| Directions : (46-50) |
| Transformer |
| A transformer is an electrical device which is used for changing the a.c. voltages. It is based on the phenomenon of mutual induction i.e., whenever the amount of magnetic flux linked with a coil changes, an e.m.f. is induced in the neighbouring coil. For an ideal transformer, the resistances of the primary and secondary windings are negligible. |
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| In can be shown that \[\frac{{{E}_{s}}}{{{E}_{p}}}=\frac{{{I}_{p}}}{{{I}_{s}}}=\frac{{{n}_{s}}}{{{n}_{p}}}=k\] |
| where the symbols have their standard meanings For a step up transformer, \[{{n}_{s}}>{{n}_{p}};\,{{E}_{s}}>{{E}_{p}}\,;\,k>1\,;\,\] |
| \[\therefore \,\,\,{{I}_{s}}<{{I}_{p}}\] |
| For a step down transformer, \[{{n}_{s}}<{{n}_{p}};\,{{E}_{s}}<{{E}_{p}};\,k<1\] |
| The above relations are on the assumptions that efficiency of transformer is 100%. |
| Infact, efficiency \[\eta =\frac{output\,power}{input\,power}=\frac{{{E}_{s}}\,{{I}_{s}}}{{{E}_{p}}\,{{I}_{p}}}\] |
A) Current
B) Voltage
C) Power
D) All of these.
Correct Answer: C
Solution :
In an ideal transformer, there is no power loss. The efficiency of an ideal transformer is \[\eta =1\] (i.e. 100%) i.e. input power = output power.
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