Important Formulae



Electromagnetism Problems

  1. 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
  2. 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
  3. 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)
  4. 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?
  5. 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
  6. 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
  7. 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

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