🧲 Magnetic Effects of Electric Current
Important Definitions and Key Concepts | Class 10 Science | CBSE + Foundation + Competitive
🧲 Important Definitions and Key Concepts
1. Magnetic Field | चुंबकीय क्षेत्र
Magnetic Field:
The region around a magnet or a current-carrying conductor in which a magnetic force can be experienced is called a magnetic field.
हिंदी: चुंबक या विद्युत धारा प्रवाहित करने वाले चालक के चारों ओर का वह क्षेत्र जिसमें चुंबकीय बल का अनुभव किया जा सकता है, चुंबकीय क्षेत्र कहलाता है।
The region around a magnet or a current-carrying conductor in which a magnetic force can be experienced is called a magnetic field.
हिंदी: चुंबक या विद्युत धारा प्रवाहित करने वाले चालक के चारों ओर का वह क्षेत्र जिसमें चुंबकीय बल का अनुभव किया जा सकता है, चुंबकीय क्षेत्र कहलाता है।
Key Point: A current-carrying conductor produces a magnetic field around it.
मुख्य बिंदु: विद्युत धारा प्रवाहित करने वाला चालक अपने चारों ओर चुंबकीय क्षेत्र उत्पन्न करता है।
मुख्य बिंदु: विद्युत धारा प्रवाहित करने वाला चालक अपने चारों ओर चुंबकीय क्षेत्र उत्पन्न करता है।
2. Magnetic Field Lines | चुंबकीय क्षेत्र रेखाएँ
Magnetic Field Lines:
Imaginary lines used to represent the magnetic field are called magnetic field lines.
हिंदी: चुंबकीय क्षेत्र को दर्शाने वाली काल्पनिक रेखाओं को चुंबकीय क्षेत्र रेखाएँ कहते हैं।
Imaginary lines used to represent the magnetic field are called magnetic field lines.
हिंदी: चुंबकीय क्षेत्र को दर्शाने वाली काल्पनिक रेखाओं को चुंबकीय क्षेत्र रेखाएँ कहते हैं।
- The tangent at any point gives the direction of magnetic field.
- Closer lines indicate a stronger magnetic field.
- Magnetic field lines never intersect each other.
- They form closed continuous curves.
- Outside a bar magnet they travel from North to South.
- Inside the magnet they travel from South to North.
3. Uniform Magnetic Field | समरूप चुंबकीय क्षेत्र
A magnetic field having the same magnitude and direction at every point in a region is called a uniform magnetic field.
हिंदी: ऐसा चुंबकीय क्षेत्र जिसमें प्रत्येक बिंदु पर चुंबकीय क्षेत्र की परिमाण और दिशा समान हो, समरूप चुंबकीय क्षेत्र कहलाता है।
हिंदी: ऐसा चुंबकीय क्षेत्र जिसमें प्रत्येक बिंदु पर चुंबकीय क्षेत्र की परिमाण और दिशा समान हो, समरूप चुंबकीय क्षेत्र कहलाता है।
Representation: Uniform magnetic field is represented by parallel and equally spaced magnetic field lines.
प्रतिनिधित्व: समरूप चुंबकीय क्षेत्र को समान दूरी पर स्थित समानांतर रेखाओं द्वारा दर्शाया जाता है।
प्रतिनिधित्व: समरूप चुंबकीय क्षेत्र को समान दूरी पर स्थित समानांतर रेखाओं द्वारा दर्शाया जाता है।
4. Magnetic Field Due to Current | धारा के कारण चुंबकीय क्षेत्र
When electric current flows through a conductor, it produces a magnetic field around the conductor.
हिंदी: जब किसी चालक में विद्युत धारा प्रवाहित होती है, तो चालक के चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है।
हिंदी: जब किसी चालक में विद्युत धारा प्रवाहित होती है, तो चालक के चारों ओर चुंबकीय क्षेत्र उत्पन्न होता है।
For a long straight conductor: B = μ₀I / 2πr
| Symbol | Meaning |
|---|---|
| B | Magnetic field / चुंबकीय क्षेत्र |
| μ₀ | Permeability of free space / निर्वात की पारगम्यता |
| I | Current / विद्युत धारा |
| r | Distance from conductor / चालक से दूरी |
Important: B ∝ I and B ∝ 1/r.
Current बढ़ाने पर magnetic field बढ़ता है, जबकि conductor से दूरी बढ़ाने पर field घटता है।
Current बढ़ाने पर magnetic field बढ़ता है, जबकि conductor से दूरी बढ़ाने पर field घटता है।
5. Right-Hand Thumb Rule | दाहिने हाथ के अंगूठे का नियम
If a straight current-carrying conductor is held in the right hand with the thumb pointing in the direction of current, then the curled fingers indicate the direction of magnetic field lines.
