__CHAPTER 7 ALTERNATING CURRENT__

- An alternating voltage
*v*=*v*sin ω_{m}*t*applied to a resistor*R*drives a current*i*=*i*sinω_{m}*t*in the resistor,*i*. The current is in phase with the applied voltage._{m}=v_{m}/R

- For an alternating current i = i
_{m}sin ωt passing through a resistor R, the average power loss P due to joule heating is (1/2) i^{2}_{m}

- The phase relationship between current and voltage in an ac circuit can be shown by representing voltage and current by rotating vectors called phasors.

- A phasor is a vector which rotates about the origin with angular speed ω.

- The magnitude of a phasor represents the amplitude or peak value of the quantity (voltage or current) represented by the phasor.

- Transformer: A transformer consists of an iron core on which are bound a primary coil of N
_{p}turns and a secondary coil of N_{s}

- If the secondary coil has greater turns that the primary, the voltage is stepped up and the transformer is called a step-up transformer.

- If the secondary coil has less number of turns than the primary coil, the voltage is stepped down and the transformer is called a step-down transformer.