Class 12 Physics - KERALA
Alternating Current
The 'Alternating Current' chapter in Class 12 Physics for Kerala SCERT students explores electrical currents that periodically reverse direction. You will learn about AC voltage applied to individual circuit elements like resistors, inductors, and capacitors, as well as combinations in LCR circuits. The chapter highlights the phenomenon of resonance, power in AC circuits, and the working principles of crucial devices like transformers and AC generators. This is a high-scoring and conceptually vital chapter for the Kerala Board exams, frequently featuring both numerical problems and derivations.
Start Learning FreeKey Concepts
Alternating Current and Voltage
Current that varies sinusoidally with time, reversing its direction periodically with a standard frequency of 50 Hz in India.
RMS Value of AC
Root Mean Square (RMS) value is the equivalent direct current that would produce the same heating effect in a given resistor over time.
Inductive and Capacitive Reactance
Reactance is the opposition offered by inductors (XL) and capacitors (XC) to the flow of alternating current, measured in ohms.
LCR Series Circuit and Resonance
A circuit containing resistor, inductor, and capacitor where resonance occurs when inductive reactance equals capacitive reactance, resulting in maximum current.
Power in AC Circuits
The average power consumed in an AC circuit depends on the voltage, current, and the cosine of the phase angle, known as the power factor.
Transformer
A static electrical device based on mutual induction used to step up or step down AC voltages with high efficiency.
Important Formulas
Board Exam Info
In the Kerala (SCERT) Class 12 Physics board exam, this chapter typically carries around 6 to 8 marks. Expect direct derivations like the impedance of an LCR series circuit, conceptual questions on power factor, and numerical problems based on resonant frequency and transformers.
Frequently Asked Questions
Why is the average value of AC over a complete cycle zero?
Because the positive half-cycle and negative half-cycle are completely identical in magnitude but opposite in direction, canceling each other out over one full period.
What is the power factor of a purely inductive or purely capacitive circuit?
The power factor is zero because the phase angle between voltage and current is 90 degrees, making cos(90) = 0.
Why do transformers work only on AC and not on DC?
Transformers rely on electromagnetic induction, which requires a changing magnetic flux. DC provides a steady current producing constant magnetic flux, so no induced EMF is generated in the secondary coil.
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