हिंदी: यदि सीधे धारावाही चालक को दाहिने हाथ में इस प्रकार पकड़ा जाए कि अंगूठा धारा की दिशा में हो, तो मुड़ी हुई उंगलियाँ चुंबकीय क्षेत्र की दिशा बताती हैं।
हिंदी: यदि सीधे धारावाही चालक को दाहिने हाथ में इस प्रकार पकड़ा जाए कि अंगूठा धारा की दिशा में हो, तो मुड़ी हुई उंगलियाँ चुंबकीय क्षेत्र की दिशा बताती हैं।
Memory Trick: Thumb = Current, Curled Fingers = Magnetic Field.
याद रखें: अंगूठा = धारा, मुड़ी उंगलियाँ = चुंबकीय क्षेत्र।
याद रखें: अंगूठा = धारा, मुड़ी उंगलियाँ = चुंबकीय क्षेत्र।
6. Magnetic Field of a Circular Current-Carrying Loop
A circular current-carrying loop produces a magnetic field. At the centre of the loop, the field lines are approximately perpendicular to the plane of the loop.
हिंदी: वृत्ताकार धारावाही कुंडली अपने चारों ओर चुंबकीय क्षेत्र उत्पन्न करती है। कुंडली के केंद्र पर चुंबकीय क्षेत्र की दिशा कुंडली के तल के लंबवत होती है।
हिंदी: वृत्ताकार धारावाही कुंडली अपने चारों ओर चुंबकीय क्षेत्र उत्पन्न करती है। कुंडली के केंद्र पर चुंबकीय क्षेत्र की दिशा कुंडली के तल के लंबवत होती है।
The magnetic field becomes stronger when:
- Current is increased.
- Number of turns is increased.
- Distance from the effective source is reduced.
7. Solenoid | परिनालिका
A solenoid is a long cylindrical coil consisting of many closely wound turns of insulated wire.
हिंदी: कुंडलित विद्युतरोधी तार की बहुत सारी पास-पास स्थित फेरों वाली लंबी बेलनाकार कुंडली को परिनालिका (Solenoid) कहते हैं।
हिंदी: कुंडलित विद्युतरोधी तार की बहुत सारी पास-पास स्थित फेरों वाली लंबी बेलनाकार कुंडली को परिनालिका (Solenoid) कहते हैं।
Important Properties:
- Magnetic field inside a long solenoid is approximately uniform.
- It behaves like a bar magnet.
- Increasing current increases magnetic field strength.
- Increasing number of turns increases field strength.
- A soft iron core can make an electromagnet stronger.
8. Electromagnet | विद्युत चुंबक
An electromagnet is a temporary magnet produced by passing electric current through a coil, usually wound around a soft iron core.
हिंदी: विद्युत धारा प्रवाहित करके बनाया गया अस्थायी चुंबक, जिसमें सामान्यतः नरम लोहे की क्रोड का उपयोग किया जाता है, विद्युत चुंबक कहलाता है।
हिंदी: विद्युत धारा प्रवाहित करके बनाया गया अस्थायी चुंबक, जिसमें सामान्यतः नरम लोहे की क्रोड का उपयोग किया जाता है, विद्युत चुंबक कहलाता है।
| Factor | Effect on Strength |
|---|---|
| Current ↑ | Magnetic strength ↑ |
| Number of turns ↑ | Magnetic strength ↑ |
| Soft iron core | Magnetic strength greatly increases |
9. Force on a Current-Carrying Conductor
A current-carrying conductor placed in a magnetic field experiences a force.
हिंदी: चुंबकीय क्षेत्र में रखे धारावाही चालक पर चुंबकीय बल कार्य करता है।
हिंदी: चुंबकीय क्षेत्र में रखे धारावाही चालक पर चुंबकीय बल कार्य करता है।
F = BIL sin θ
| Quantity | Meaning |
|---|---|
| F | Force in newton (N) |
| B | Magnetic field in tesla (T) |
| I | Current in ampere (A) |
| L | Length of conductor in metre (m) |
| θ | Angle between current direction and magnetic field |
Maximum force: θ = 90°
Zero force: θ = 0° or 180°
Zero force: θ = 0° or 180°
10. Fleming's Left-Hand Rule
Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of magnetic field and the middle finger in the direction of current, the thumb gives the direction of force or motion.
हिंदी: बाएँ हाथ के अंगूठे, तर्जनी और मध्यमा को परस्पर लंबवत रखें। तर्जनी चुंबकीय क्षेत्र, मध्यमा धारा और अंगूठा बल/गति की दिशा बताता है।
हिंदी: बाएँ हाथ के अंगूठे, तर्जनी और मध्यमा को परस्पर लंबवत रखें। तर्जनी चुंबकीय क्षेत्र, मध्यमा धारा और अंगूठा बल/गति की दिशा बताता है।
| Finger | Represents |
|---|---|
| Forefinger | Magnetic Field (B) |
| Middle finger | Current (I) |
| Thumb | Force / Motion (F) |
11. Electric Motor | विद्युत मोटर
An electric motor is a device that converts electrical energy into mechanical energy.
