## Electromagnetism

### Important Formulae

## Topic

## Electromagnetism Problems

- An iron ring has a mean circumference of 50cm and a cross sectional area of 4cm^2 it is wound with 600 turns of wire if the μ_r of iron is 400. Calculate the inductance of the coil and the energy stored in the magnetic field if the current flowing through the coil is 10A
- A coil of 500 turns wound on a core of non-magnetic material (μ_r=1) has an inductance of 9mH. Calculate (a) the flux produced by a current of 10A (b) the average value of EMF induced when the current is reversed in 10ms
- Find the inductance of a coil of 200 turns wound on a paper core tube of 25 cm length and 5 cm radius. Also calculate energy stored in it if current rises from zero to 5A. (μ_r for paper=1)
- The winding of an electromagnet is wound with 96 turns and has a resistance of 56 ohms, the exciting voltage if 250 V and flux linking the coil is 5 mwb. Find the energy stored in magnetic field, if the current is reversed in 0.1 and what emf is induced in the coil?
- A coil of 150 turns is linked with a flux of 0.01 wb when carrying a current of 10A. Calculate the inductance of the coil if the current is uniformly reversed in 0.01 sec. Calculate the induced EMF
- A coil of 1000 turns is wound on a ring of silicon steel having mean diameter of 10cm and relative permeability 1200. Its cross-sectional area is 12 sq cm when a current of 5A flows through the coil. Find (i) Flux in the core (ii) Inductance of the coil (iii) Induced emf if the flux falls to zero in 20m sec
- Calculate the approximate resistance and inductance of an air cored solenoid of mean diameter of 1 cm, 1m long wound with 1000 turns of copper wire, 0.5 mm in diameter. What potential difference exists between the terminals of the solenoid at the instant when the current is 1 A and increasing at the rate of 10,000 A/s. Take the resistivity of copper as 1.72 x 10^-8 ohms/m