Transformers MOD V 1.1

Name each type of transformer efficiency.

*I2R - copper loss inherent resistance minimized by using lg diameter wire & increasing voltage & decreasing amperage *Hysteresis loss - lagging energy changes as magnetism changes residual magnetism = lag = heat loss minimized by using silicon iron *Eddy current loss result of currents opposing the cause which produced them Lenz's law

Explain mutual induction in transformers.

AC supplied to primary coil lines of force provide motion induced current to secondary coil AC ONLY

What does a capacitor do?

Accumulates & stores electrical energy. Relates to mobile units.

Name each of the transformer configurations.

Air core Open core Closed core Shell-type

Why must all transformers operate on AC?

All transformers must operate on AC to provide the moving lines of the magnetic fields that induce voltage on the 2nd coil

What is the transformer law?

Expresses the step-up and step-down phenomena V(s)/V(p) = N(s)/N(p)

What is a step-down transformer?

Step-down: decrease voltage, increase amperage

What is a step-up transformer?

Step-up: increased voltage, decrease amperage

What do autotransformers do?

Vary input voltage to control output voltage. Connects primary and secondary into a series.

Relationships of voltage, amperage, and number of turns.

Voltage & amperage: inversely proportional Voltage & number of turns: directly proportional Amperage & number of turns: inversely proportional

A transformer operates: a. on AC but not on DC b. on both DC and AC c. on DC but not AC d. only above its critical current e. only on a constant voltage

a. on AC but not on DC

The turns ratio is defined as: a. secondary windings / primary windings b. primary iron core / secondary iron core c. primary voltage / secondary voltage d. primary windings / secondary windings e. secondary current / primary current

a. secondary windings / primary windings

A transformer with a turns ratio of 1000:1 is a. a step-down transformer b. a step-up transformer c. an autotransformer d. used to increase current e. used to reduce voltage

b. a step-up transformer

What is the transformer that looks like a square donut called? a. auto b. closed-core c. high-frequency d. induction e. shell-type

b. closed-core

Primary to secondary coupling in a transformer is enhanced by: a. 60 Hz b. AC c. an iron core d. DC e. EMF

c. an iron core

Which of the following statements about transformers is correct? a. if there were equal numbers of primary and secondary coil turns, the turns ratio would be zero. b. in the shell-type transformer, the primary and secondary coils are would on different coils c. laminated transformer coils are more efficient than unlaminiated ones. d. the autotransformer controls current. e. the high-voltage transformer in an x-ray imaging system is the autotransformer.

c. laminated transformer coils are more efficient than unlaminated ones.

When a step-up transformer is in use: a. the primary winding has more turns than the secondary winding b. the secondary current is greater than the primary current c. the secondary voltage is greater than the primary voltage d. x-ray tube current is selected e. the turns ratio is equal to 1

c. the secondary voltage is greater than the primary voltage

When a transformer is designed, the change in current is: a. dependent on the supply voltage b. directly proportional to the voltage change c. in the same direction as the voltage change d. inversely proportional to the turns ratio e. proportional to the turns ratio

d. inversely proportional to the turns ratio

The output current in a step-up transformer is: a. higher than the input current b. independent of the input current c. independent of the turns ratio d. lower than the input current e. the same as the input current

d. lower than the input current current = amperage question is not asking about voltage!

Transformers have iron cores to intensify the: a. electric current b. electric potential c. electric power d. electric voltage e. magnetic field

e. magnetic field

If DC is applied to the primary coil of a step-up transformer, what is the result in the secondary coil? a. AC b. increased current c. increased magnetic field d. increased voltage e. nothing

e. nothing

The transformer changes: a. electric current to voltage b. electric energy to electromechanical energy c. electric energy to mechanical energy d. mechanical energy to electric energy e. the amplitude of the voltage

e. the amplitude of the voltage

A transformer "transforms" or changes electric: a. frequency b. impedence c. power d. resistance e. voltage

e. voltage