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

Click For Summary

Homework Help Overview

The problem involves a transformer connected to a 12V battery, with a resistor on the secondary side. The original poster attempts to calculate the current in the resistor using transformer equations but arrives at a conflicting answer.

Discussion Character

  • Exploratory, Conceptual clarification

Approaches and Questions Raised

  • Participants discuss the nature of transformers and the requirement for AC voltage to induce current in the secondary winding. Questions are raised about the electromagnetic principles that govern transformer operation and the implications of using a DC source.

Discussion Status

Some participants have provided insights into the operation of transformers with DC voltage, noting that a constant current will not produce a changing magnetic field necessary for inducing current in the secondary. There is a recognition of the initial transient response but a lack of consensus on the implications for the problem posed.

Contextual Notes

Participants are considering the assumptions made regarding the type of voltage source and its effects on transformer behavior, particularly the implications of using a DC source instead of AC.

ThirdEyeBlind
Messages
9
Reaction score
0

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?

ekpjX.jpg


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:
Physics news on Phys.org


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.
 

Similar threads

Transformer; make primary voltage x10 of the secondary voltage
  • · Replies 4 ·
Replies
4
Views
2K
Transformers and Electromagnetism
  • · Replies 3 ·
Replies
3
Views
2K
The efficiency of a transformer
  • · Replies 5 ·
Replies
5
Views
3K
How Do You Calculate Primary Current in a Step-Up Transformer?
  • · Replies 2 ·
Replies
2
Views
2K
Why do the headlights on the car become dim when the car is starting?
  • · Replies 4 ·
Replies
4
Views
2K
Transformer question (between substation and home)
  • · Replies 1 ·
Replies
1
Views
1K
Transformer and power question mutiple choice
  • · Replies 7 ·
Replies
7
Views
2K
Calculating turns in a primary coil of a transformer
  • · Replies 2 ·
Replies
2
Views
3K
Does the load on a transformer affect its efficiency?
  • · Replies 3 ·
Replies
3
Views
3K
How Does Efficiency Loss Affect Voltage and Current in a Transformer?
  • · Replies 1 ·
Replies
1
Views
3K