# Vs/Vp = Ns/Np This apply in transformer.

• 7bear
In summary, the voltage ratio in a transformer is usually larger than the turns ratio, as not all magnetic field lines from the primary coil cut the secondary coil due to the leakage inductance. This means that some field lines go to the surroundings, resulting in a lower primary impedance when the secondary is unloaded. The transformer can be understood through its equivalent circuit, which includes an 'L' of inductances representing the leakage inductance and the main primary inductance. At high frequencies, the leakage inductance becomes more significant. However, understanding all the aspects of a transformer can take a long time.
7bear
Vs/Vp = Ns/Np
This apply in transformer.
But I have read the following statement :
' Uasally , voltage ratio is larger than the turns ratio. This is because not all field lines from primary coil cut the secondary coil.'
Why? Is that mean some field lines 'go' to surroundings?

I am no expert, but from what i understand the magnetic field, shown by the field lines, is *mostly* confined to the iron frame or whatever. mostly, as in not all, so that may explain it. am I right? this is more of an educated guess rather than a real solution

Well I'm no expert either and would love some answers on my thread in the EE section but here goes.

The primary will indeed generate a magnetic field, but since there is no perfect copuling some of the lines are not intercepted by the secondary. In the transformer model I'm reading about the author modeled it as the "leakage inductance" and its in series with the secondary. He assigns the leakage inductance as being the culprit for not having an infinite primary impedance when the seconday is unloaded.

The last statement is not true -- impedance in the AC sense is dependant upon L and frequency . The best way to understand the transformer is via it's equivalent circuit
Unfortunately a real transformer is a very complex animal and it is best to take it a bit at a time . First ignore any resistance , second ignore any capacitance just deal with inductive aspects .
It is true that not all the magnetic flux from the primary links the secondary ( with cored transformers it may not be much ) but it does exist and effects high frequency performance .
The simplest equivalent is an 'L' of inductances i.e. one series element and one parallel followed by a perfect transformer.
The series element represents the 'leakage inductance ' it can be measured
by a short circuit applied to the secondary , the parallel element is the main primary inductance as measured by an open circiuit . These values are good
if Ls << Lp . From this it can be seen that at high frequencies Ls may
become important .
I have to give you a warning -- it can take the best part of a lifetime to understand all the vagaries of this beast.
Yours Ray.

Ps for those interested in how to post diagrams this is a 60 dpi Jpeg originating in Corel Draw -- it is enclosed in a rectangle to make sure that a whole page ( letter is not posted ) . 60 dpi keeps it small yet visible so as not to waste Forum memory . Ray . ALso notice you do not have to down load this to view just click on the diagram .That is just a jpeg attribute not Cdraw .

#### Attachments

• trans.jpg
6.2 KB · Views: 509
Last edited:

## 1. What does Vs/Vp = Ns/Np mean in a transformer?

This equation is known as the turns ratio in a transformer and it represents the ratio between the number of turns on the primary coil (Vs/Vp) and the number of turns on the secondary coil (Ns/Np). It is used to calculate the voltage transformation in a transformer.

## 2. How is the turns ratio determined in a transformer?

The turns ratio in a transformer can be determined by counting the number of turns on the primary and secondary coils. It can also be calculated by dividing the input voltage (Vs) by the output voltage (Vp) or the number of turns on the primary coil (Ns) by the number of turns on the secondary coil (Np).

## 3. What is the significance of the turns ratio in a transformer?

The turns ratio is important in a transformer as it determines the voltage transformation between the primary and secondary coils. It allows for the transformation of high or low voltage levels to meet the requirements of different electrical systems.

## 4. How does the turns ratio affect the power output of a transformer?

The turns ratio affects the power output of a transformer by determining the voltage and current levels. A higher turns ratio results in a higher voltage output and a lower current output, while a lower turns ratio results in a lower voltage output and a higher current output.

## 5. Can the turns ratio be changed in a transformer?

The turns ratio in a transformer is fixed and cannot be changed without physically altering the number of turns on the primary or secondary coil. However, different turns ratios can be achieved by using transformers with different numbers of turns on the primary and secondary coils.

• Introductory Physics Homework Help
Replies
4
Views
1K
• Other Physics Topics
Replies
1
Views
3K
• Introductory Physics Homework Help
Replies
3
Views
1K
• Introductory Physics Homework Help
Replies
5
Views
2K
• Other Physics Topics
Replies
4
Views
11K
• Other Physics Topics
Replies
17
Views
3K
• Electrical Engineering
Replies
3
Views
2K
• Other Physics Topics
Replies
4
Views
12K
• Engineering and Comp Sci Homework Help
Replies
2
Views
1K
• Electrical Engineering
Replies
81
Views
5K