# Transformers and power transmission

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##### Intros

##### Examples

###### Lessons

- An ideal transformer with 120V, ac supply, on the primary coil supplies power to the resistor R. If this resistor dissipates 35W, what is the current in the primary coil and the secondary coil?
- The secondary coil in an ideal transformer has 5 times as many windings as the primary. If the current in the primary is 0.40A, determine the current in the secondary, and the type of the transformer.
- A certain step-down transformer has a 500-turns primary that operates at 120V ac supply. Which one of the following sets of conditions could describe the secondary turns and voltages of this transformer?
- A step-down transformer is required to operate a 12 V, 25 W halogen lamp. Which of the following sets of conditions could apply to this transformer?
- $N_{p} = 20, \qquad N_{s} = 200$
- $V_{p} = 120V, \qquad I_{s} = 0.21 A$
- $I_{p} = 2.1 A, \qquad I_{s} = 2.1 A$
- $V_{p} = 120V, \qquad I_{p} = 0.21 A$

- An ideal transformer has a potential difference of 130V ac across the primary windings and a potential difference of 780V ac across the secondary windings. There are 390 turns in the secondary. The secondary current is
- twice the primary current
- one half the primary current
- six times the primary current
- one-sixth the primary current