हिंदी: विद्युत मोटर वह यंत्र है जो विद्युत ऊर्जा को यांत्रिक ऊर्जा में बदलता है।
हिंदी: विद्युत मोटर वह यंत्र है जो विद्युत ऊर्जा को यांत्रिक ऊर्जा में बदलता है।
Principle: A current-carrying coil placed in a magnetic field experiences a force and rotates.
मुख्य भाग: Armature/coil, permanent magnet, split-ring commutator, brushes and battery.
मुख्य भाग: Armature/coil, permanent magnet, split-ring commutator, brushes and battery.
12. Electromagnetic Induction | विद्युत चुंबकीय प्रेरण
The phenomenon of production of induced current in a coil due to a change in magnetic field or magnetic flux linked with the coil is called electromagnetic induction.
हिंदी: कुंडली से संबद्ध चुंबकीय फ्लक्स में परिवर्तन के कारण कुंडली में प्रेरित विद्युत धारा उत्पन्न होने की घटना को विद्युत चुंबकीय प्रेरण कहते हैं।
हिंदी: कुंडली से संबद्ध चुंबकीय फ्लक्स में परिवर्तन के कारण कुंडली में प्रेरित विद्युत धारा उत्पन्न होने की घटना को विद्युत चुंबकीय प्रेरण कहते हैं।
Key Idea: Changing magnetic field → induced current.
मुख्य विचार: चुंबकीय क्षेत्र में परिवर्तन → प्रेरित धारा।
मुख्य विचार: चुंबकीय क्षेत्र में परिवर्तन → प्रेरित धारा।
13. Fleming's Right-Hand Rule
Stretch the thumb, forefinger and middle finger of the right hand mutually perpendicular to each other. If the forefinger points in the direction of magnetic field and the thumb in the direction of motion of the conductor, the middle finger gives the direction of induced current.
हिंदी: दाएँ हाथ के अंगूठे, तर्जनी और मध्यमा को परस्पर लंबवत रखें। तर्जनी चुंबकीय क्षेत्र, अंगूठा चालक की गति और मध्यमा प्रेरित धारा की दिशा बताता है।
हिंदी: दाएँ हाथ के अंगूठे, तर्जनी और मध्यमा को परस्पर लंबवत रखें। तर्जनी चुंबकीय क्षेत्र, अंगूठा चालक की गति और मध्यमा प्रेरित धारा की दिशा बताता है।
| Finger | Represents |
|---|---|
| Thumb | Motion of conductor |
| Forefinger | Magnetic field |
| Middle finger | Induced current |
14. Electric Generator | विद्युत जनित्र
An electric generator is a device that converts mechanical energy into electrical energy using electromagnetic induction.
हिंदी: विद्युत जनित्र विद्युत चुंबकीय प्रेरण के सिद्धांत पर यांत्रिक ऊर्जा को विद्युत ऊर्जा में परिवर्तित करता है।
हिंदी: विद्युत जनित्र विद्युत चुंबकीय प्रेरण के सिद्धांत पर यांत्रिक ऊर्जा को विद्युत ऊर्जा में परिवर्तित करता है।
AC Generator: Uses slip rings.
DC Generator: Uses a split-ring commutator.
DC Generator: Uses a split-ring commutator.
15. AC and DC | प्रत्यावर्ती और दिष्ट धारा
| AC | DC |
|---|---|
| Direction changes periodically. | Flows in one direction. |
| Produced by AC generators and supplied through mains. | Obtained from cells, batteries and DC sources. |
| Used for domestic power supply. | Used in batteries and many electronic circuits. |
16. Live, Neutral and Earth Wires
| Wire | Basic Function |
|---|---|
| Live Wire | Carries potential difference from supply to appliance. |
| Neutral Wire | Provides the return path in the normal circuit. |
| Earth Wire | Provides a low-resistance path for fault current and helps reduce electric shock risk. |
Safety: Fuse/MCB protection is normally connected in the live side of a domestic circuit so that the appliance is disconnected from the supply when protection operates.
17. Fuse | फ्यूज
A fuse is a safety device containing a thin wire that melts when excessive current flows through it and breaks the circuit.
