🧲 Magnetic Effects of Electric Current
Right-Hand Thumb Rule
दाहिने हाथ के अंगूठे का नियम
Class 10 Science | CBSE + Foundation + Competitive
🧲 Right-Hand Thumb Rule | दाहिने हाथ के अंगूठे का नियम
The Right-Hand Thumb Rule is used to determine the direction of the magnetic field around a straight current-carrying conductor.
दाहिने हाथ के अंगूठे का नियम सीधे धारावाही चालक के चारों ओर उत्पन्न चुंबकीय क्षेत्र की दिशा ज्ञात करने के लिए प्रयोग किया जाता है।
It gives the relationship between the direction of conventional current and the direction of the circular magnetic field around the conductor.
If we hold a straight current-carrying conductor in our right hand with the thumb pointing in the direction of conventional current, then the curled fingers give the direction of the magnetic field around the conductor.
हिंदी में:
यदि किसी सीधे धारावाही चालक को दाहिने हाथ में इस प्रकार पकड़ें कि अंगूठा पारंपरिक धारा की दिशा में हो, तो मुड़ी हुई उँगलियाँ चालक के चारों ओर चुंबकीय क्षेत्र की दिशा बताती हैं।
Right hand से conductor को पकड़ें।
Thumb को conventional current की दिशा में रखें।
Curled fingers magnetic field की दिशा बताएँगी।
Suppose the conventional current flows upward through a vertical conductor. Point your right thumb upward. Your curled fingers show the direction of the magnetic field around the wire.
यदि पारंपरिक धारा ऊर्ध्व दिशा में बह रही है, तो दाहिने हाथ का अंगूठा ऊपर की ओर रखें। मुड़ी हुई उँगलियाँ चुंबकीय क्षेत्र की दिशा बताएँगी।
If the current direction is reversed, point your right thumb downward. The curled fingers now show the magnetic field in the opposite direction.
यदि धारा की दिशा नीचे कर दी जाए, तो अंगूठे को नीचे की ओर रखने पर मुड़ी हुई उँगलियाँ चुंबकीय क्षेत्र की विपरीत दिशा बताएँगी।
↓
Field Direction A
↓
Field Direction B
(Opposite)
For a conductor perpendicular to the plane of the paper:
- If current comes out of the page, the magnetic field is anticlockwise.
- If current goes into the page, the magnetic field is clockwise.
| Symbol | Meaning | Magnetic Field Direction |
|---|---|---|
| ⊙ | Current coming out of the page | Anticlockwise |
| ⊗ | Current going into the page | Clockwise |
Dot (•) = arrowhead coming towards you → current out of page.
Cross (×) = tail/feathers of an arrow going away from you → current into page.
| Current | Magnetic Field |
|---|---|
| Along the conductor | Forms circular paths around conductor |
| Shown by thumb | Shown by curled fingers |
| Reversal changes current direction | Field direction also reverses |
The right-hand thumb rule gives the direction of the magnetic field. The magnitude for a long straight conductor in free space is given by:
Therefore:
Answer: Anticlockwise when viewed from above.
Answer: Magnetic field direction reverses.
The fingers curl anticlockwise.
Answer: Anticlockwise.
✅ Thumb shows conventional current direction.
❌ Fingers show current direction.
✅ Curled fingers show magnetic field direction.
❌ Reversing current keeps field direction unchanged.
✅ Reversing current reverses field direction.
❌ Dot means current going into the page.
✅ Dot means current coming out of the page.
❌ Cross means current coming out of the page.
✅ Cross means current going into the page.
Answer: It determines the direction of magnetic field around a straight current-carrying conductor.
Answer: The thumb represents the direction of conventional current.
Answer: They represent the direction of magnetic field.
Answer: The magnetic field direction is reversed.
Answer: Current coming out of the plane of the page.
Answer: Hold the conductor in the right hand with the thumb pointing along conventional current. The curled fingers show the magnetic field direction.
Answer: It represents current going into the plane of the page.
Answer: Anticlockwise.
Answer: Clockwise.
Answer: The magnetic field direction is determined by current direction. Hence reversing current reverses the field direction.
Answer: If current flows upward in a straight wire, point the right thumb upward. The curled fingers show the circular magnetic field direction around the wire.
| Dot (⊙) | Cross (⊗) |
|---|---|
| Current out of page | Current into page |
| Field anticlockwise | Field clockwise |
Answer: Current direction determines the sense of circular magnetic field around the conductor. Reversing current reverses the magnetic field direction.
