BEE
Unit 1Magnetic circuits A coil of N turns is wound on a cast iron ring which has mean length of 50 cm and its cross section is of 4cm diameter. The current flowing through the coil is 2A, which produces a flux of a 6mWb in the air gap of 2mm length. If the relative permeability of iron is 1000, the number of turns N. (3M) 2. A coil of 2000turns wound uniformly over a nonmagnetic ring of mean circumference of 80 cm and cross-sectional area of 0.6cm2. If the current through the coil is 2 A. CalculateMagnetizing force1)Reluctance2)Total flux3)Flux density (3M or 4M) 3. An iron ring has its mean length of flux path as 60 cm and its cross sectional area as 15cm2. If relative permeability is 500 find the current required to be passed through a coil of 300 turns, wound uniformly around it to produce a flux density of 1.2 tesla. What would be the flux density with the same current, if the iron ring is replaced by air core. (6M) 4. An iron ring has its mean length of flux path is 80 cm and has a circular cross section of 8.5 cm diameter. Air gap of 4 mm is cut in it. A coil of 550 turns is uniformly wound around it and a current of 2.5A passes through it. Calculate the flux produced in the air gap and in the iron ring. If relative permeability of iron is 1050. Ignore leakage and fringing. (6M) 5. A magnetic circuit consist two materials. The core has uniform section of 6 cm2. The core carries a winding with 900 turns. The current in the coil is 3A. Calculate the flux produced in the air gap if the length of the gap is 1mm. relative permeability of material A is 1000 & for B is 1500. The length of the magnetic circuit for A is 80 cm & B is 50 cm. (6M) 6. An iron ring wound with a 500 turns coil, produces a flux density of 0.94T in the ring when current in the coil is 2.4 A. Mean length of iron path is 80 cm and that of the air gap is 1mm. Determine relative permeability of iron. For the above coil Determine:i)Self inductance ii) Energy stored, if cross sectional area is 20 cm2. (6M) 7. A ring composed of three sections. The cross sectional area is 0.001m² for each section. The m mean arc lengths are for part A =0.3m , part B =0.2m , part C=0.1m.An air gap length of 0.1mm is cut in the ring. The relative permeability for the sections A,B,C are 5000, 1000 & 10000 respectively. Flux in the air-gap is 7.5×10-4 Wb. Find 1)mmf 2)Exciting current if the coil has 100 turns 3) reluctance of each section. (6M) 8. A mild steel ring having a cross-sectional area of 500 mm2 and a mean circumference of 400 mm has a coil of 200 turns wound uniformly around it. Assume the relative permeability of mild steel to be 380.Find a) reluctance of ring b) current required to produce a flux of 800 µwb in the ring(6M) 9. A metallic ring of uniform cross-section of 2 cm2 and mean diameter of 20 cm is wound with 1000 turns of wire. When coil carries a current of 1A, the flux in the ring is 240 µwb, calculate i) relative permeability of material ii) Magnetic field strength in two ring. (6M) 
10. An iron ring has a cross-sectional area of 400 mm2 and a mean diameter of 25 cm. It is wound with 500 turns. If value of relative permeability is 250, find the total flux set-up. The coil resistance is 474 
and supply voltage is 240V. (4M) 11. A circular iron ring has a mean circumference of 1.5 m and cross-sectional area of 0.01m2. A saw cut of 4 mm wide is made in the ring. Calculate the magnetizing current required to produce a flux of 0.8 mwb in the air gap if ring is wound with a coil of 175 turns. Assume relative permeability of iron as 400 and leakage factor 1.25 (6M) 12. A laminated soft iron ring has a mean circumference of 600 mm, cross-sectional area= 500 mm2, air gap of 1 mm, coil turns=1000. Estimate the current in the coil to produce flux density of 0.5 mwb in the air gap assuming i) leakage factor is 1.2 ii) space factor=0.9 (useful iron