हिंदी: फ्यूज एक सुरक्षा उपकरण है जिसमें पतला तार होता है। अत्यधिक धारा बहने पर तार गर्म होकर पिघल जाता है और परिपथ को तोड़ देता है।
हिंदी: फ्यूज एक सुरक्षा उपकरण है जिसमें पतला तार होता है। अत्यधिक धारा बहने पर तार गर्म होकर पिघल जाता है और परिपथ को तोड़ देता है।
H = I²Rt
Never replace a fuse with a thick ordinary copper wire.
फ्यूज के स्थान पर मोटे सामान्य तांबे के तार का उपयोग नहीं करना चाहिए।
फ्यूज के स्थान पर मोटे सामान्य तांबे के तार का उपयोग नहीं करना चाहिए।
18. Earthing | अर्थिंग
Earthing is the process of connecting the metallic body of an electrical appliance to the earth through a low-resistance conducting path.
हिंदी: विद्युत उपकरण के धात्विक शरीर को कम प्रतिरोध वाले चालक द्वारा पृथ्वी से जोड़ने की प्रक्रिया को अर्थिंग कहते हैं।
हिंदी: विद्युत उपकरण के धात्विक शरीर को कम प्रतिरोध वाले चालक द्वारा पृथ्वी से जोड़ने की प्रक्रिया को अर्थिंग कहते हैं।
Purpose:
- Provides a safe path for leakage/fault current.
- Helps protect a person from electric shock.
- Is especially important for appliances with metallic bodies.
19. Overloading | अतिभारण
Overloading occurs when too many appliances are connected to a circuit or the total current exceeds the safe capacity of the circuit.
हिंदी: जब किसी परिपथ में उसकी सुरक्षित क्षमता से अधिक विद्युत धारा प्रवाहित होने लगे, तो उसे अतिभारण कहते हैं।
हिंदी: जब किसी परिपथ में उसकी सुरक्षित क्षमता से अधिक विद्युत धारा प्रवाहित होने लगे, तो उसे अतिभारण कहते हैं।
20. Short Circuit | लघु परिपथ
A short circuit occurs when live and neutral wires come into direct or very low-resistance contact, causing a very large current to flow.
हिंदी: जब लाइव और न्यूट्रल तार सीधे या बहुत कम प्रतिरोध वाले संपर्क में आ जाते हैं और बहुत अधिक धारा प्रवाहित होती है, तो इसे शॉर्ट सर्किट कहते हैं।
हिंदी: जब लाइव और न्यूट्रल तार सीधे या बहुत कम प्रतिरोध वाले संपर्क में आ जाते हैं और बहुत अधिक धारा प्रवाहित होती है, तो इसे शॉर्ट सर्किट कहते हैं।
21. Magnetic Field and Its SI Unit
The SI unit of magnetic field is tesla (T).
हिंदी: चुंबकीय क्षेत्र की SI इकाई टेस्ला (T) है।
हिंदी: चुंबकीय क्षेत्र की SI इकाई टेस्ला (T) है।
22. Electromagnet vs Permanent Magnet
| Electromagnet | Permanent Magnet |
|---|---|
| Works mainly when current flows. | Retains magnetism without continuous current. |
| Can be switched ON/OFF. | Cannot normally be switched ON/OFF. |
| Strength can be varied. | Strength is comparatively fixed. |
| Often uses soft iron core. | Uses suitable permanent magnetic materials. |
23. Important Symbols and Memory Rules
⊙ Current Out of Page
⊗ Current Into Page
N → S Outside Magnet
S → N Inside Magnet
| Rule / Formula | Remember |
|---|---|
| Right-Hand Thumb Rule | Thumb = Current, Fingers = Magnetic Field |
| Fleming Left-Hand Rule | Field – Current – Force |
| Fleming Right-Hand Rule | Field – Motion – Induced Current |
| Motor | Electrical → Mechanical |
| Generator | Mechanical → Electrical |
| Electromagnetic Induction | Changing magnetic flux → induced current |
24. Important Formula Sheet
| Formula | Use |
|---|---|
| B = μ₀I / 2πr | Magnetic field due to long straight conductor |
| F = BIL sin θ | Force on current-carrying conductor |
| H = I²Rt | Heating effect of current |
| P = VI | Electrical power |
| P = I²R | Power relation |
| P = V²/R | Power relation |
| E = Pt | Electrical energy |
25. 30 MCQs | Multiple Choice Questions
1. The region around a magnet where magnetic force can be detected is called:
A. Electric field
B. Magnetic field
C. Gravitational field
D. Electric potential
Answer: B — It is called magnetic field.
