# 437 electromagentics i 1

Electromagnetics I

1. Discuss in detail 4 applications of Biot-Savart Law (25mks)

2. A current of 15 A is passing along a straight wire. Calculate the force on a unit
magnetic pole placed 0.15 metre from the wire. If the wire is bent to form into a loop, calculate the
diameter of the loop so as to produce the same force at the centre of the coil upon a unit magnetic
pole when carrying a current of 15 A

3. A ring has a diameter of 21 cm and a cross-sectional area of 10 cm2. The ring
is made up of semicircular sections of cast iron and cast steel, with each joint having a reluctance
equal to an air-gap of 0.2 mm. Find the ampere-turns required to produce a flux of 8 × 10−4 Wb. The
relative permeabilities of cast steel and cast iron are 800 and 166 respectively.
Neglect fringing and leakage effects

4. A cast steel d.c. electromagnet shown in Fig. 6.37 has a coil of 1000 turns on its
central limb. Determine the current that the coil should carry to produce a flux of 2.5 mWb in the
air-gap. Neglect leakage. Dimensions are given in cm. The magnetisation curve for cast steel is as
under :
Flux density (Wb/m2) : 0.2 0.5 0.7 1.0 1.2
Amp-turns/metre : 300 540 650 900 1150