Magnetic Effects of Electric Current
Solenoid and Its Magnetic Field
सोलनॉइड तथा उसका चुंबकीय क्षेत्र
Class 10 Science | CBSE + Foundation + Competitive
Solenoid and Its Magnetic Field
1. Introduction | परिचय
English:
A solenoid is a long cylindrical coil consisting of a large number of closely wound turns of insulated conducting wire. When electric current passes through a solenoid, it produces a magnetic field around it.
हिन्दी:
सोलनॉइड एक लंबी बेलनाकार कुंडली होती है, जिसमें विद्युतरोधी चालक तार के बहुत सारे पास-पास लपेटे हुए फेरे होते हैं। जब सोलनॉइड में विद्युत धारा प्रवाहित की जाती है, तो उसके चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है।
A solenoid is a long cylindrical coil consisting of a large number of closely wound turns of insulated conducting wire. When electric current passes through a solenoid, it produces a magnetic field around it.
हिन्दी:
सोलनॉइड एक लंबी बेलनाकार कुंडली होती है, जिसमें विद्युतरोधी चालक तार के बहुत सारे पास-पास लपेटे हुए फेरे होते हैं। जब सोलनॉइड में विद्युत धारा प्रवाहित की जाती है, तो उसके चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है।
2. Structure of a Solenoid | सोलनॉइड की संरचना
A solenoid generally consists of:
1. Long cylindrical arrangement
2. Large number of turns
3. Insulated conducting wire
4. Current supplied through the coil
5. It may contain a soft iron core when a strong electromagnet is required.
सोलनॉइड में तार के बहुत से पास-पास फेरे होते हैं। आवश्यकता के अनुसार इसके अंदर नरम लोहे का कोर भी रखा जा सकता है।
1. Long cylindrical arrangement
2. Large number of turns
3. Insulated conducting wire
4. Current supplied through the coil
5. It may contain a soft iron core when a strong electromagnet is required.
सोलनॉइड में तार के बहुत से पास-पास फेरे होते हैं। आवश्यकता के अनुसार इसके अंदर नरम लोहे का कोर भी रखा जा सकता है।
3. Animated Diagram of Solenoid
Orange = Current-carrying turns | Blue = Magnetic field
4. Magnetic Field Pattern of a Solenoid
The magnetic field produced by a current-carrying solenoid resembles the magnetic field of a bar magnet.
Inside a sufficiently long solenoid, the magnetic field lines are nearly parallel and equally spaced.
Therefore, the magnetic field inside a long solenoid is approximately uniform.
हिन्दी:
धारा-वाहक सोलनॉइड का चुंबकीय क्षेत्र बार मैग्नेट के चुंबकीय क्षेत्र के समान होता है। लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र रेखाएँ लगभग समानांतर और समान दूरी पर होती हैं। इसलिए अंदर का चुंबकीय क्षेत्र लगभग एकसमान होता है।
हिन्दी:
धारा-वाहक सोलनॉइड का चुंबकीय क्षेत्र बार मैग्नेट के चुंबकीय क्षेत्र के समान होता है। लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र रेखाएँ लगभग समानांतर और समान दूरी पर होती हैं। इसलिए अंदर का चुंबकीय क्षेत्र लगभग एकसमान होता है।
5. Uniform Magnetic Field | एकसमान चुंबकीय क्षेत्र
A magnetic field is called approximately uniform when its magnitude and direction are nearly the same throughout a region.
Inside a long solenoid, the field lines are nearly parallel and equally spaced.
लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र लगभग एकसमान होता है क्योंकि वहाँ क्षेत्र रेखाएँ लगभग समानांतर तथा समान दूरी पर होती हैं।
लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र लगभग एकसमान होता है क्योंकि वहाँ क्षेत्र रेखाएँ लगभग समानांतर तथा समान दूरी पर होती हैं।
6. Magnetic Field Due to a Long Solenoid
Magnetic Field inside a long solenoid:
B = μ₀ n I
Where:
B = Magnetic field
μ₀ = Permeability of free space
n = Number of turns per unit length
I = Current through solenoid
B = μ₀ n I
Where:
B = Magnetic field
μ₀ = Permeability of free space
n = Number of turns per unit length
I = Current through solenoid
If the solenoid has N turns and length L:
n = N/L
Therefore:
B = μ₀(N/L)I
B = μ₀NI/L
This relation applies to an ideal/long solenoid in free space or approximately in air.
