Two similar coils are placed near each other. When the current in one coil is ch

Question

Two similar coils are placed near each other. When the current in one coil is changed from 1.2 A to 4.7 A in a time 0.005 s, an emf with a magnitude of 4.6 V is produced in the other coil. The mutual inductance of the coils is closest to: (a) 2.2 mH (b) 3.3 mH (c) 4.4 mH (d) 5.5 mH (e) 5.6 mH In a transformer, the primary coil has 180 turns and the secondary coil has 36 turns. The primary coil is connected to 110 V ac source and draws 4.4 W of power. The current in the secondary is closest to: (a) 0.20 A (b) 8.0 times 10^-3 A (c) 0.40 A (d) 1.6 times 10^-2 A (e) 0.30 A

Explanation / Answer

(7).emf E = 4.6 volt

Change in current di = 4.7 A - 1.2 A

                             = 3.5 A

time interval dt = 0.005 s

We know E = M di / dt

From this mutual inductance M = E(dt) / di

                                             = 4.6(0.005)/3.5

                                            = 6.57x10 -3 H

                                           = 6.57 mH

                                           = 6.6 mH ( two significant figures)

(8).Number of truns in primary N = 180

Number of truns in secondary N ' = 36

Voltage in primary V = 110 volt

Voltage in secondary V ' = ?

Power in Primary P = 4.4 W

                    V i = 4.4 W

Current in primary i = 4.4 / 110

                            = 0.04 A

We know i ' / i = N / N '

From this i ' = ( N / N ') i

                  = (180/36) 0.04

                  = 0.2 A

                                                                                            

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