Class 12 Physics - Alternating Current (AC)

Introduction

• New Chapter: Alternating Current (AC)
• This chapter is interesting and simple if read in the correct sequence.
• Today's lecture is the first lecture on AC.

Main Points

• Difference between Alternating Current (AC) and Direct Current (DC).
• What is meant by the average value of current and EMF?
• What is RMS value?
• Methods to find RMS value.
• Short trick to find RMS value.

Direct Current (DC)

• Direct Current: Flows in one direction.
• DC Symbol: Battery.
• In DC, the current does not change its direction.
• For DC, current flows in a fixed direction.

Alternating Current (AC)

• AC: Changes direction.
• AC current varies with time.

Average Value

• Average Value = ( I_{average} = \frac{1}{T} \int_{0}^{T} I(t) dt )
• Method to find the average value of AC.
• Generally, it is not ( 2I_0 / \pi ).

RMS Value (Root Mean Square)

• RMS Value = ( I_{RMS} = \sqrt{ \frac{1}{T} \int_{0}^{T} [I(t)]^2 dt} )
• Condition for RMS value: ( I_{RMS} = \frac{I_0}{\sqrt{2}} )

AC Generator

• AC is generated through an AC generator.
• ( V = V_0 \sin(\omega t) )

Behavior of Different Elements with AC

• Behavior of resistor, capacitor, and inductor with AC.

Graphs and Average Value

• Explanation of average value in graphs.
• Average current in a complete cycle = 0.
• Average current in a half cycle is ( 2I_0 / \pi ).

Importance of RMS

• The RMS value of electricity in homes is 220V.
• Relationship between RMS and average value.
• RMS value is important in electrical devices.

Solution to Problems

• Methods to find RMS value in different situations.
  • Find the RMS value of ( I = I_0 + I_0 \sin(\omega t) ).
  • Find the RMS value of ( I = I_1 \sin(\omega t) + I_2 \cos(\omega t) ).

Conclusion

• Further material will be discussed in the next class.
• Behavior of resistors and other elements with AC.
• Best wishes to all!