B = μ₀NI/L
7. Number of Turns per Unit Length
The number of turns per unit length is represented by n.
N = Total number of turns
L = Length of solenoid
n = Turns per metre
n = N/L
Here:
N = Total number of turns
L = Length of solenoid
n = Turns per metre
Important:
More turns per unit length → stronger magnetic field.
अधिक turns per unit length → अधिक प्रबल चुंबकीय क्षेत्र।
More turns per unit length → stronger magnetic field.
अधिक turns per unit length → अधिक प्रबल चुंबकीय क्षेत्र।
8. Factors Affecting Magnetic Field of a Solenoid
| Factor | Effect on Magnetic Field |
|---|---|
| Current I increases | B increases |
| Turns per unit length n increases | B increases |
| Current direction reverses | Magnetic field direction reverses |
| Suitable soft iron core is inserted | Field becomes much stronger |
9. Solenoid as a Bar Magnet
A current-carrying solenoid behaves like a bar magnet.
It has two magnetic poles:
North Pole (N)
South Pole (S)
Outside the solenoid, magnetic field lines emerge from the North pole and enter the South pole. Inside the magnet/solenoid, the field lines complete the closed path.
हिन्दी:
धारा-वाहक सोलनॉइड बार मैग्नेट की तरह व्यवहार करता है और इसके दो ध्रुव होते हैं—उत्तर तथा दक्षिण।
North Pole (N)
South Pole (S)
Outside the solenoid, magnetic field lines emerge from the North pole and enter the South pole. Inside the magnet/solenoid, the field lines complete the closed path.
हिन्दी:
धारा-वाहक सोलनॉइड बार मैग्नेट की तरह व्यवहार करता है और इसके दो ध्रुव होते हैं—उत्तर तथा दक्षिण।
10. Finding Polarity of Solenoid
The polarity of a solenoid can be determined using the right-hand grip rule.
Curl the fingers of your right hand in the direction of current through the turns. The thumb points towards the North pole of the solenoid.
Right-Hand Grip Rule:
Fingers → Current
Thumb → North Pole / Magnetic field direction inside the solenoid
Right-Hand Grip Rule:
Fingers → Current
Thumb → North Pole / Magnetic field direction inside the solenoid
Easy Memory Trick:
Anticlockwise current as seen from a face → That face is North.
Clockwise current as seen from a face → That face is South.
Anticlockwise current as seen from a face → That face is North.
Clockwise current as seen from a face → That face is South.
11. Why is the Field Inside a Solenoid Nearly Uniform?
The magnetic fields produced by individual turns add together inside the solenoid.
For a long solenoid, the contributions combine in such a way that the field lines inside are nearly parallel and equally spaced.
Therefore, the magnetic field inside is approximately uniform.
12. Magnetic Field Outside a Long Solenoid
For an ideal long solenoid, the magnetic field outside is very weak compared with the field inside.
The field inside is therefore considered strong and approximately uniform, while outside it is much weaker.
लंबे आदर्श सोलनॉइड के बाहर चुंबकीय क्षेत्र अंदर की तुलना में बहुत कमजोर माना जाता है।
लंबे आदर्श सोलनॉइड के बाहर चुंबकीय क्षेत्र अंदर की तुलना में बहुत कमजोर माना जाता है।
13. Effect of Increasing Current
From:
B = μ₀nI
If n remains constant:
B ∝ I
Therefore, doubling current doubles the magnetic field.
14. Effect of Turns per Unit Length
From:
B = μ₀nI
Therefore:
B ∝ n
If the number of turns per unit length is doubled, the magnetic field also doubles, provided current remains constant.
15. Soft Iron Core in Solenoid
When a suitable soft iron core is placed inside a current-carrying solenoid, the magnetic field becomes much stronger.