2. Magnetic field lines outside a bar magnet move from:
A. South to North
B. East to West
C. North to South
D. West to East
Answer: C
3. Magnetic field lines never:
A. Intersect each other
B. Form curves
C. Exist around magnets
D. Show direction
Answer: A
4. The SI unit of magnetic field is:
A. Newton
B. Ampere
C. Volt
D. Tesla
Answer: D
5. Around a straight current-carrying conductor, magnetic field lines are:
A. Concentric circles
B. Straight parallel lines
C. Ellipses only
D. Random lines
Answer: A
6. Direction of magnetic field around a straight conductor is found by:
A. Ohm's law
B. Fleming's left-hand rule
C. Right-hand thumb rule
D. Joule's law
Answer: C
7. In the right-hand thumb rule, the thumb represents:
A. Magnetic field
B. Current
C. Force
D. Resistance
Answer: B
8. In the right-hand thumb rule, curled fingers represent:
A. Current
B. Force
C. Magnetic field
D. Voltage
Answer: C
9. A solenoid consists of:
A. A single straight wire
B. Many closely wound turns of wire
C. Only a battery
D. A fuse wire
Answer: B
10. The magnetic field inside a long solenoid is approximately:
A. Uniform
B. Zero
C. Random
D. Circular only
Answer: A
11. An electromagnet generally uses which core?
A. Copper
B. Aluminium
C. Soft iron
D. Plastic
Answer: C
12. Force on a current-carrying conductor is maximum when θ is:
A. 0°
B. 45°
C. 180°
D. 90°
Answer: D
13. The formula for force on a current-carrying conductor is:
A. F = BIL sin θ
B. F = IR
C. F = V/R
D. F = Pt
Answer: A
14. Fleming's left-hand rule gives the direction of:
A. Resistance
B. Force
C. Voltage
D. Resistance change
Answer: B
15. In Fleming's left-hand rule, the middle finger represents:
A. Current
B. Force
C. Magnetic field
D. Motion
Answer: A
16. An electric motor converts:
A. Mechanical energy into electrical energy
B. Heat into electrical energy
C. Electrical energy into mechanical energy
D. Chemical energy into light only
Answer: C
17. The principle of an electric motor is based on:
A. Heating effect
B. Force on a current-carrying conductor in magnetic field
C. Chemical effect
D. Electrolysis
Answer: B
18. Electromagnetic induction was discovered by:
A. Newton
B. Faraday
C. Ohm
D. Joule
Answer: B
19. Electromagnetic induction involves production of:
A. Resistance
B. Heat only
C. Induced current due to changing magnetic flux
D. Static charge only
Answer: C
20. Fleming's right-hand rule is used to determine:
A. Direction of induced current
B. Resistance
C. Electric power
D. Heat
Answer: A
21. An electric generator converts:
A. Electrical energy into mechanical energy
B. Mechanical energy into electrical energy
C. Heat into sound
D. Light into heat
Answer: B
22. AC generator normally uses:
A. Slip rings
B. Fuse
C. Capacitor
D. Transformer core only
Answer: A
23. A fuse protects a circuit from:
A. Low voltage only
B. Excessive current
C. Low resistance only
D. Normal current
Answer: B
24. Fuse works mainly due to:
A. Magnetic effect only
B. Chemical effect
C. Heating effect of current
D. Photoelectric effect
Answer: C
25. The earth wire is mainly used for:
A. Increasing voltage
B. Reducing resistance of appliance
C. Providing a safe path for fault current
D. Increasing current in normal operation
Answer: C
26. Which wire normally carries the supply potential to an appliance?
A. Earth
B. Neutral
C. Live
D. Shield
Answer: C
27. A short circuit generally causes:
A. Very large current
B. Zero current always
C. No heating
D. Higher resistance
Answer: A
28. The SI unit of force is:
A. Tesla
B. Newton
C. Ampere
D. Volt
Answer: B
29. The relation P = VI represents:
A. Electrical power
B. Resistance
C. Charge
D. Magnetic flux
Answer: A
30. Which device converts mechanical energy into electrical energy?
A. Motor
B. Fuse
C. Generator
D. MCB
Answer: C
26. 30 Subjective Questions with Answers
2 Marks
Q1. What is a magnetic field?
A magnetic field is the region around a magnet or current-carrying conductor where magnetic force can be experienced.
हिंदी: चुंबक या धारावाही चालक के आसपास का वह क्षेत्र जिसमें चुंबकीय बल अनुभव किया जा सकता है, चुंबकीय क्षेत्र कहलाता है।
हिंदी: चुंबक या धारावाही चालक के आसपास का वह क्षेत्र जिसमें चुंबकीय बल अनुभव किया जा सकता है, चुंबकीय क्षेत्र कहलाता है।
2 Marks
Q2. What are magnetic field lines?
They are imaginary lines used to represent the direction and relative strength of a magnetic field.
2 Marks
Q3. Write two properties of magnetic field lines.
1. They never intersect each other.
2. Their closeness indicates the strength of the magnetic field.
2. Their closeness indicates the strength of the magnetic field.
2 Marks
Q4. State the right-hand thumb rule.
