Right-hand thumb rule
- CBSE · NCERT Class 10, Ch 12 Magnetic Effects of Electric Current
The right-hand thumb rule finds the direction of the magnetic field around a current-carrying wire: thumb along the current, fingers curl along the field.
Imagine holding the wire in your right hand, with your thumb pointing the way the current flows. Your fingers wrap round the wire. The way they curl is the direction of the magnetic field lines. NCERT also calls it Maxwell's corkscrew rule.
Reverse the current and the thumb turns round. The fingers then curl the other way, so the field reverses too. The rule also works for a loop and a solenoid.
A small example
A wire stands upright through a card, and 2 A flows upward in it. Point your right thumb up. Seen from above, your fingers curl anticlockwise. So a compass on the card points anticlockwise round the wire. Send the 2 A downward instead, and it points clockwise.
Where marks go
Question 36(A) of CBSE's 2026-27 Science sample paper asks you to state the rule and describe how it finds the field's direction. The 2026-27 Science marking scheme gives 1 mark for the statement and 1 for the use. The statement names the right hand, the thumb along the current and the fingers along the field.
Question 38 of the same paper, in its version for visually impaired students, gives 2 marks for using the rule. It asks why a compass swings the other way when the current reverses. Read how step marking works.
Sources
Facts last checked against these sources on 30 September 2026.
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