The combination is called an electromagnet.
Soft iron is preferred because it magnetises strongly when current flows and loses most of its magnetism when current is removed.
हिन्दी:
सोलनॉइड के अंदर नरम लोहे का कोर रखने पर चुंबकीय क्षेत्र बहुत अधिक मजबूत हो जाता है। इस व्यवस्था को विद्युतचुंबक कहा जाता है।
हिन्दी:
सोलनॉइड के अंदर नरम लोहे का कोर रखने पर चुंबकीय क्षेत्र बहुत अधिक मजबूत हो जाता है। इस व्यवस्था को विद्युतचुंबक कहा जाता है।
16. Solenoid vs Bar Magnet
| Solenoid | Bar Magnet |
|---|---|
| Magnetism is produced by electric current. | Permanent magnetic behaviour is present. |
| Strength can be controlled by current and turns. | Strength is not normally controlled by simply switching current. |
| Can be switched ON/OFF. | Cannot simply be switched OFF. |
| Polarity can be reversed by reversing current. | Polarity does not reverse merely by changing an external current. |
17. Electromagnet
An electromagnet is a temporary magnet produced when electric current flows through a coil, usually around a soft iron core.
Applications:
• Electric bells
• Relays
• Electromagnetic cranes
• Loudspeakers
• Motors and other electrical devices
Applications:
• Electric bells
• Relays
• Electromagnetic cranes
• Loudspeakers
• Motors and other electrical devices
18. How to Make a Strong Electromagnet
A strong electromagnet can generally be obtained by:
✔ Increasing current
✔ Increasing number of turns per unit length
✔ Using a suitable soft iron core
✔ Keeping the coil arrangement compact and appropriate
✔ Increasing current
✔ Increasing number of turns per unit length
✔ Using a suitable soft iron core
✔ Keeping the coil arrangement compact and appropriate
19. Numerical Example
Question:
A long solenoid has 1000 turns distributed uniformly over a length of 0.5 m. It carries a current of 2 A. Calculate the magnetic field inside it in air.
Solution: N = 1000
L = 0.5 m
I = 2 A
n = N/L
n = 1000/0.5 = 2000 m⁻¹
B = μ₀nI
B = 4π × 10⁻⁷ × 2000 × 2
B = 16π × 10⁻⁴ T
Approximately: B ≈ 5.03 × 10⁻³ T
Solution: N = 1000
L = 0.5 m
I = 2 A
n = N/L
n = 1000/0.5 = 2000 m⁻¹
B = μ₀nI
B = 4π × 10⁻⁷ × 2000 × 2
B = 16π × 10⁻⁴ T
Approximately: B ≈ 5.03 × 10⁻³ T
20. 30 MCQs | बहुविकल्पीय प्रश्न
1. A solenoid is:
A. A single straight wire
B. A long coil of many turns
C. A battery
D. A resistor
Answer: B
2. A current-carrying solenoid produces:
A. Magnetic field
B. Only sound
C. Only light
D. No field
Answer: A
3. The magnetic field inside a long solenoid is approximately:
A. Zero
B. Uniform
C. Random
D. Circular only
Answer: B
4. Magnetic field inside a long solenoid is:
A. B = μ₀nI
B. B = μ₀I/n
C. B = n/μ₀I
D. B = μ₀/nI
Answer: A
5. Number of turns per unit length is:
A. n = L/N
B. n = NI
C. n = N/L
D. n = N+L
Answer: C
6. Increasing current in a solenoid:
A. Decreases B
B. Increases B
C. Makes B zero
D. Has no effect
Answer: B
7. Increasing turns per unit length:
A. Increases magnetic field
B. Decreases magnetic field
C. Makes field zero
D. Has no effect
Answer: A
8. The magnetic field of a solenoid resembles that of:
A. Capacitor
B. Bar magnet
C. Resistor
D. Battery
Answer: B
9. A solenoid can be used to make:
A. Electromagnet
B. Thermometer
C. Fuse only
D. Ammeter only
Answer: A
10. The SI unit of magnetic field is:
A. Ampere
B. Tesla
C. Volt
D. Ohm
Answer: B
11. The direction of polarity of a solenoid can be determined using:
A. Right-hand grip rule
B. Ohm's law
C. Joule's law
D. Snell's law
Answer: A
12. A suitable core used in an electromagnet is:
