Battery with voltage V=12V is connected to the primary of a transform

AI Thread Summary
A 12V battery connected to the primary of a transformer with 200 turns on the primary and 600 turns on the secondary leads to the calculation of secondary voltage as 36V. However, the current in the resistor connected to the secondary is zero because transformers require alternating current (AC) to operate effectively. When a direct current (DC) is applied, it results in a constant primary current after an initial transient, which does not create a changing magnetic field necessary for inducing current in the secondary. Therefore, the calculations do not account for the fundamental operation of transformers with DC sources. Understanding that transformers only function with AC is crucial to resolving the confusion about the current in the secondary.
ThirdEyeBlind
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Homework Statement


A battery with voltage V=12V is connected to the primary of a transformer. A resistor with resistance R =20 Ohms is connected to the transformer secondary. The transformer has an iron core with Np=200 turns on the primary and Ns=600 turns on the secondary. Assume the resistance of the wires is zero.

What is Is, the current in the resistor?

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Homework Equations


Vs= (Ns/Np)Vp
V=IR

The Attempt at a Solution


Vs=(600/200) * 12 V
Vs=36 V

V=IR

36V=I(20 ohms)
I =1.8A, but the answer is 0? Could someone please show me where I have made my error or how to arrive at the answer of 0 A?
 
Last edited:
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Transformers require AC to operate. A DC voltage source on the primary will just run a DC current through the primary (limited by the primary's resistance). After any initial transient response when the voltage is first connected the current in the primary will be constant, so there will be no changing magnetic field to influence the secondary. So after an initial 'glitch' there will be no current in the secondary.
 


The answer dies not lie in calculations.
Do you know any of the electromagnetic theory behind a transformer?
What is it that causes a current in the secondary winding?
What is the nature of the current in the primary that causes that?
 


gneill said:
Transformers require AC to operate. A DC voltage source on the primary will just run a DC current through the primary (limited by the primary's resistance). After any initial transient response when the voltage is first connected the current in the primary will be constant, so there will be no changing magnetic field to influence the secondary. So after an initial 'glitch' there will be no current in the secondary.
Thank you for the quick response and explanation. I now understand.
 

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