spidey said:so in transformer if we step up voltage,current is reduced and if we step down, current is increased based on p=vi...but based on ohm's law v=ir..so we step up,current should be increasing and and if we step down, current is decreasing right ..which formula is correct?
berkeman said:The open-circuit output voltage of a transformer depends on the turns ratio and the source voltage amplitude. The output current is zero in the open-circuit case.
Once you add a load resistance to the secondary of the transformer, then things change. You need to account for the source impedance and the current in the load resistance, before you can say what the current is. If the transformer were lossless, and the source impedance negligible, then yes, the secondary current is Np/Ns multiplied by the primary current (since there is no power loss in the ideal transformer). But when there are transformer losses, and when the source impedance of the driving voltage source is not negligible, then the output current is less than the ideal value.
V=IR will always hold for the secondary side, but the voltage that you are getting will be pulled down from the source's open-circuit voltage level, due to the drop across the source impedance and due to transformer losses (like voltage drop across the winding resistances).
Does that help?
http://en.wikipedia.org/wiki/Transformer
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Transformers are devices used to transfer electrical energy from one circuit to another, typically by changing the voltage level. They consist of two or more coils of wire wrapped around an iron core. When an alternating current (AC) flows through the primary coil, it creates a changing magnetic field that induces a voltage in the secondary coil, allowing for the transfer of energy.
Step-up transformers increase the voltage level, while step-down transformers decrease the voltage level. This is achieved by varying the number of turns in the primary and secondary coils. Step-up transformers are used to increase the voltage for long-distance transmission, while step-down transformers are used to decrease the voltage for safe use in homes and businesses.
The voltage ratio in a transformer is determined by the ratio of the number of turns in the primary and secondary coils. For example, a transformer with 100 turns in the primary coil and 200 turns in the secondary coil will have a voltage ratio of 1:2, meaning the output voltage will be twice the input voltage.
Yes, transformers are designed to work with AC current. This is because AC current is necessary for creating a changing magnetic field, which is essential for the operation of a transformer. However, devices called rectifiers can convert AC current to DC current, which can then be used in devices that require DC power.
Transformers have a wide range of applications, including power distribution, voltage regulation, and electrical isolation. They are commonly used in household appliances, power grids, and electronic devices. They are also used in industries such as manufacturing and transportation for various purposes, such as powering machinery and controlling power flow.