A. Soft iron
B. Wood
C. Plastic
D. Glass
Answer: A
13. If current is doubled, magnetic field becomes:
A. Half
B. Double
C. Four times
D. Zero
Answer: B
14. If turns per unit length are doubled, B becomes:
A. Half
B. Same
C. Double
D. Zero
Answer: C
15. If current direction is reversed, magnetic field direction:
A. Reverses
B. Remains same
C. Becomes zero
D. Becomes infinite
Answer: A
16. The field lines inside a long solenoid are:
A. Nearly parallel
B. Random
C. Circular around every point
D. Absent
Answer: A
17. Outside an ideal long solenoid, magnetic field is:
A. Very strong
B. Much weaker than inside
C. Always infinite
D. Equal everywhere
Answer: B
18. An electromagnet is generally:
A. Temporary magnet
B. Permanent magnet only
C. Non-magnetic object
D. Battery
Answer: A
19. Soft iron is used in electromagnets because it:
A. Is easily magnetised
B. Cannot be magnetised
C. Is transparent
D. Produces electricity itself
Answer: A
20. The field of a solenoid becomes stronger with:
A. More turns per unit length
B. Less current
C. Fewer turns
D. No current
Answer: A
21. If N = 500 and L = 0.5 m, n is:
A. 100 turns/m
B. 500 turns/m
C. 1000 turns/m
D. 250 turns/m
Answer: C
22. For a long solenoid, B depends on:
A. n and I
B. Only length
C. Only radius
D. Only resistance
Answer: A
23. If current becomes zero, ideal electromagnet loses its magnetic field:
A. Immediately/approximately
B. It becomes stronger
C. It becomes infinite
D. It doubles
Answer: A
24. Which rule identifies the north pole of a solenoid?
A. Right-hand grip rule
B. Fleming's left-hand rule
C. Ohm's law
D. Lens rule
Answer: A
25. The field inside a long solenoid is approximately:
A. Uniform
B. Zero
C. Non-existent
D. Completely random
Answer: A
26. If n and I are both doubled, B becomes:
A. Half
B. Double
C. Four times
D. Same
Answer: C
27. A solenoid has 2000 turns in 1 m. Its n is:
A. 200 turns/m
B. 2000 turns/m
C. 20 turns/m
D. 2 turns/m
Answer: B
28. Which material is generally preferred as an electromagnet core?
A. Soft iron
B. Rubber
C. Plastic
D. Paper
Answer: A
29. A solenoid has two magnetic poles:
A. North and South
B. East and West
C. Positive and negative
D. Hot and cold
Answer: A
30. A major advantage of an electromagnet is:
A. Its magnetism can be controlled
B. It cannot be switched
C. It always remains magnetic
D. It does not require current
Answer: A
21. 30 Subjective Questions with Answers
2 Marks
1. What is a solenoid?
A solenoid is a long cylindrical coil having a large number of closely wound turns of insulated conducting wire.
2 Marks
2. What happens when current passes through a solenoid?
A magnetic field is produced around the solenoid. The solenoid behaves like a bar magnet.
2 Marks
3. What is meant by number of turns per unit length?
It is the number of turns present per unit length of the solenoid.
n = N/L
2 Marks
4. Write the formula for magnetic field inside a long solenoid.
B = μ₀nI
2 Marks
5. Name the material generally used as core of an electromagnet.
Soft iron is generally used because it can be strongly magnetised and largely loses its magnetism when current is removed.
3 Marks
6. Why does a solenoid behave like a bar magnet?
A current-carrying solenoid produces a magnetic field pattern similar to a bar magnet and has two poles, North and South.
3 Marks
7. How can the polarity of a solenoid be determined?
Use the right-hand grip rule. Curl the fingers in the direction of current; the thumb points towards the North pole.
