Electromagnetism — Telangana (SSC) Class 10 Science Solutions (Free)

An electromagnet is a magnet created by passing electric current through a coil of insulated wire wound around an iron core. Construction: Insulated copper wire coiled around soft iron core + power source Differences from permanent magnet: 1. Electromagnet requires electric current to be magnetic; permanent magnet has permanent magnetism 2. Strength of electromagnet can be controlled; permanent magnet has fixed strength 3. Electromagnet can be switched on/off; permanent magnet cannot 4. Electromagnet's polarity can be reversed; permanent magnet's polarity is fixed

Faraday's Law: The induced EMF in a coil is directly proportional to the rate of change of magnetic flux through it. Mathematically: e = -N(dΦ/dt) where e = induced EMF, N = number of turns, dΦ/dt = rate of change of magnetic flux Explanation: When magnetic field through a coil changes, an EMF (voltage) is induced. The negative sign indicates direction (Lenz's Law). Practical example: Moving magnet near coil → magnetic field changes → EMF induced → current flows if circuit is closed

Fleming's Left Hand Rule (Force on current-carrying wire in magnetic field): Thumb = direction of force, Index finger = direction of magnetic field, Middle finger = direction of current Application: Determines force direction in electric motors Fleming's Right Hand Rule (Induced EMF/current in moving conductor): Thumb = direction of motion, Index finger = direction of magnetic field, Middle finger = direction of induced current Application: Determines induced current direction in generators

Construction: • Rectangular coil of insulated copper wire • Placed between two poles of a permanent magnet (N and S) • Connected to a split-ring commutator • Commutator rotates with coil, maintaining circuit contact via brushes Working: Step 1: Current enters coil via commutator Step 2: Magnetic force acts on current-carrying coil (Fleming's Left Hand Rule) Step 3: Coil rotates; commutator switches current direction at each half rotation Step 4: Force always acts in same rotational direction → continuous rotation Principle: Converts electrical energy to mechanical energy

Construction: • Rectangular coil rotating between magnetic poles (N-S) • Slip rings attached to coil ends • Brushes maintain circuit contact with slip rings • External circuit/load connected via brushes Working: Step 1: Coil rotates in magnetic field (mechanical energy input) Step 2: Magnetic flux through coil changes continuously Step 3: Rate of flux change induces EMF (Faraday's Law) Step 4: Induced EMF is sinusoidal: e = e₀sin(ωt) Step 5: Current flows in external circuit Principle: Converts mechanical energy to electrical energy

Difference: DC (Direct Current): Flows in one direction; magnitude constant; produced by batteries, cells AC (Alternating Current): Direction reverses periodically; magnitude varies sinusoidally; produced by generators Advantages of AC over DC: 1. Easy transmission over long distances (voltage can be stepped up/down using transformers) 2. Stepping up voltage reduces current → reduces power loss in transmission (P_loss = I²R) 3. AC motors are simpler, cheaper, more efficient than DC motors 4. Easier to generate in bulk using generators

Magnetic field is the region around a magnet where magnetic force can be experienced by another magnet or current-carrying conductor. Cause of magnetism in bar magnet: At atomic level, electrons possess spin and orbital motion → generate tiny magnetic moments In permanent magnet materials (iron, cobalt, nickel): unpaired electrons' magnetic moments align in same direction → net magnetic moment In non-magnetic materials: electron magnetic moments are randomly oriented → cancel each other → no net magnetism Alignment of atomic magnetic moments → aligned domains → material becomes magnet