Problem 33.43 Electricity is distributed from electrical substations to neighbor

Question

Problem 33.43 Electricity is distributed from electrical substations to neighborhoods at 1.6x10^4V . This is a 60Hz oscillating (AC) voltage. Neighborhood transformers, seen on utility poles, step this voltage down to the 120V that is delivered to your house. Part A How many turns does the primary coil on the transformer have if the secondary coil has 100 turns? Express your answer using two significant figures. Part B No energy is lost in an ideal transformer, so the output power Pout from the secondary coil equals the input power Pin to the primary coil. Suppose a neighborhood transformer delivers 270A at 120 V. What is the current in the 1.6x10^4V line from the substation? Express your answer using two significant figures.

Explanation / Answer

Note that

n_primary = Vprimary (n_secondary)/V_secondary

As Vprimary = 1.6E4 V,
n_secondary = 100
Vsecondary = 120 V,

Thus,

n_primary = 1.33E4 turns [ANSWER]

*****************************

Pout = Pin

Since P = IV,

Iout Vout = Iin Vin

As Vout = 120 V
I out = 270 A
V in = 1.6E4

Thus,

Iin = 2.025 A [ANSWER]

DONE! It was nice working with you!

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