🧲 Magnetic Effects of Electric Current
Magnetic Field Due to a Current-Carrying Conductor
धारावाही चालक के कारण चुंबकीय क्षेत्र
Class 10 Science | CBSE + Foundation + Competitive
🧲 Magnetic Field Due to a Current-Carrying Conductor
When electric current flows through a conductor, it produces a magnetic field around the conductor. This phenomenon is called the magnetic effect of electric current.
जब किसी चालक में विद्युत धारा प्रवाहित होती है, तो उसके चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है। इसे विद्युत धारा का चुंबकीय प्रभाव कहा जाता है।
This was demonstrated experimentally by Hans Christian Oersted.
Oersted observed that a compass needle placed near a current-carrying wire gets deflected. When the current direction is reversed, the compass deflection also reverses.
ओर्स्टेड ने देखा कि धारावाही तार के पास रखी कम्पास सुई विक्षेपित हो जाती है। जब धारा की दिशा बदल दी जाती है, तो कम्पास के विक्षेप की दिशा भी बदल जाती है।
For a straight current-carrying conductor, magnetic field lines are concentric circles around the conductor.
सीधे धारावाही चालक के चारों ओर चुंबकीय क्षेत्र रेखाएँ समकेन्द्रीय वृत्तों के रूप में होती हैं।
The direction of magnetic field around a straight current-carrying conductor can be determined by the Right-Hand Thumb Rule.
सीधे धारावाही चालक के चारों ओर चुंबकीय क्षेत्र की दिशा दाहिने हाथ के अंगूठा नियम से निर्धारित की जा सकती है।
👍 Thumb → Direction of conventional current
🌀 Curled fingers → Direction of magnetic field
याद रखें:
अंगूठा → धारा
मुड़ी हुई उँगलियाँ → चुंबकीय क्षेत्र
If the direction of current is reversed, the direction of the magnetic field also reverses.
यदि धारा की दिशा उलट दी जाए, तो चुंबकीय क्षेत्र की दिशा भी उलट जाती है।
↓
Magnetic Field
One Direction
↓
Magnetic Field
Reverses
For a straight conductor, increasing the current generally increases the magnetic field strength at a given distance from the conductor.
एक सीधे चालक में समान दूरी पर धारा बढ़ाने से सामान्यतः चुंबकीय क्षेत्र की तीव्रता बढ़ती है।
B = μ₀ I / (2πr)
Where:
- B = magnetic field
- μ₀ = permeability of free space
- I = current
- r = distance from conductor
B ∝ I
and
B ∝ 1/r
Thus, greater current → stronger field, while greater distance → weaker field.
The magnetic field due to a long straight conductor decreases as the distance from the conductor increases.
चालक से दूरी बढ़ने पर चुंबकीय क्षेत्र की तीव्रता कम होती जाती है।
↓
Stronger Field
↓
Weaker Field
| Condition | Magnetic Field |
|---|---|
| Current increases | Field strength increases at the same distance |
| Current decreases | Field strength decreases at the same distance |
| Distance increases | Field strength decreases |
| Current direction reversed | Field direction reverses |
| Long straight conductor | Concentric circular field lines |
Given:
I = 5 A
r = 10 cm = 0.10 m
μ₀ = 4π × 10⁻⁷ T m/A
B = 1 × 10⁻⁵ T
Answer: 1 × 10⁻⁵ T
Double the current → Magnetic field doubles
Double the distance → Magnetic field becomes half
A compass behaves like a small magnet. When placed near a current-carrying conductor, it experiences the magnetic field produced by the current and its needle deflects.
कम्पास एक छोटे चुंबक की तरह व्यवहार करता है। धारावाही चालक के पास रखने पर चालक द्वारा उत्पन्न चुंबकीय क्षेत्र के कारण इसकी सुई विक्षेपित होती है।
↑
Field Strength ↑
↑
Field Strength ↓
Changes
Field Direction Reverses
| Parameter | Effect on Magnetic Field |
|---|---|
| Increase current | Magnetic field increases |
| Decrease current | Magnetic field decreases |
| Increase distance | Magnetic field decreases |
| Decrease distance | Magnetic field increases |
| Reverse current | Field direction reverses |
✅ It consists of concentric circles.
❌ Increasing distance increases magnetic field.
✅ Increasing distance decreases the field.
❌ Reversing current does not affect magnetic field direction.
✅ Reversing current reverses field direction.
❌ Thumb represents magnetic field in the right-hand thumb rule.
✅ Thumb represents current; curled fingers represent magnetic field.
Answer: A magnetic field is produced around the conductor.
Answer: He observed that a compass needle deflects when placed near a current-carrying conductor.
Answer: They are concentric circles centred on the conductor.
Answer: Thumb gives current direction and curled fingers give magnetic field direction.
Answer: The direction of the magnetic field reverses.
Answer: A compass is placed near a straight wire. When current flows through the wire, the compass needle deflects. Reversing current reverses the deflection, proving that current produces a magnetic field.
Answer: The field consists of concentric circular lines around the conductor. The direction depends on current direction and is determined by the right-hand thumb rule.
Answer: At a fixed distance, the magnetic field strength increases with current.
Answer: The magnetic field decreases with distance for a long straight conductor.
Answer: It detects the magnetic field direction by the deflection and alignment of its needle.
