Transformers

The current in the secondary coil of a step-up transformer is 0.86 A when the current in the primary coil is 4.8 A. Determine the turns ratio, N_s/N_p, of the transformer.

• 5.6

• 4.1

• 0.24

• 0.18

• 0.12

Which one of the following statements concerning transformers is false?

• Their operation makes use of mutual induction.

• They are an application of Faraday's and Lenz's laws.

• A transformer can function with either an ac current or a steady dc current.

• A transformer that steps down the voltage, steps up the current.

• A transformer that steps up the voltage, steps down the current.

A transformer changes 120 V across the primary to 1200 V across the secondary. If the secondary coil has 800 turns, how many turns does the primary coil have?

• 40

• 80

• 100

• 400

• 4000

A transformer has 450 turns in its primary coil and 30 turns in its secondary coil. Which one of the following statements concerning this transformer is true?

• This is a step-up transformer.

• The turns ratio is 15 for this transformer.

• The ratio of the voltages Vs / Vp is 15 for this transformer.

• The ratio of the currents Is / Ip is 0.067 for this transformer.

• The power delivered to the secondary must be the same as that delivered to the primary.

A small power plant produces a voltage of 6.0 kV and 150 A. The voltage is stepped up to 240 kV by a transformer before it is transmitted to a substation. The resistance of the transmission line between the power plant and the substation is 75 Ohm.

What is the current in the transmission line from the plant to the substation?

• 3.8 A

• 5.2 A

• 6.4 A

• 7.0 A

• 7.5 A

A small power plant produces a voltage of 6.0 kV and 150 A. The voltage is stepped up to 240 kV by a transformer before it is transmitted to a substation. The resistance of the transmission line between the power plant and the substation is 75 Ohm.

What percentage of the power produced at the power plant is lost in transmission to the substation?

• 0.47 %

• 0.41 %

• 0.34 %

• 0.23 %

• 0.12 %