each time.
Do five fuse questions: find each appliance's current using I = P/V and compare it with the circuit rating.
Explain, in three sentences, why the earth wire matters.
If you find it hard to imagine field lines around a coil, seeing them change as the current changes helps. The Fermi Simulation Lab has interactive simulations for ideas that are easier to see than read. If Ohm's law or power feels shaky, revise electricity in Class 10 first.
Before your next class, draw the field around a solenoid and mark which end acts as the north pole.