Answer: Hold the conductor with the right hand. Point the thumb along conventional current. The curled fingers show the magnetic field direction around the conductor.
Answer: Magnetic field increases with current and decreases with distance from the conductor.
Answer: Current produces a magnetic field. The compass needle is a small magnet, so it experiences the magnetic field and changes its direction.
Here B is magnetic field, I is current, r is distance and μ₀ is permeability of free space.
Answer: The direction of magnetic field is related to the direction of current by the right-hand thumb rule. If the current direction is reversed, the circular magnetic field direction also reverses.
Answer: For a long straight conductor at a fixed distance, B ∝ I. Therefore, if current is doubled, the magnetic field doubles; if current is halved, the field becomes half.
Answer: For a long straight conductor, B ∝ 1/r. Thus increasing the distance reduces the magnetic field. Doubling distance makes the field half, under the same ideal conditions.
Answer: Oersted's experiment established that electric current produces a magnetic effect. It provided an important experimental connection between electricity and magnetism.
Answer: For a long straight conductor in free space, the magnitude of magnetic field at distance r is represented by:
Hence B is directly proportional to current I and inversely proportional to distance r.
Answer: Place a straight conductor above a compass. When no current flows, the needle points along Earth's magnetic field. When current is switched on, the needle deflects. Reversing current reverses the deflection. This demonstrates that current produces a magnetic field.
Answer: The field consists of concentric circular lines centred on the conductor. Field strength depends on current and distance. The direction is determined by the right-hand thumb rule.
Answer: Since B ∝ I:
Therefore the magnetic field becomes twice its original value.
Answer: Since B ∝ 1/r, doubling the distance makes the magnetic field half.
Answer: The magnetic field produced by a straight current-carrying conductor has the same magnitude at points at the same distance from the conductor, producing concentric circular field patterns.
Answer: Conventional current is taken to flow from positive terminal to negative terminal through the external circuit. The right-hand thumb rule uses this conventional current direction.
| Current Direction | Magnetic Field Direction |
|---|---|
| Along the conductor. | Circles around the conductor. |
| Represented by conventional current direction. | Determined by right-hand thumb rule. |
Answer: For a long straight conductor, B ∝ 1/r. Therefore, as distance increases, magnetic field strength decreases.
Answer: Place a compass near the conductor and mark the direction of the needle. Move the compass to different positions and repeat. Joining the marked directions smoothly gives the magnetic field-line pattern.
Answer: For a long straight conductor:
Thus B increases linearly with current and decreases inversely with distance. Reversing current changes field direction but not the magnitude for the same current magnitude and distance.
Answer: Electric current produces a magnetic field around a conductor. This principle is fundamental to electromagnets, electric motors, generators, relays, loudspeakers and many electrical devices.
Reason: Moving electric charges are associated with magnetic effects.
Reason: The field has circular symmetry around a long straight conductor.
Reason: B ∝ I for a long straight conductor.
Reason: B ∝ 1/r.
Reason: Magnetic field direction depends on current direction.
B₂/B₁ = (2I)/(2r) = 1.
Therefore the magnitude remains the same under the ideal long-straight-conductor relation.
r = 0.20 m
B = μ₀I/2πr
B = (4π × 10⁻⁷ × 10)/(2π × 0.20)
B = 1 × 10⁻⁵ T
B₂/B₁ = 12/4 = 3
New magnetic field = 3B
B₂/B₁ = r/3r = 1/3
New field = B/3
✔ Oersted demonstrated the magnetic effect of current.
✔ A compass needle deflects near a current-carrying conductor.
✔ Magnetic field around a straight conductor consists of concentric circles.
✔ Right-hand thumb rule gives field direction.
✔ Thumb → current direction.
✔ Curled fingers → magnetic field direction.
✔ B ∝ I.
✔ B ∝ 1/r.
✔ Reversing current reverses magnetic field direction.
✔ For a long straight conductor: B = μ₀I/2πr.
👍 Thumb = Current
🌀 Fingers = Magnetic Field
📈 Current ↑ → B ↑
📏 Distance ↑ → B ↓
🔄 Current Reverse → Field Reverse
⭕ Straight Wire → Circular Field Lines
1. Current-carrying conductor produces magnetic field.
2. Oersted observed compass deflection.
3. Straight conductor → concentric circular field lines.
4. Right-hand thumb rule determines field direction.
5. B ∝ I.
6. B ∝ 1/r.
7. Reverse current → reverse field direction.
8. B = μ₀I/2πr for a long straight conductor in free space.
↓
Magnetic Effect
↓
Magnetic Field
↓
Concentric Circles
↓
Right-Hand Thumb Rule
↓
B ↑
↓
B ↓
A current-carrying conductor produces a magnetic field around itself. The magnetic effect of electric current was demonstrated by Oersted through the deflection of a compass needle near a current-carrying wire.
For a long straight conductor, the magnetic field lines are concentric circles around the conductor. The direction of these field lines is determined using the right-hand thumb rule.
For a long straight conductor in free space, the magnetic field is given by:
Therefore, the magnetic field increases with current and decreases with distance. If the current direction is reversed, the magnetic field direction also reverses.
Magnetic Effects of Electric Current
Magnetic Field Due to a Current-Carrying Conductor
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