Multiple Choice
A transformer has 200 turns in the primary and 25 turns in the secondary. If the primary is hooked up to a household outlet, what is the potential across the secondary coil?
30. Induction and Inductance
Transformers
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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?
A
3 turns
B
6 turns
C
20 turns
D
120 turns
Verified step by step guidance1
Understand that a transformer is used to change the voltage from one level to another using two coils: the primary coil (connected to the power source) and the secondary coil (connected to the device).
Recall the transformer equation: \( \frac{V_p}{V_s} = \frac{N_p}{N_s} \), where \( V_p \) and \( V_s \) are the primary and secondary voltages, and \( N_p \) and \( N_s \) are the number of turns in the primary and secondary coils, respectively.
Identify the given values: \( V_p = 120 \text{ V} \), \( V_s = 20 \text{ V} \), and \( N_s = 20 \text{ turns} \). We need to find \( N_p \).
Rearrange the transformer equation to solve for \( N_p \): \( N_p = \frac{V_p}{V_s} \times N_s \).
Substitute the known values into the equation: \( N_p = \frac{120}{20} \times 20 \). Calculate this to find the number of turns in the primary coil.
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