Concept #1: Transformers

Practice: An outlet in North America outputs electricity at 120 V, but a typical laptop needs to operate at around 20 V. In order to do so, a transformer is placed in a laptop’s power supply. If the coil in the circuit connected to the laptop has 20 turns, how many turns must the coil in the circuit with the outlet have?

You need a transformer to reduce a voltage of 150 V in the primary circuit to 25 V in the secondary circuit. The primary circuit has 130 windings and the secondary circuit is completed through a 55 Ω resistor. How many windings should the secondary circuit contain?

You need a transformer to reduce a voltage of 150 V in the primary circuit to 25 V in the secondary circuit. The primary circuit has 130 windings and the secondary circuit is completed through a 55 Ω resistor. What is the effective resistance of the secondary circuit?

Consider an ideal transformer consisting of a primary coil of N 1 = 240 turns and a secondary coil of an unknown number of turns, N2 as shown below. The primary coil is connected to a function generator, which is set to produce a sinusoidal peak-to-peak voltage of 16 V. Using Using the oscilloscope, a student measures the peak-to-peak voltage difference across the secondary coil to be 56 V. What is N2?
a) 70
b) 720
c) 840