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Exercise Solution

 

Question 1

 

The advantage of making N (number of turns) large is that the emf and induced current are proportional to N, which makes it easier to experimentally measure those quantities.

 

Question 2

 

1.  The magnetic flux is proportional to the total number of field lines that pass through an enclosed loop area. FB = BAcosq

      The flux, therefore, is proportional to the magnitude of the magnetic field.

2.  They have different units (Tesla for magnetic field, and Wb for magnetic field.

3.  Magnetic field is a vector (size and direction) while magnetic flux is a scalar (size)

 

Problem 1

 

The average induced emf is given by (equation 21-2b)

 

E = -ND FB /Dt = -2(38 Wb) - (-50 Wb)/0.42 s = -420 V

 

 

Problem 20

 

The number of turns can be found using equation 21-5. 

The factor multiplying the sine term is the peak output voltage.

Epeak = NB wA = 24.0V/(0.420 T)(2p rad/rev)(60 rev/s)(0.060 m)2 @ 42 loops

 

 

Problem 31

Since Ns < Np we know that this is a step down transformer.

We can use equation 21-6 to find the voltage ratio and equation 21-7 to find the current ratio.

Vs/Vp = Ns/Np = 120 turns/320 turns = 0.375

Is/Ip = Np/Ns = 320 turns/120 turns = 2.67