- (a) Motor
- (b) Battery
- (c) Generator
- (d) Switch
Answer:
(a) Motor
- (a) AC only
- (b) DC only
- (c) Both AC and DC
Answer:
(a) AC only
- (a) field magnet
- (b) split rings
- (c) slip rings
- (d) brushes
Answer:
(d) brushes
Slip rings rotate with the coil, while brushes collect current.
- (a) weber
- (b) weber/metre
- (c) weber/metre²
- (d) weber·metre²
Answer:
(c) weber/metre²
Also written as:
SI unit name:
Tesla (T)
- The SI unit of magnetic field induction is tesla.
- Devices used to convert high alternating voltage to low alternating voltage are transformers.
- An electric motor converts electrical energy into mechanical energy.
- A device used for producing electric current is a generator.
| List I | List II |
|---|---|
| Magnetic material | Iron |
| Non-magnetic material | Wood |
| Current and magnetism | Oersted |
| Electromagnetic induction | Faraday |
| Electric generator | Induction |
If false, correct the statement.
Answer: True
Answer: True
If magnetic field lines intersected, magnetic field direction would become ambiguous.
Answer: False
Correct Statement:
Fleming’s Left Hand Rule is called Motor Rule.
Fleming’s Right Hand Rule is associated with generators (dynamo rule).
Answer: False
Correct Statement:
Speed of an electric motor increases by increasing the area of the coil.
Answer: False
Correct Statement:
A transformer works only with alternating current (AC).
Answer: True
Answer:
Stretch the thumb, forefinger, and middle finger of the left hand mutually perpendicular to each other.
- Forefinger → magnetic field
- Middle finger → current
- Thumb → force or motion
This rule gives the direction of motion in an electric motor.
Answer:
The number of magnetic field lines passing normally through unit area is called magnetic flux density.
Where:
- (B) = magnetic flux density
- (\Phi) = magnetic flux
- (A) = area
SI Unit:
or
Answer:
- Field magnet
- Armature coil
- Split ring commutator
- Carbon brushes
- Battery
| Symbol | Part |
|---|---|
| N, S | Permanent magnets |
| ABCD | Armature coil |
| S₁, S₂ | Slip rings |
| B₁, B₂ | Carbon brushes |
Answer:
- AC can be transmitted over long distances with less power loss.
- AC voltage can be stepped up or stepped down easily using transformers.
- Generation cost of AC is lower.
- AC can easily be converted into DC.
| Step-Up Transformer | Step-Down Transformer |
|---|---|
| Increases voltage | Decreases voltage |
| (V_s > V_p) | (V_s < V_p) |
| (N_s > N_p) | (N_s < N_p) |
| Current decreases | Current increases |
| Used in power stations | Used in chargers |
Where:
- (N_s) = turns in secondary coil
- (N_p) = turns in primary coil
Answer:
A portable radio uses a step-down transformer because household AC voltage must be reduced before rectification and use in the radio circuit.
First Law
Whenever magnetic flux linked with a coil changes, an emf is induced.
Second Law
Magnitude of induced emf is directly proportional to rate of change of magnetic flux.
# Principle
A current-carrying conductor placed in magnetic field experiences force.
Direction is determined using Fleming’s Left Hand Rule.
# Construction
Main parts:
- Armature coil
- Field magnet
- Split ring commutator
- Carbon brushes
- Battery
# Working
- Current passes through armature coil.
- Opposite sides of coil experience opposite forces.
- Coil rotates.
- Split ring reverses current every half rotation.
- Continuous rotation is produced.
Thus electrical energy converts into mechanical energy.
# Step-Up Transformer
- Converts low voltage AC into high voltage AC
- Secondary coil has more turns
# Step-Down Transformer
- Converts high voltage AC into low voltage AC
- Secondary coil has fewer turns
Construction
AC generator consists of:
- Rectangular armature coil
- Permanent magnet
- Slip rings
- Carbon brushes
- Axle
Working
- Coil rotates in magnetic field.
- Magnetic flux linked with coil changes.
- Induced current is produced.
- Direction changes every half rotation.
- Thus alternating current is obtained.
Direction of induced current is determined using:
Fleming’s Right Hand Rule
Magnetic Field Around Magnet
Observation:
Paper clips jump and stick to magnet before touching it.
Conclusion:
Magnet produces invisible magnetic field around it.
Magnetic Field Around Current Carrying Conductor
Observation:
Compass needles form concentric circles around conductor.
Conclusion:
Current carrying conductor produces magnetic field.
Direction changes when current direction reverses.
Making an Electromagnet
Observation:
Iron nail attracts paper clips when current flows.
Conclusion:
Electric current produces temporary magnetism.
This is called:
Electromagnetism
Electromagnet works only while current flows.
Revise Magnetism and Electromagnetism faster.
Use these expandable textbook answers for homework, quick revision, and exam preparation.