Thumb gives current direction and curled fingers give magnetic field direction around a straight conductor.
2 Marks
Q5. Define solenoid.
A solenoid is a long cylindrical coil consisting of many closely wound turns of insulated wire.
2 Marks
Q6. What is an electromagnet?
An electromagnet is a temporary magnet produced by passing current through a coil, usually around a soft iron core.
2 Marks
Q7. What is electromagnetic induction?
It is the phenomenon of production of induced current due to a change in magnetic flux linked with a conductor or coil.
2 Marks
Q8. State Fleming's left-hand rule.
Forefinger indicates magnetic field, middle finger indicates current and thumb indicates force or motion.
2 Marks
Q9. State Fleming's right-hand rule.
Forefinger indicates magnetic field, thumb indicates conductor motion and middle finger indicates induced current.
3 Marks
Q10. What factors affect the force on a current-carrying conductor?
The force depends on:
1. Magnetic field strength B.
2. Current I.
3. Length L of conductor.
4. Angle θ between current and magnetic field.
F = BIL sinθ.
1. Magnetic field strength B.
2. Current I.
3. Length L of conductor.
4. Angle θ between current and magnetic field.
F = BIL sinθ.
3 Marks
Q11. Explain why magnetic field around a straight conductor consists of circular lines.
The magnetic field produced by a straight current-carrying conductor is symmetrical around the conductor. At equal distances from the conductor, the field has equal magnitude, so the field lines form concentric circles around the conductor.
3 Marks
Q12. How can the strength of an electromagnet be increased?
Increase the current, increase the number of turns of the coil and use a suitable soft iron core.
3 Marks
Q13. Give three differences between motor and generator.
Motor converts electrical energy into mechanical energy, whereas generator converts mechanical energy into electrical energy. Motor works on force on a current-carrying conductor; generator works on electromagnetic induction. Their energy input-output directions are opposite.
3 Marks
Q14. Why does a current-carrying conductor experience force in a magnetic field?
The magnetic field produced by the current interacts with the external magnetic field. This interaction produces a force on the conductor.
3 Marks
Q15. What is the role of a split-ring commutator in an electric motor?
It reverses the direction of current in the coil after every half rotation, helping the coil continue rotating in the same mechanical direction.
4 Marks
Q16. Explain the principle and working of an electric motor.
An electric motor works on the principle that a current-carrying coil placed in a magnetic field experiences a force. The two sides of the coil experience forces in opposite directions, producing rotation. The split-ring commutator reverses the current after every half turn, maintaining the rotation. Thus electrical energy is converted into mechanical energy.
4 Marks
Q17. Explain electromagnetic induction.
When a magnet is moved towards or away from a coil, the magnetic flux linked with the coil changes. This change produces an induced current in the coil. Reversing the motion reverses the induced current. Faster change generally produces a larger induced effect.
4 Marks
Q18. Explain the construction of an electric generator.
A basic generator consists of a rotating coil placed in a magnetic field, an axle, brushes and rings for collecting current. In an AC generator, slip rings are used. Mechanical rotation of the coil changes magnetic flux and induces current.
4 Marks
Q19. Differentiate between AC and DC.
AC changes direction periodically, whereas DC flows in one direction. AC is commonly supplied through domestic mains, while DC is commonly obtained from cells and batteries. AC is suitable for efficient long-distance transmission with transformers, while many electronic systems use DC internally.
4 Marks
Q20. Explain the purpose of earthing.
Earthing connects the metallic body of an appliance to earth through a low-resistance path. If insulation fails and the body becomes live, fault current can flow safely through the earth path, helping protective devices operate and reducing shock risk.
5 Marks
Q21. Explain the right-hand thumb rule with an example.
Hold a straight current-carrying conductor in the right hand. Point the thumb in the direction of conventional current. The curled fingers show the direction of magnetic field lines. If current is upward, the magnetic field circles around the conductor according to the curled fingers. Reversing current reverses the field direction.
5 Marks
Q22. Explain the magnetic field due to a solenoid.
A solenoid consists of many closely wound turns of insulated wire. When current flows, each turn produces a magnetic field and the fields combine. Inside a long solenoid the field is approximately uniform. The solenoid behaves like a bar magnet. Increasing current or number of turns increases field strength. A soft iron core further strengthens the field.
5 Marks
Q23. Explain Fleming's left-hand rule.
Stretch the thumb, forefinger and middle finger of the left hand mutually perpendicular. The forefinger points in the direction of magnetic field, the middle finger in the direction of current, and the thumb gives the direction of force or motion.
5 Marks
Q24. Explain Fleming's right-hand rule.
Stretch the thumb, forefinger and middle finger of the right hand mutually perpendicular. The forefinger represents magnetic field, thumb represents motion of the conductor and middle finger represents induced current.