Answer: It provides a simple method for determining the direction of magnetic field around a current-carrying straight conductor.
Answer: The thumb points in conventional current direction and the curled fingers show magnetic field direction. The field lines are concentric circles around the conductor.
Answer: Point the right thumb towards yourself. The fingers curl anticlockwise. Therefore the magnetic field is anticlockwise.
Answer: Point the right thumb away from yourself. The fingers curl clockwise. Therefore the magnetic field is clockwise.
Answer: The right-hand thumb rule can be used in reverse. If the circular field direction is known, curl the fingers in that direction; the thumb then gives the conventional current direction.
Answer: The rule determines magnetic field direction around a straight current-carrying conductor. It is useful in analysing magnetic field patterns, determining clockwise/anticlockwise direction and understanding electromagnetic devices.
Answer: When the current direction is reversed, the thumb direction must also be reversed. Consequently, the curled fingers reverse their direction. Hence the magnetic field direction reverses.
Answer: Dot represents a vector coming out of the page, while cross represents a vector going into the page. For a current-carrying straight conductor, dot corresponds to anticlockwise field and cross corresponds to clockwise field.
Answer: It is the assumed direction of current from the positive terminal to the negative terminal through the external circuit.
Answer: No. It gives the direction. For a long straight conductor, magnitude is given by B = μ₀I/2πr.
Answer: Point the right thumb in the current direction. The curled fingers give the magnetic field direction.
Answer: By the right-hand thumb rule, the thumb points out of the page. Therefore the conventional current is coming out of the page.
Answer: The current is directed into the page.
Answer: Hold the conductor with the right hand. When thumb points upward, fingers curl in one circular direction around the conductor. If thumb points downward, the fingers curl in the opposite direction.
Answer: The field has circular symmetry around the straight conductor. Points at equal perpendicular distances have the same field magnitude, producing concentric circular field lines.
Answer: The first reversal reverses the field direction. The second reversal brings it back to its original direction, provided the current magnitude and geometry are unchanged.
Answer: A current-carrying straight conductor produces circular magnetic field lines. The right-hand thumb rule determines their direction: thumb indicates conventional current and curled fingers indicate magnetic field. Reversing current reverses the field direction. Dot and cross notation can represent current out of and into the page respectively.
Reason: The magnetic field direction is related to the direction of conventional current.
Reason: The curled fingers must reverse when the thumb direction reverses.
Reason: Curled fingers represent current direction.
Reason: The right thumb points towards the observer.
Reason: Cross denotes current entering the page.
✔ Thumb → Conventional current.
✔ Curled fingers → Magnetic field.
✔ Straight conductor → Circular magnetic field lines.
✔ Current out of page → Anticlockwise field.
✔ Current into page → Clockwise field.
✔ Reverse current → Reverse magnetic field direction.
✔ Dot (⊙) → Out of page.
✔ Cross (⊗) → Into page.
✔ Right-Hand Thumb Rule gives direction, not directly the magnitude.
👍 Thumb = Current
🌀 Fingers = Field
OUT → ANTI
Current OUT of page → Anticlockwise
IN → CLOCK
Current IN to page → Clockwise
I ↑ → B ↑
r ↑ → B ↓
1. Current-carrying conductor produces magnetic field.
2. Straight conductor has circular magnetic field lines.
3. Right thumb gives conventional current direction.
4. Curled fingers give magnetic field direction.
5. Current out of page → anticlockwise.
6. Current into page → clockwise.
7. Reverse current → reverse field.
8. B ∝ I.
9. B ∝ 1/r.
↓
Magnetic Field
↓
Circular Field
↓
Current
↓
Magnetic Field
↓
Anticlockwise
↓
Clockwise
The Right-Hand Thumb Rule is a simple method for determining the direction of magnetic field around a straight current-carrying conductor.
When the right-hand thumb points in the direction of conventional current, the curled fingers show the direction of the magnetic field.
For current coming out of the page, the magnetic field is anticlockwise. For current going into the page, the magnetic field is clockwise.
For a long straight conductor, the magnitude of magnetic field is:
Thus, the direction is determined by the right-hand thumb rule, while the magnitude depends on current and distance.
Magnetic Effects of Electric Current
Right-Hand Thumb Rule
दाहिने हाथ के अंगूठे का नियम
CBSE • Foundation • Competitive Preparation
