CHAPTER 20 QUIZ

TRANSFORMERS

1. How is energy transferred from the primary to the secondary of a transformer?

2. Suppose d.c. were fed into the primary of a transformer, what would happen?

3. Explain how the secondary current controls the amount of primary current?

4. A welding transformer has a one-turn secondary that delivers 400 amperes. The primary
    has 800 turns. What is the primary current?

5. You want to build a transformer to step-down 440 volts to 110 volts. If 2,080 turns are
    used on the secondary, how many turns will be used on the primary?

6. A loaded secondary draws 80 amperes at 220 volts. If the primary is 600 volts, what is
    the primary current?

7. A 440/110 volt transformer is designed for 1/4 volt per turn. How many turns on
    primary and secondary?

8. Is it absolutely correct to say that transformers ate 100 percent efficient?

9. Two losses occur in a transformer? What are they?

10. How can the losses of a transformer be reduced?

CHAPTER 20 ANSWERS

TRANSFORMERS

1. The magnetic flux field set up by the primary current carries the primary's energy
    to the secondary.

2. D.c. produces no continuous voltage of self induction, therefore a very high current
    would flow. The primary would burn out.

3. The secondary's flux field cancels the primary's. This reduces the E_si in the primary and
    adjusts primary current in exact proportions to the secondary current.

4. 1/2 ampere.

5. 8320 turns.

6. 29-1/3 amps.

7. 1,760 and 440 turns.

8. No.

9. Iron losses - hysteresis and eddy currents. Copper losses - resistance.

10. Iron, by using soft iron or silica steel in laminated form.  Copper; by shortening the
      length per turn, and using heavy wire. Both, by cooling entire assembly.