Home » Free Class Notes for CBSE Board » Class 12 Notes » Class 12 Physics Notes » CBSE Class 12th Physics Notes for Chapter 7 Alternating Current

# CBSE Class 12th Physics Notes for Chapter 7 Alternating Current

CHAPTER 7 ALTERNATING CURRENT

• An alternating voltage v = vm sin ωt applied to a resistor R drives a current i = im sinωt in the resistor, im=vm/R . The current is in phase with the applied voltage.

• For an alternating current i = im sin ωt passing through a resistor R, the average power loss P due to joule heating is (1/2) i2m

• 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 Np turns and a secondary coil of Ns

• 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.