Magnetic Effects of Electric Current
1. Magnetic Field
A magnetic field is the region around a magnet or a current-carrying conductor where its magnetic effect can be felt.
Magnetic Field Lines
- Imaginary lines used to represent magnetic field.
- Outside the magnet, they go from North Pole to South Pole.
- Inside the magnet, they go from South Pole to North Pole.
Properties
- Magnetic field lines never intersect.
- Closer the lines, stronger the magnetic field.
- Parallel and equally spaced lines show uniform magnetic field.
2. Magnetic Field Due to a Current-Carrying Conductor
(a) Straight Current-Carrying Conductor
- Produces circular magnetic field lines around it.
- Direction is given by Right-Hand Thumb Rule.
Right-Hand Thumb Rule
- Thumb → Direction of current
- Curled fingers → Direction of magnetic field
(b) Circular Loop Carrying Current
- Magnetic field is stronger at the center of the loop.
- Field lines are circular near the wire.
(c) Solenoid
A solenoid is a long coil of insulated copper wire.
- Produces magnetic field similar to a bar magnet.
- Inside solenoid, magnetic field is strong and uniform.
Uses: Electric bell, electromagnets
3. Electromagnet
An electromagnet is a temporary magnet produced by passing electric current through a solenoid.
Factors Increasing Strength
- Increase in current
- Increase in number of turns
- Using soft iron core
4. Fleming’s Left-Hand Rule
Used to find the direction of force on a current-carrying conductor placed in a magnetic field.
- Forefinger → Magnetic field
- Middle finger → Current
- Thumb → Direction of force (motion)
5. Force on a Current-Carrying Conductor
When a conductor carrying current is placed in a magnetic field, it experiences a force.
Factors Affecting Force
- Strength of magnetic field
- Magnitude of current
- Length of conductor
6. Electric Motor
An electric motor converts electrical energy into mechanical energy.
Principle
Based on the force experienced by a current-carrying conductor in a magnetic field.
Main Parts
- Armature (coil)
- Split ring commutator
- Carbon brushes
- Magnet
Uses: Fans, mixers, washing machines
7. Electromagnetic Induction
The phenomenon of producing electric current by changing magnetic field around a conductor.
Discovered by Michael Faraday.
8. Fleming’s Right-Hand Rule
Used to find the direction of induced current.
- Thumb → Direction of motion of conductor
- Forefinger → Magnetic field
- Middle finger → Induced current
9. Electric Generator
An electric generator converts mechanical energy into electrical energy.
Types
- AC Generator
- DC Generator
Principle
Based on electromagnetic induction.
10. Alternating Current (AC) and Direct Current (DC)
AC (Alternating Current)
- Changes direction periodically
- Used in homes
DC (Direct Current)
- Flows in one direction
- Supplied by cells and batteries
11. Domestic Electric Circuits
- Live wire – Red/Brown
- Neutral wire – Black/Blue
- Earth wire – Green
Electric Fuse
- Safety device
- Made of thin wire with low melting point
- Protects from overloading and short circuit
12. Short Circuit and Overloading
Short Circuit
Occurs when live and neutral wires come in direct contact.
Overloading
Occurs when too many appliances are connected to a single circuit.
Important for Exams
- Fleming’s Left Hand Rule → Motor
- Fleming’s Right Hand Rule → Generator
- Electric Motor Diagram
- AC vs DC Differences
- Reason for fuse melting
MCQs: Magnetic Effects of Electric Current
1. The region around a magnet where its effect can be felt is called:
a) Electric field
b) Magnetic field
c) Gravitational field
d) Force field
Answer: b) Magnetic field
2. Magnetic field lines outside a bar magnet emerge from:
a) South pole
b) Both poles
c) North pole
d) Centre
Answer: c) North pole
3. Which rule is used to determine the direction of magnetic field around a current-carrying conductor?
a) Fleming’s Left Hand Rule
b) Fleming’s Right Hand Rule
c) Right-Hand Thumb Rule
d) Maxwell’s Rule
Answer: c) Right-Hand Thumb Rule
4. The magnetic field at the centre of a circular current-carrying loop is:
a) Zero
b) Weak
c) Strongest
d) Random
Answer: c) Strongest
5. A solenoid produces a magnetic field similar to that of:
a) A straight wire
b) A circular loop
c) A bar magnet
d) Earth
Answer: c) A bar magnet
6. Which material is commonly used as the core of an electromagnet?
a) Steel
b) Copper
c) Soft iron
d) Aluminium
Answer: c) Soft iron
7. Which of the following increases the strength of an electromagnet?
a) Decreasing current
b) Using aluminium core
c) Increasing number of turns
d) Reducing turns
Answer: c) Increasing number of turns
8. Fleming’s Left-Hand Rule is used in:
a) Electric generator
b) Electric motor
c) Transformer
d) Battery
Answer: b) Electric motor
9. The direction of force on a current-carrying conductor is given by:
a) Right-Hand Thumb Rule
b) Fleming’s Left Hand Rule
c) Fleming’s Right Hand Rule
d) Coulomb’s Law
Answer: b) Fleming’s Left Hand Rule
10. An electric motor converts:
a) Mechanical energy into electrical energy
b) Electrical energy into mechanical energy
c) Chemical energy into heat
d) Heat into electrical energy
Answer: b) Electrical energy into mechanical energy
11. Which part of an electric motor reverses the direction of current?
a) Armature
b) Carbon brushes
c) Split ring commutator
d) Magnet
Answer: c) Split ring commutator
12. The phenomenon of producing electric current due to changing magnetic field is called:
a) Electric conduction
b) Magnetisation
c) Electromagnetic induction
d) Electrolysis
Answer: c) Electromagnetic induction
13. Electromagnetic induction was discovered by:
a) Newton
b) Maxwell
c) Faraday
d) Tesla
Answer: c) Faraday
14. Fleming’s Right-Hand Rule is used in:
a) Electric motor
b) Electromagnet
c) Electric generator
d) Electric fuse
Answer: c) Electric generator
15. An electric generator converts:
a) Electrical energy into mechanical energy
b) Mechanical energy into electrical energy
c) Heat energy into electrical energy
d) Chemical energy into electrical energy
Answer: b) Mechanical energy into electrical energy
16. Alternating current changes its direction after equal intervals of:
a) Distance
b) Time
c) Speed
d) Voltage
Answer: b) Time
17. The frequency of AC supply in India is:
a) 25 Hz
b) 60 Hz
c) 50 Hz
d) 100 Hz
Answer: c) 50 Hz
18. Which wire in domestic circuit is usually green in colour?
a) Live wire
b) Neutral wire
c) Earth wire
d) Fuse wire
Answer: c) Earth wire
19. An electric fuse works on the principle of:
a) Magnetic effect
b) Heating effect of current
c) Chemical effect
d) Electromagnetic induction
Answer: b) Heating effect of current
20. Overloading in an electric circuit occurs when:
a) Voltage is low
b) Too many appliances are connected
c) Fuse wire is thick
d) Switch is off
Answer: b) Too many appliances are connected
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