area) iii) µr for soft iron 1000(6M) 13. An iron ring of circular cross-sectional area of 3 cm2 and mean diameter of 20 cms. A coil of 500 turns of wire carries a current of 2.09 A to produce the magnetic flux of 0.5 mwb in the ring. Determine permeability of material. Mean length = 60 cm, A = 2.826 X 10-3 m2 N =700 turns, I = 2A, µr =1000 find flux produce in the air gap and in the ring. (6M) 14. A ring having mean diameter of 21 cm and a cross-sectional area of 10 cm2 is made up of semicircular sections of cast iron and cast steel with each joint having reluctance equal to an airgap of 0.2 mm. Determine ampere-turns required to produce a flux of 0.8 mwb.µr cast iron =166 µr cast steel 800 (6M) 15. A coil of 150 turns is linked with a flux of 0.01wb when carrying a current of 10A. Calculate the inductance of the coil. If current is uniformly reversed in 0.01 s, calculate the emf induced. (6M) 16. An air cored torioidal coil of 600 turns has axial length of 60 cm and diameter of 4 cm. Calculateself inductance of coil ii) emf induced in the coil if a current of 10A is interrupted in 1 msec. iii) energy stored in magnetic field of coil when it carries current of 10A. (6M) Two coils having 400 and 800 turns are wound on a common magnetic ring having mean length of 80 cm and a uniform cross-section of 10 cm2 µr ring = 1000, find i) self inductance of each coil ii) mutual inductance between the coils, assume perfect magnetic coupling. (6M) Two coils A & B have 1800 & 1200 turns respectively. 60% of flux produced by coil A links with coil B. A current of 1A in coil produces a flux of 150 µwb findi) self inductance of coil A & Bii)Mutual inductanceiii) Coefficient of coupling, emf induced in coil A & B when the current in coil A is switched off in 10ms. (6M) 
The number of turns in two coupled coil is 600 and 1700 respectively. When current of 6A flows in the second coil. The total magnetic flux produced in this coil is 0.8 mwb and flux that links with the first coil is only 0.5 mwb. Calculate L 1 , L 2 , K , (6M)
10. An iron ring has a cross-sectional area of 400 mm2 and a mean diameter of 25 cm. It is wound with 500 turns. If value of relative permeability is 250, find the total flux set-up. The coil resistance is 474 and supply voltage is 240V. (4M) 11. A circular iron ring has a mean circumference of 1.5 m and cross-sectional area of 0.01m2. A saw cut of 4 mm wide is made in the ring. Calculate the magnetizing current required to produce a flux of 0.8 mwb in the air gap if ring is wound with a coil of 175 turns. Assume relative permeability of iron as 400 and leakage factor 1.25 (6M) 12. A laminated soft iron ring has a mean circumference of 600 mm, cross-sectional area= 500 mm2, air gap of 1 mm, coil turns=1000. Estimate the current in the coil to produce flux density of 0.5 mwb in the air gap assuming i) leakage factor is 1.2 ii) space factor=0.9 (useful iron area) iii) µr for soft iron 1000(6M) 13. An iron ring of circular cross-sectional area of 3 cm2 and mean diameter of 20 cms. A coil of 500 turns of wire carries a current of 2.09 A to produce the magnetic flux of 0.5 mwb in the ring. Determine permeability of material. Mean length = 60 cm, A = 2.826 X 10-3 m2 N =700 turns, I = 2A, µr =1000 find flux produce in the air gap and in the ring. (6M) 14. A ring having mean diameter of 21 cm and a cross-sectional area of 10 cm2 is made up of semicircular sections of cast iron and cast steel with each joint having reluctance equal to an airgap of 0.2 mm. Determine ampere-turns required to produce a flux of 0.8 mwb.The number of turns in two coupled coil is 600 and 1700 respectively. When current of 6A flows in the second coil. The total magnetic flux produced in this coil is 0.8 mwb and flux that links with the first coil is only 0.5 mwb. Calculate L 1 , L 2 , K , (6M)
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