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What is the right-hand thumb rule?

Class 10 ScienceNCERT chapter: Magnetic Effects of Electric Currentइसे हिंदी में पढ़ें

Exam-ready answer

The right-hand thumb rule gives the direction of the magnetic field around a straight current-carrying conductor. Hold the conductor in your right hand with the thumb pointing along the current; then your curled fingers give the direction of the magnetic field lines around the conductor.

Explanation

When electric current flows through a straight conductor, a magnetic field is produced around it. The field lines are concentric circles in a plane perpendicular to the conductor. The right-hand thumb rule helps us quickly find the direction of these circular field lines without using a compass.

To apply the rule: imagine holding the current-carrying straight wire in your right hand. Your thumb should point in the direction of the conventional current (from positive to negative). Your curled fingers then wrap around the wire in the direction of the magnetic field lines.

For example, if current flows vertically upward in a wire, the magnetic field lines around it will be anticlockwise when viewed from above. This rule is also called Maxwell's corkscrew rule. It is used for straight conductors, while the right-hand grip rule is used for solenoids.

Points to remember

  1. Right-hand thumb rule: thumb → direction of current, curled fingers → direction of magnetic field.
  2. Applies to a straight current-carrying conductor.
  3. Magnetic field lines are concentric circles around the conductor.
  4. The rule gives only the direction, not the magnitude of the magnetic field.
  5. Also known as Maxwell's corkscrew rule.

Exam tip

While writing the answer, draw a neat labelled diagram showing a straight conductor, the direction of current (I), and the circular magnetic field lines with arrows. Mention that the thumb points along the current and curled fingers give the field direction.

Questions students also ask

What is the difference between right-hand thumb rule and Fleming's left-hand rule?
The right-hand thumb rule gives the direction of the magnetic field around a current-carrying straight conductor. Fleming's left-hand rule gives the direction of force on a current-carrying conductor placed in a magnetic field.
Can the right-hand thumb rule be used for a circular loop?
No, the right-hand thumb rule is specifically for a straight conductor. For a circular loop, you can use the right-hand thumb rule at each small segment, but the overall field is found by summing the contributions.
What is the direction of the magnetic field if current flows from south to north?
If current flows from south to north (upward), then using the right-hand thumb rule, the magnetic field lines will be anticlockwise when viewed from above the wire.

Chapter labels help you find the topic in your textbook. Check your own edition: chapter names and order can change. These are Know.it explanations, not official NCERT solutions.