6 Marks
Q25. Explain the important concepts of magnetic effects of electric current.
Important concepts include magnetic field around a current-carrying conductor, right-hand thumb rule, magnetic field of a circular loop, solenoid, electromagnet, force on a current-carrying conductor, Fleming's left-hand rule, electric motor, electromagnetic induction, Fleming's right-hand rule and electric generator.
6 Marks
Q26. Compare electric motor and electric generator.
| Motor | Generator |
|---|---|
| Electrical energy → Mechanical energy | Mechanical energy → Electrical energy |
| Works on force on current-carrying conductor | Works on electromagnetic induction |
| Uses split-ring commutator in a DC motor | AC generator uses slip rings |
6 Marks
Q27. Explain domestic electrical safety using live, neutral, earth, fuse and MCB.
The live wire carries supply potential to appliances and the neutral provides the normal return path. The earth wire connects exposed metallic parts to earth through a low-resistance path. A fuse melts when excessive current flows, while an MCB trips and interrupts the circuit during abnormal current conditions. These arrangements help reduce fire and shock risks when correctly installed and maintained.
6 Marks
Q28. Derive the relation for force on a current-carrying conductor.
For a conductor of length L carrying current I in a magnetic field B at angle θ, the magnetic force is:
F = BIL sinθ
Hence force is directly proportional to B, I and L for a fixed angle. It is maximum at 90° and zero when the conductor is parallel or antiparallel to the magnetic field.
F = BIL sinθ
Hence force is directly proportional to B, I and L for a fixed angle. It is maximum at 90° and zero when the conductor is parallel or antiparallel to the magnetic field.
6 Marks
Q29. Explain electromagnetic induction and the working principle of a generator.
Electromagnetic induction is the production of induced current when magnetic flux linked with a conductor changes. In a generator, a coil rotates in a magnetic field, continuously changing the magnetic flux through it. An induced current is produced and collected through rings and brushes. Thus mechanical energy is converted into electrical energy.
6 Marks
Q30. Prepare a complete one-page revision note for this chapter.
Magnetic field is the region where magnetic force acts. Current produces magnetic field. Right-hand thumb rule gives field direction. A solenoid produces an approximately uniform field inside. An electromagnet is a temporary magnet. A current-carrying conductor in a magnetic field experiences force, F=BILsinθ. Fleming's left-hand rule gives force direction. Motor converts electrical to mechanical energy. Electromagnetic induction produces current due to changing magnetic flux. Fleming's right-hand rule gives induced-current direction. Generator converts mechanical to electrical energy. Fuse, MCB, earthing, live, neutral and earth wires are important for domestic electrical safety.
27. Assertion–Reason Questions
Assertion (A): Magnetic field lines never intersect each other.
Reason (R): At any point, magnetic field has a unique direction.
Reason (R): At any point, magnetic field has a unique direction.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): A current-carrying conductor produces a magnetic field.
Reason (R): Moving electric charges can produce magnetic effects.
Reason (R): Moving electric charges can produce magnetic effects.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): The force on a conductor is maximum when it is perpendicular to the magnetic field.
Reason (R): In F=BILsinθ, sin90°=1.
Reason (R): In F=BILsinθ, sin90°=1.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): An electric motor converts electrical energy into mechanical energy.
Reason (R): A current-carrying conductor in a magnetic field experiences force.
Reason (R): A current-carrying conductor in a magnetic field experiences force.
Answer: Both A and R are true, and R correctly explains A.
Assertion (A): A generator works on electromagnetic induction.
Reason (R): Changing magnetic flux can induce current in a conductor.
Reason (R): Changing magnetic flux can induce current in a conductor.
Answer: Both A and R are true, and R correctly explains A.
28. HOTS | Higher Order Thinking Questions
HOTS 1: If the current in a straight conductor is doubled, what happens to the magnetic field at the same distance?
Since B ∝ I, the magnetic field becomes twice its original value.
HOTS 2: If the distance from a straight current-carrying conductor is doubled, what happens to B?
Since B ∝ 1/r, the magnetic field becomes half its original value.
HOTS 3: What happens to the direction of magnetic field if the current direction is reversed?
The direction of magnetic field is also reversed.
HOTS 4: Why is soft iron suitable for an electromagnet?
Soft iron is easily magnetised and demagnetised, making it suitable for a temporary magnet.
HOTS 5: Why does an electric motor continue rotating after the coil completes half a turn?
The split-ring commutator reverses the current through the coil after each half turn, so the torque continues to act in the same rotational direction.
29. Important Numerical Practice
Numerical 1: A conductor of length 0.5 m carries 4 A current in a 0.2 T magnetic field at 90°. Find the force.