3 Marks
8. Why is the magnetic field inside a long solenoid nearly uniform?
The fields produced by the closely spaced turns add together. Inside a long solenoid, the resultant field lines are nearly parallel and equally spaced.
3 Marks
9. What happens to B when current is doubled?
Since B = μ₀nI and B ∝ I, doubling current doubles the magnetic field.
3 Marks
10. What happens to B when turns per unit length are doubled?
Since B ∝ n, doubling turns per unit length doubles the magnetic field.
4 Marks
11. Derive B = μ₀NI/L for a long solenoid.
For a long solenoid:
B = μ₀nI
But:
n = N/L
Therefore:
B = μ₀(N/L)I
Hence:
B = μ₀NI/L
4 Marks
12. Explain the right-hand grip rule.
Hold the solenoid with your right hand so that the curled fingers point in the direction of current through its turns. The thumb points towards the North pole of the solenoid.
4 Marks
13. What is an electromagnet?
An electromagnet is a temporary magnet produced by passing current through a coil, generally wound around a soft iron core.
4 Marks
14. Give three ways of increasing the strength of an electromagnet.
1. Increase current.
2. Increase number of turns per unit length.
3. Use a suitable soft iron core.
2. Increase number of turns per unit length.
3. Use a suitable soft iron core.
4 Marks
15. Distinguish between solenoid and electromagnet.
A solenoid is the coil of many turns of wire. When a suitable magnetic core such as soft iron is placed inside and current flows, the arrangement acts as a strong electromagnet.
5 Marks
16. Explain the factors affecting the magnetic field of a solenoid.
B = μ₀nI
Therefore:
• B increases with current I.
• B increases with turns per unit length n.
• Reversing current reverses field direction.
• A suitable soft iron core greatly strengthens the field.
• B increases with current I.
• B increases with turns per unit length n.
• Reversing current reverses field direction.
• A suitable soft iron core greatly strengthens the field.
5 Marks
17. Explain why soft iron is used in electromagnets.
Soft iron has high magnetic permeability and can become strongly magnetised in the presence of the magnetic field. It also loses most of its magnetism when the current is switched off, making it suitable for temporary magnets.
5 Marks
18. Compare magnetic field inside and outside a long solenoid.
Inside:
• Stronger
• Approximately uniform
• Field lines nearly parallel
Outside:
• Much weaker for an ideal long solenoid
• Field lines complete their closed paths outside
• Stronger
• Approximately uniform
• Field lines nearly parallel
Outside:
• Much weaker for an ideal long solenoid
• Field lines complete their closed paths outside
5 Marks
19. A solenoid has 500 turns and length 0.25 m. Find turns per metre.
n = N/L
n = 500/0.25
n = 2000 turns/m
n = 500/0.25
n = 2000 turns/m
5 Marks
20. A solenoid has 1000 turns, length 0.5 m and current 2 A. Calculate B in air.
B = μ₀NI/L
= (4π×10⁻⁷ ×1000×2)/0.5
B ≈ 5.03×10⁻³ T
= (4π×10⁻⁷ ×1000×2)/0.5
B ≈ 5.03×10⁻³ T
6 Marks
21. Explain the construction and working of an electromagnet.
A coil of insulated wire is wound around a suitable soft iron core. When current passes through the coil, the magnetic field of the coil magnetises the iron core. The combination becomes a strong magnet. When current is switched off, most of the magnetism disappears.
6 Marks
22. Explain why a solenoid is similar to a bar magnet.
Both have two magnetic poles and produce similar external magnetic field patterns. Magnetic field lines emerge from the north pole and enter the south pole outside. A current-carrying solenoid can therefore behave like a bar magnet.
6 Marks
23. What happens to magnetic field if current direction is reversed?
The polarity of the solenoid reverses. The North pole becomes South and the South pole becomes North. The magnetic field direction also reverses.
6 Marks
24. Why is a solenoid useful for producing a strong magnetic field?
A solenoid contains many closely spaced turns. The magnetic fields of individual turns add together inside the solenoid. Therefore, a strong and approximately uniform magnetic field can be obtained.
