Quick answer: Three hand rules are used in magnetic effects of current. The right-hand thumb rule gives the direction of the magnetic field around a current (thumb = current, curled fingers = field). Fleming's left-hand rule gives the force on a current-carrying conductor in a magnetic field (forefinger = field, middle finger = current, thumb = force). Fleming's right-hand rule gives the direction of induced current when a conductor moves in a field.
Syllabus note: The rationalised NCERT Class 10 book keeps the right-hand thumb rule and Fleming's left-hand rule. Electromagnetic induction, the electric generator and Fleming's right-hand rule were removed, along with the detailed working of the electric motor. The right-hand rule section below is for reference only.
The three rules at a glance
| Rule | Hand | What it finds | Used for |
|---|---|---|---|
| Right-hand thumb rule | Right | Direction of the magnetic field around a current | Straight wire, loop, solenoid |
| Fleming's left-hand rule | Left | Direction of force on a current-carrying conductor | Motor effect |
| Fleming's right-hand rule | Right | Direction of induced current | Generator (not in current Class 10 syllabus) |
Rule 1: right-hand thumb rule
Statement: Imagine holding a straight current-carrying conductor in your right hand so that the thumb points in the direction of the current. Then your fingers wrap around the conductor in the direction of the magnetic field lines.
current ↑ (thumb)
___|___
/ | \ field lines
| | | go round the
\___|___/ wire
|
- Current flowing upwards (towards you, seen from above): field lines go anticlockwise.
- Current flowing downwards (away from you): field lines go clockwise.
This rule is also called Maxwell's corkscrew rule in some books.
Rule 2: Fleming's left-hand rule
Statement: Stretch the thumb, forefinger and middle finger of your left hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the middle finger in the direction of the current, the thumb points in the direction of the force (motion) on the conductor.
| Finger | Shows |
|---|---|
| Forefinger | Magnetic field |
| Middle finger | Current |
| Thumb | Force (motion) |
Memory aid: Forefinger – Field; Centre (middle) finger – Current; thumb – thrust (force).
Devices such as electric motors and loudspeakers use this force.
Rule 3: Fleming's right-hand rule (for reference)
Statement: Stretch the thumb, forefinger and middle finger of your right hand so that they are mutually perpendicular. If the forefinger points in the direction of the magnetic field and the thumb in the direction of motion of the conductor, the middle finger gives the direction of the induced current.
This rule applies to electromagnetic induction (generators), which is not in the rationalised Class 10 syllabus.
Comparison table
| Feature | Right-hand thumb rule | Fleming's left-hand rule | Fleming's right-hand rule |
|---|---|---|---|
| Hand | Right | Left | Right |
| Thumb shows | Current | Force / motion | Motion of conductor |
| Forefinger shows | — | Magnetic field | Magnetic field |
| Middle finger shows | — | Current | Induced current |
| Curled fingers show | Magnetic field | — | — |
Exam tips
- Learn the exact wording of the right-hand thumb rule and Fleming's left-hand rule; both are asked as definitions.
- Remember: left hand for force (motor effect), right hand for the field around a current.
- For electron-beam questions, first reverse the direction to get the conventional current.
- Show the three fingers at right angles in a quick sketch if asked to explain the rule.
Common mistakes
- Using the left hand for the field around a wire.
- Mixing up the forefinger (field) and middle finger (current) in Fleming's left-hand rule.
- Using electron flow instead of conventional current.
- Spending time on Fleming's right-hand rule for a Class 10 exam; it is no longer in the syllabus.
Frequently Asked Questions
What is the right-hand thumb rule?
Hold a current-carrying wire in your right hand with the thumb pointing along the current. Your curled fingers show the direction of the magnetic field lines around the wire.
What is Fleming's left-hand rule?
Stretch the thumb, forefinger and middle finger of the left hand at right angles. If the forefinger shows the field and the middle finger the current, the thumb shows the force on the conductor.
What is the difference between Fleming's left-hand and right-hand rules?
The left-hand rule gives the direction of force on a current-carrying conductor (motor effect). The right-hand rule gives the direction of induced current in a moving conductor (generator effect).
Is Fleming's right-hand rule in the Class 10 syllabus?
No. Electromagnetic induction and Fleming's right-hand rule were removed from the rationalised NCERT Class 10 book.
What is Maxwell's corkscrew rule?
It is another way of stating the right-hand thumb rule: if a corkscrew is driven in the direction of the current, its turning direction gives the direction of the magnetic field.