F = BIL sinθ
= 0.2 × 4 × 0.5 × 1
= 0.4 N
= 0.2 × 4 × 0.5 × 1
= 0.4 N
Numerical 2: A conductor carries 5 A current in a magnetic field of 0.3 T. Its length is 2 m and it is perpendicular to the field. Find force.
F = 0.3 × 5 × 2 × 1
= 3 N
= 3 N
Numerical 3: What happens to magnetic field if current changes from 2 A to 6 A at the same distance?
B ∝ I.
6/2 = 3.
Therefore magnetic field becomes 3 times.
6/2 = 3.
Therefore magnetic field becomes 3 times.
Numerical 4: Calculate power of a 230 V appliance drawing 2 A current.
P = VI
= 230 × 2
= 460 W
= 230 × 2
= 460 W
30. Golden Points | परीक्षा के लिए सबसे महत्वपूर्ण
✔ Current-carrying conductor produces magnetic field.
✔ Magnetic field lines never intersect.
✔ Closer field lines indicate stronger field.
✔ Right-hand thumb rule gives magnetic field direction.
✔ Solenoid behaves like a bar magnet.
✔ Soft iron is commonly used in electromagnets.
✔ F = BIL sinθ.
✔ Maximum force occurs at 90°.
✔ Fleming's left-hand rule gives force direction.
✔ Motor converts electrical energy into mechanical energy.
✔ Electromagnetic induction produces induced current due to changing magnetic flux.
✔ Fleming's right-hand rule gives induced current direction.
✔ Generator converts mechanical energy into electrical energy.
✔ Fuse protects against excessive current.
✔ Earthing reduces electric shock risk by providing a low-resistance fault-current path.
✔ Magnetic field lines never intersect.
✔ Closer field lines indicate stronger field.
✔ Right-hand thumb rule gives magnetic field direction.
✔ Solenoid behaves like a bar magnet.
✔ Soft iron is commonly used in electromagnets.
✔ F = BIL sinθ.
✔ Maximum force occurs at 90°.
✔ Fleming's left-hand rule gives force direction.
✔ Motor converts electrical energy into mechanical energy.
✔ Electromagnetic induction produces induced current due to changing magnetic flux.
✔ Fleming's right-hand rule gives induced current direction.
✔ Generator converts mechanical energy into electrical energy.
✔ Fuse protects against excessive current.
✔ Earthing reduces electric shock risk by providing a low-resistance fault-current path.
31. One-Minute Revision
Magnetic Field → Region where magnetic force acts.
Current → Produces magnetic field.
Right-Hand Thumb Rule → Current → Magnetic field direction.
Solenoid → Many turns → Strong, approximately uniform internal field.
Electromagnet → Temporary magnet produced by current.
F = BIL sinθ → Force on conductor.
Left-Hand Rule → Force direction.
Motor → Electrical → Mechanical.
Electromagnetic Induction → Changing magnetic flux → Induced current.
Right-Hand Rule → Induced current direction.
Generator → Mechanical → Electrical.
Fuse + MCB + Earthing → Electrical safety.
Current → Produces magnetic field.
Right-Hand Thumb Rule → Current → Magnetic field direction.
Solenoid → Many turns → Strong, approximately uniform internal field.
Electromagnet → Temporary magnet produced by current.
F = BIL sinθ → Force on conductor.
Left-Hand Rule → Force direction.
Motor → Electrical → Mechanical.
Electromagnetic Induction → Changing magnetic flux → Induced current.
Right-Hand Rule → Induced current direction.
Generator → Mechanical → Electrical.
Fuse + MCB + Earthing → Electrical safety.
32. Concept Map
33. Final Summary
The magnetic effect of electric current is one of the most important concepts of Class 10 Science. Electric current produces a magnetic field around a conductor. The direction of this field can be determined using the right-hand thumb rule. A solenoid can produce a strong, approximately uniform magnetic field and can be used to make an electromagnet.
A current-carrying conductor placed in a magnetic field experiences force according to F = BIL sinθ. Fleming's left-hand rule determines the direction of this force, forming the basic principle of an electric motor.
A changing magnetic flux can produce an induced current. This phenomenon is called electromagnetic induction. Fleming's right-hand rule determines the direction of induced current, and the principle is used in electric generators.
For domestic electrical safety, live, neutral and earth wires, fuse, MCB and earthing are important concepts. Understanding these definitions, rules, formulas and applications is essential for CBSE Board, Foundation and competitive examinations.
🧲 Class 10 Science | Magnetic Effects of Electric Current
Important Definitions • Rules • Formulae • Concepts • MCQs • Subjective Questions • HOTS • Revision
CBSE + Foundation + Competitive Preparation
Important Definitions • Rules • Formulae • Concepts • MCQs • Subjective Questions • HOTS • Revision
CBSE + Foundation + Competitive Preparation
