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Page 15

| mentioned earlier. Since the same magnetic field is responsible for the current induced in the second coil, then the ampere-turns of the second coil must match the ampere-turns of the first coil. In the coils mentioned above, therefore, the current in the first coil will be one tenth that of the second; for instance, the current in the secondary winding (or second coil) will be 10 amperes. |

| Another way to prove the same thing is to measure the power input and compare it to the output. Remembering that power is represented by the product of the voltage and current, then, neglecting losses, |

| All of the above relations may be expressed simply as follows: |

| NP |

| = Number of turns in primary winding. |

| NS |

| = Number of turns in secondary winding. |

| EP |

| = Voltage induced in primary winding. |

| ES |

| = Voltage induced in secondary winding. |

| IP |

| = Current flowing in primary winding. |

| IS |

| = Current flowing in secondary winding. |

| Turns Ratio |

| Whether a transformer is of a step-up or step-down type, the power in the primary is equal to the power in the secondary. Thus, if the load draws 1000 watts, the product of voltage and current in the primary is also equal to 1000 watts. Another important principle is the fact that the primary and secondary voltages are in the same ratio as their turns. If the secondary has twice the turns of the primary, the secondary voltage will be twice as great as that of the primary. Figure 1-16 (on page 16) illustrates the significance of turns ratio. |

| Action of Transformer Under Load.. |

| The transformer also acts automatically to regulate the flow of energy in the primary as it is demanded by the load connected to the secondary. When no circuit is connected to the secondary coil, no current will flow in it. However, a current will flow in the primary coil because it presents a continuous path. This current will set up an alternating magnetic field which will cause a voltage to be self-induced in the primary coil. If there are no losses considered in the transformer, that is, if a perfect transformer is assumed, then the self- |

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