Magnet
Magnet is an object which attracts pieces of iron, steel etc. towards itself.
Magnet are different shape:
- Bar Magnet
- Horse shoe shaped magnet
- Magnetic needle
- Magnetic compass
Some Facts About Magnets
1. Magnet always exist as dipole.
2. When magnet is freely suspended it always aligns towards north-south direction.
3. Like pole always repel and opposite poles attract each other.
4. Two poles can never be separated.
Oersted’s Experiment
Magnetic Field Lines
Imaginary lines which represents magnetic field around a magnet, are called magnetic field lines.
Properties of Magnetic Field Lines
1. Magnetic field lines always originate from north pole and terminate at South pole.
2. Magnetic Field lines are always closed curve.
3. Two magnetic field lines never cross each other.
4. Magnetic field lines is strong if they are closer and vice-versa.
5. Tangent to magnetic field lines shows direction of field.
Note: Magnetic field is studied by drawing imaginary lines called magnetic lines of forces.
Right Hand Thumb Rule
If we hold a wire with our right hand and keep our thumb in the direction of the current flowing in the wire, then the bent fingers show the direction of the magnetic field generated due to the current.
Magnetic Field due to Straight
Shape of magnetic field for straight wire is in the form of concentric circles having centre as its conductor.
Factor affecting magnetic field for straight conductor:
1. Current: Magnetic field strength is directly proportional to the amount of current flowing in conductor.
2. Distance: Magnetic field strength is inversely proportional to the distance from conductor.
3. Direction of current: If direction of current changes, if changes the direction of magnetic field.
Magnetic Field due to Current Carrying Circular Loop:
Factor affecting magnetic field for circular loop:
1. Current in the loop: Magnetic field is directly proportional to the current in the loop.
2. Radius of loop: Magnetic field is inversely proportional to the radius of loop for same current.
3. Distance from loop: Magnetic field is inversely proportional to the distance from loop.
Magnetic Field Produced due to Solenoid
Factors affecting magnetic field of solenoid
1. Current in Solenoid: magnetic field is directly proportional to the current flowing in solenoid.
2. Number of turns in solenoid: Magnetic field is directly proportional to the number of turns per unit length.
3. Distance from solenoid: Magnetic field is inversely proportional to the distance from the solenoid.
Electromagnet
A strong magnetic field produced inside a solenoid can be used to magnetise a piece of magnetic material, like soft iron, when placed inside the coil. The magnets so form is called an Electromagnet.
Difference between Permanent Magnet and Electromagnet
Fleming’s left hand rule
Force on a current-carrying conductor in magnetic field:
French scientist Andre Marie Ampere suggest that whenever current carrying conductor is placed inside an external magnetic field, it experiences a force which is perpendicular to the both magnetic field and current.
Reason of Force: Conductor produces its own magnetic field and this magnetic field interact with external magnetic field and hence conductor experiences force.
Fleming’s Left Hand Rule:
If we stretch our fore finger, middle finger and thumb mutually perpendicular to each other such that fore finger points in the direction of magnetic field middle finger indicates direction of current then thum give the direction of force.
Domestic Electric Circuit
Earthing
Electric appliances are always touched by hands, there can be a chance that its insulation breaks or cracks, them its bare wires touches its metal cases than the person touching them might get a shock. To avoid such the metal cases are earthed.
By earthing we mean that the metallic body is connected to thick copper wire which is buried deep under earth. And at the end of copper plate is surrounded by mixture of charcoal and common salt.
The earth is always at 0 potential. So, if an electric appliance gets short circuit metal body to the earth like if magnitude of current rises due to short circuit the fuse wire melts but the appliance will not receive any current as it is earthen.
Important Definition
Overloading
Overloading of an electric circuit means when current flows in a circuit it becomes more than the capacity of components in the circuit to resist the current. When too much current passes in an electric circuit, overload occurs through electric wires, which may cause fire to break.
Note: Fuse and MCB are used to avoid overloading.
Short-Circuiting
A short circuit is an electrical circuit that allows a current to travel along an unintended path with very low electrical resistance. This results in an excessive current flowing through the circuit, which may cause fire to break.
Note: We should keep checking the insulation to avoid short circuit.
Question: What is advantageous to use domestic circuit in parallel than series.
Answer:
Independent Operation: Appliances work independently; one failure doesn’t affect others.
Equal Voltage: All appliances receive the same voltage as the supply.
Varied Current: Different appliances can draw the required current.
Energy Efficient: Appliances can be used individually, saving energy.Safety: Reduces overheating risks.
Difference between AC and DC
| Alternates direction periodically. | DC: Flows in one constant direction. |
| Generated by power plants (e.g., mains electricity). | Provided by batteries, solar cells. |
| Can be easily transformed to different voltages. | Difficult to change voltage. |
| Used for homes and industries. | Used in electronic devices and vehicles. |
| Efficient for long-distance transmission. | Less efficient over long distances. |
Kicking Wire Experiment
On pressing the switch current flows in wire in downward direction as it is placed between poles of magnet because force acts on it and wire gets displaced from its original position.
As it gets displaced, circuit breaks, current flows stops due to which no force acts on wire and it returns to its original position.
Again circuit gets completed, again force acts and wire get displaced.
This is how it goes on repeating.