10. Alternating Currents A.md

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Characteristics of Alternating Currents

Dictation/Definition: Define the terms "period," "frequency," and "peak value" as they apply to an alternating current or voltage. Point out these Physics Quantity on a sinusoidal wave graph. Answer:

Period (T): The time taken for one complete cycle of an alternating current or voltage.

Frequency (f): The number of cycles of an alternating current or voltage that occur per unit time, typically measured in Hertz (Hz).

Peak Value (X₀): The maximum value (positive or negative) reached by an alternating current or voltage in one cycle.

Application: Explain how the equation represents a sinusoidally alternating current or voltage. Answer: The equation models a sinusoidal wave, where is the peak value, is the angular frequency (related to the frequency by ), and is the time. This equation describes how the current or voltage changes over time in a sinusoidal pattern, oscillating between the peak positive and negative values.

Formula Recall: State the relationship between the mean power and the maximum power in a resistive load for a sinusoidal alternating current. Answer: The mean power in a resistive load for a sinusoidal alternating current is half the maximum power.

Conceptual Understanding: Distinguish between root-mean-square (r.m.s.) values and peak values. Provide the formulas for calculating the r.m.s. current and voltage for a sinusoidal alternating current. Answer:

Peak Values: The maximum values (positive or negative) an alternating current or voltage reaches.

Root-Mean-Square (r.m.s.) Values: The effective value of an alternating current or voltage, equivalent to the value of a direct current or voltage that would produce the same power in a resistive load.

Rectification and Smoothing

Graphical Distinction: Distinguish graphically between half-wave and full-wave rectification. Answer:

Half-Wave Rectification: Only one half (either positive or negative) of the AC waveform is passed, while the other half is blocked.

Full-Wave Rectification: Both halves of the AC waveform are passed, but one half is inverted, resulting in a waveform that is entirely above or below the baseline without changing polarity.

Explanation: Explain how a single diode is used for half-wave rectification of an alternating current. Answer: A single diode in a circuit allows current to flow through it in only one direction. During half-wave rectification, the diode conducts during one half of the AC cycle (either positive or negative), allowing current to pass, and blocks current during the other half, resulting in a waveform that has current in only one direction.

Full-Wave Rectification: Describe the use of four diodes in a bridge rectifier configuration for full-wave rectification of an alternating current. Answer: In a bridge rectifier, four diodes are arranged in a closed loop ("bridge") configuration to allow both halves of the AC input to be passed through the load. Two diodes conduct in one half-cycle, and the other two conduct in the other half-cycle, inverting one half so that the output is a full-wave rectified waveform.

Smoothing Analysis: Analyse the effect of a single capacitor in smoothing the output of a rectified current, including how capacitance and load resistance values affect the smoothing. Answer: A single capacitor connected across the output of a rectifier circuit acts as a reservoir, storing charge during the peaks of the waveform and releasing it during the troughs. This smoothing effect reduces the ripple in the output. A larger capacitance provides better smoothing due to its higher charge storage capacity, while a higher load resistance allows the capacitor to discharge more slowly, also improving smoothing.