6 Marks
25. Explain the relation B = μ₀nI.
For a long solenoid, magnetic field is proportional to the number of turns per unit length and current. The proportionality constant in free space is μ₀.
Therefore:
B = μ₀nI
6 Marks
26. If the length of a solenoid is doubled while total number of turns remains the same, what happens to B?
n = N/L
If L is doubled while N remains constant, n becomes half.
Since:
B ∝ n
the magnetic field becomes half, assuming current remains unchanged.
6 Marks
27. If both N and L are doubled, what happens to B?
n = N/L
New:
n' = 2N/2L = N/L
Therefore n remains unchanged.
Hence, for the same current, B remains unchanged.
6 Marks
28. If current is doubled and length is also doubled while N remains constant, what happens to B?
B = μ₀NI/L
B'/B = (2I)/(2L) × L/I = 1.
Therefore, magnetic field remains unchanged.
6 Marks
29. Explain two advantages of an electromagnet over a permanent magnet.
1. An electromagnet can be switched ON and OFF by controlling current.
2. Its strength can be changed by changing current or number of turns.
3. Its polarity can be reversed by reversing current.
2. Its strength can be changed by changing current or number of turns.
3. Its polarity can be reversed by reversing current.
6 Marks
30. Write a complete note on solenoid and its magnetic field.
A solenoid is a long cylindrical coil consisting of many closely wound turns of insulated wire. When current passes through it, a magnetic field is produced. The field inside a long solenoid is approximately uniform.
The magnetic field is:
B = μ₀nI = μ₀NI/L
The field increases with current and turns per unit length. A suitable soft iron core makes the field much stronger and produces an electromagnet. The polarity can be determined using the right-hand grip rule.
B = μ₀nI = μ₀NI/L
The field increases with current and turns per unit length. A suitable soft iron core makes the field much stronger and produces an electromagnet. The polarity can be determined using the right-hand grip rule.
22. Assertion–Reason Questions
Assertion (A):
The magnetic field inside a long solenoid is approximately uniform.
Reason (R): The field lines inside a long solenoid are nearly parallel and equally spaced.
Reason (R): The field lines inside a long solenoid are nearly parallel and equally spaced.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A):
Increasing current in a solenoid increases its magnetic field.
Reason (R): B = μ₀nI.
Reason (R): B = μ₀nI.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A):
A soft iron core strengthens an electromagnet.
Reason (R): Soft iron can become strongly magnetised in the magnetic field produced by the coil.
Reason (R): Soft iron can become strongly magnetised in the magnetic field produced by the coil.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A):
Reversing current reverses the polarity of a solenoid.
Reason (R): The direction of the magnetic field depends on the direction of current.
Reason (R): The direction of the magnetic field depends on the direction of current.
Answer: Both A and R are true, and R correctly explains A.
23. HOTS Questions | उच्च स्तरीय प्रश्न
HOTS 1:
Two solenoids have the same current. Solenoid A has 1000 turns/m and Solenoid B has 2000 turns/m. Compare their magnetic fields.
B ∝ n
Therefore:
B₂/B₁ = 2000/1000 = 2.
Solenoid B produces twice the magnetic field.
HOTS 2:
A solenoid has 2000 turns in 1 m. Its length is increased to 2 m without changing total turns. What happens to B?
n = N/L.
When length doubles, n becomes half. Therefore B becomes half if current remains unchanged.
HOTS 3:
A solenoid's current is doubled while its turns per unit length are halved. What happens to B?
B ∝ nI.
The increase in I by factor 2 and decrease in n by factor 2 cancel each other.
Therefore B remains unchanged.
24. One-Minute Revision | एक मिनट Revision
🧲 Solenoid = Many Closely Wound Turns
Formula: B = μ₀nI
Since: n = N/L
Therefore: B = μ₀NI/L
Remember: Current ↑ → B ↑
Turns per unit length ↑ → B ↑
Soft iron core → Strong electromagnet
Current reversed → Polarity reversed
Inside long solenoid: Nearly uniform magnetic field.
