Class 12 Physics - BIHAR
Alternating Current
The 'Alternating Current' chapter for Class 12 Physics under the Bihar Board (BSEB) explores electrical currents that reverse direction periodically. You will study fundamental concepts such as peak and RMS values of alternating current and voltage, phase relationships between voltage and current in resistors, inductors, and capacitors (R, L, C circuits), and the phenomenon of electrical resonance in LCR series circuits. The chapter also covers power in AC circuits, the power factor, and essential devices like transformers and AC generators. This is a high-scoring and crucial chapter for the BSEB physics board exams, frequently featuring both numerical problems and theoretical derivations.
Start Learning FreeKey Concepts
Alternating Current and Voltage
An electric current whose magnitude changes continuously and direction reverses periodically with time, typically represented by a sinusoidal wave function.
Root Mean Square (RMS) Value
The effective value of AC, defined as that steady current which would produce the same amount of heat in a given resistor in a given time as the AC does.
Reactance and Impedance
Reactance is the opposition offered by an inductor (inductive reactance) or a capacitor (capacitive reactance) to AC, while impedance is the total opposition offered by an LCR circuit.
Electrical Resonance
A condition in a series LCR circuit where inductive reactance equals capacitive reactance, resulting in maximum current and minimum impedance at a specific resonant frequency.
Power in AC Circuits and Power Factor
The average power dissipated in an AC circuit depends not only on voltage and current but also on the cosine of the phase angle between them, known as the power factor.
Transformer
A static electrical device based on mutual induction used to step up or step down alternating voltages with high efficiency.
Important Formulas
Board Exam Info
In the Bihar Board (BSEB) Class 12 Physics examination, the Alternating Current chapter typically carries around 5 to 7 marks. Questions usually include objective (MCQs), short-answer conceptual questions (such as defining RMS value or power factor), and long-answer derivations or numerical problems related to series LCR circuits and transformers.
Frequently Asked Questions
What is the difference between direct current (DC) and alternating current (AC)?
Direct current flows in only one constant direction, whereas alternating current periodically reverses its direction and changes its magnitude continuously with time.
Why can a transformer not be used with direct current (DC)?
A transformer works on the principle of electromagnetic induction, which requires a changing magnetic flux. Since DC produces a constant magnetic field, it cannot induce a current in the secondary coil of a transformer.
What is meant by a power factor of zero?
A power factor of zero occurs in a purely inductive or purely capacitive AC circuit, meaning the phase angle between voltage and current is 90 degrees and no power is consumed in the circuit.
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