Properties and Applications of Magnets

Properties of Magnets

• Magnets attract iron and iron-like materials.
• Every magnet has two poles: North and South.
• Like poles repel each other.
• Unlike poles attract each other.
• A freely suspended bar magnet aligns itself in a north-south direction, with its north pole pointing north.

Magnetic Fields

• A magnetic field is a region around a magnet where a magnetic force can be felt.
• Magnetic field lines represent the direction of the magnetic force.
• Field lines emerge from the north pole and converge at the south pole.
• Inside the magnet, field lines flow from the south pole to the north pole, forming closed loops.
• The density of field lines indicates the strength of the magnetic field.

Interaction of Magnetic Fields and Electric Currents

• An electric current creates a magnetic field.
• The direction of the force exerted on a conductor in a magnetic field is determined by the directions of the current and the magnetic field.
• Fleming's Left-Hand Rule helps to determine the direction of the force on a conductor in a magnetic field.

Applications of Magnetism

• Magnetic Resonance Imaging (MRI) uses magnetic fields to create images of internal organs.
• Galvanometers detect the presence of current in a circuit and indicate its direction.

Domestic Electric Circuits

• Domestic circuits use three wires:
  • Live wire (positive): red insulation cover
  • Neutral wire (negative): black insulation cover
  • Earth wire: green insulation cover
• The potential difference between live and neutral wires in India is 220 V.
• The sequence of components in a domestic circuit is: Pole ⇒ Main supply ⇒ Fuse ⇒ Electricity meter ⇒ Distribution box ⇒ Separate circuits

Earth Wire

• An earth wire protects users from electric shock.
• It provides a low resistance path for current to flow in case of a leakage.

Short Circuits and Overloading

• A short circuit occurs when the live wire accidentally comes into direct contact with the neutral wire.
• This reduces the circuit's resistance, potentially leading to overloading.
• Overloading happens when the current drawn exceeds the conductor's capacity.
• Causes of Overloading:
  • Accidental voltage surges.
  • Using multiple appliances on a single socket.

Safety Devices

• Electric fuses interrupt the circuit if the current exceeds a safe limit.
• Earth wires protect against electric shocks.
• MCBs (Miniature Circuit Breakers) are circuit breakers designed to automatically interrupt the flow of current if it exceeds a safe limit.