Right-Hand Grip Rule: Fingers → Current
Thumb → North Pole
Formula: B = μ₀nI
Since: n = N/L
Therefore: B = μ₀NI/L
Remember: Current ↑ → B ↑
Turns per unit length ↑ → B ↑
Soft iron core → Strong electromagnet
Current reversed → Polarity reversed
Inside long solenoid: Nearly uniform magnetic field.
Right-Hand Grip Rule: Fingers → Current
Thumb → North Pole
25. Quick Concept Map
Electric Current
↓
Solenoid
↓
Magnetic Field
↓
B = μ₀nI
↓
Nearly Uniform Field
↓
Electromagnet
26. Exam Golden Points
✔ Solenoid = long coil of many closely wound turns.
✔ Current through solenoid produces magnetic field.
✔ Long solenoid has approximately uniform field inside.
✔ B = μ₀nI.
✔ n = N/L.
✔ Therefore B = μ₀NI/L.
✔ Increasing current increases B.
✔ Increasing turns per unit length increases B.
✔ Reversing current reverses polarity.
✔ Solenoid behaves like a bar magnet.
✔ Soft iron core makes an electromagnet stronger.
✔ Right-hand grip rule determines polarity.
✔ Current through solenoid produces magnetic field.
✔ Long solenoid has approximately uniform field inside.
✔ B = μ₀nI.
✔ n = N/L.
✔ Therefore B = μ₀NI/L.
✔ Increasing current increases B.
✔ Increasing turns per unit length increases B.
✔ Reversing current reverses polarity.
✔ Solenoid behaves like a bar magnet.
✔ Soft iron core makes an electromagnet stronger.
✔ Right-hand grip rule determines polarity.
27. Final Summary | अंतिम सारांश
English:
A solenoid is a long cylindrical coil containing many closely wound turns of insulated conducting wire. When current flows through it, a magnetic field is produced. The field inside a long solenoid is approximately uniform and strong. The magnetic field in an ideal long solenoid is:
हिन्दी:
सोलनॉइड एक लंबी बेलनाकार कुंडली है जिसमें विद्युतरोधी तार के बहुत सारे पास-पास लपेटे हुए फेरे होते हैं। इसमें धारा प्रवाहित करने पर चुंबकीय क्षेत्र उत्पन्न होता है। लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र लगभग एकसमान होता है। लंबे सोलनॉइड के लिए:
A solenoid is a long cylindrical coil containing many closely wound turns of insulated conducting wire. When current flows through it, a magnetic field is produced. The field inside a long solenoid is approximately uniform and strong. The magnetic field in an ideal long solenoid is:
B = μ₀nI
where n is the number of turns per unit length.
If the solenoid has N turns and length L:
B = μ₀NI/L
Increasing current or turns per unit length increases the field. A suitable soft iron core makes the field much stronger, forming an electromagnet. Reversing current reverses the polarity.
हिन्दी:
सोलनॉइड एक लंबी बेलनाकार कुंडली है जिसमें विद्युतरोधी तार के बहुत सारे पास-पास लपेटे हुए फेरे होते हैं। इसमें धारा प्रवाहित करने पर चुंबकीय क्षेत्र उत्पन्न होता है। लंबे सोलनॉइड के अंदर चुंबकीय क्षेत्र लगभग एकसमान होता है। लंबे सोलनॉइड के लिए:
B = μ₀nI
जहाँ n प्रति इकाई लंबाई फेरों की संख्या है।
यदि कुल फेरे N तथा लंबाई L हो:
B = μ₀NI/L
धारा तथा प्रति इकाई लंबाई फेरों की संख्या बढ़ाने पर चुंबकीय क्षेत्र बढ़ता है। नरम लोहे का कोर लगाने पर शक्तिशाली विद्युतचुंबक बनाया जा सकता है। धारा की दिशा बदलने पर ध्रुवता भी बदल जाती है।
Magnetic Effects of Electric Current
Solenoid and Its Magnetic Field
Class 10 Science | CBSE | Foundation | Competitive Preparation
Solenoid and Its Magnetic Field
Class 10 Science | CBSE | Foundation | Competitive Preparation
