Class 10 · Chapter 12 · Physics
Magnetic Effects of Electric Current Cheat Sheet
Definitions
- Magnetic field
- The region around a magnet or a current-carrying conductor in which its magnetic force can be detected.
- Magnetic field lines
- Curved lines used to represent a magnetic field; their direction gives the field direction at each point.
- Solenoid
- A coil of many circular turns of insulated copper wire, which behaves like a bar magnet when current flows.
- Electromagnet
- A temporary magnet made by winding a coil around a soft iron core and passing current through it.
- Electric motor
- A device that converts electrical energy into mechanical energy.
- Commutator
- A split ring that reverses the direction of current in the coil of a motor every half rotation.
- Armature
- The part of a motor or generator that rotates between the magnetic poles.
- Electromagnetic induction
- The production of a current in a conductor by changing the magnetic field around it.
- Induced current
- The current produced in a conductor by electromagnetic induction.
- Electric generator
- A device that converts mechanical energy into electrical energy.
- Alternating current
- A current that reverses its direction periodically; used in domestic supply.
- Direct current
- A current that flows in only one direction.
- Live wire
- The wire at high potential that brings current into a circuit; insulation is red or brown.
- Neutral wire
- The wire at near-zero potential that completes the circuit; insulation is black or blue.
- Earth wire
- The safety wire connected to the ground that carries leakage current to the earth; insulation is green.
- Short circuit
- A condition in which the live and neutral wires touch directly, causing a sudden large current.
- Overloading
- A condition in which too many appliances draw a current greater than the circuit can safely carry.
Key Points
- The magnetic field of a bar magnet is strongest near the poles; field lines never intersect and are closed curves.
- Oersted discovered that a compass needle deflects when current flows through a nearby wire, showing that a current produces a magnetic field.
- Right-hand thumb rule: if the thumb of the right hand points along the current, the curled fingers give the direction of the magnetic field.
- A current-carrying circular loop and a solenoid behave like magnets; a solenoid with a soft iron core makes an electromagnet.
- A force acts on a current-carrying conductor placed in a magnetic field; the magnitude is largest when the conductor is perpendicular to the field.
- Fleming’s left-hand rule gives the direction of the force: forefinger — field, middle finger — current, thumb — force. It is used for the electric motor.
- An electric motor converts electrical energy into mechanical energy; the split ring (commutator) reverses the current every half rotation.
- Electromagnetic induction: moving a magnet near a coil or a coil near a magnet induces a current; Fleming’s right-hand rule gives its direction.
- An electric generator converts mechanical energy into electrical energy; a.c. generators use slip rings and d.c. generators use a split ring.
- In domestic wiring, the live (red/brown), neutral (black/blue) and earth (green) wires are used; a fuse and earthing protect against overloading and short circuits.