Electronics - SS2 Physics Past Questions and Answers - page 2

Resistors are passive electronic components that are used to restrict the flow of electric current in a circuit. They are primarily used to control the voltage and current levels within a circuit and to provide stability. Resistors come in different types, including fixed resistors and variable resistors. Fixed resistors have a constant resistance value, whereas variable resistors (potentiometers) allow the resistance to be adjusted. Resistors affect the flow of current by creating a voltage drop across them, according to Ohm's Law (V = I x R). They dissipate power in the form of heat, and their resistance is measured in ohms (Ω).

Capacitors are electronic components used to store and release electrical charge in a circuit. They consist of two conductive plates separated by a dielectric material. When a voltage is applied across the plates, charge accumulates on each plate, resulting in the storage of electrical energy. Capacitors are used in various applications, such as energy storage, timing circuits, noise filtering, and coupling capacitors. They are commonly employed in power supply circuits to smooth out voltage fluctuations and stabilise the output. Capacitors also play a crucial role in AC circuits, where they can block DC signals and allow the passage of AC signals.

Diodes are semiconductor devices that allow the current to flow in only one direction. They consist of a P-N junction, where the P-type material is positively doped, and the N-type material is negatively doped. Diodes operate based on the principles of forward bias and reverse bias. In forward bias, the positive voltage is applied to the P-side, and the negative voltage is applied to the N-side, allowing current flow. In reverse bias, the positive voltage is applied to the N-side, and the negative voltage is applied to the P-side, preventing current flow. Diodes have various applications, including rectification (converting AC to DC), signal modulation and demodulation, voltage clamping, and protection against reverse current flow.

When a capacitor is connected in an RC circuit to a DC voltage source, it initially acts as an open circuit due to its inability to conduct DC current. As a result, the capacitor begins to charge up gradually. The voltage across the capacitor increases exponentially towards the applied voltage of the source. This charging process follows a time-dependent behaviour known as the exponential charging curve. As time passes, the voltage across the capacitor approaches the value of the applied voltage, and the rate of change decreases until it reaches a steady-state condition.

The time constant in an RC circuit is defined as the product of the resistance (R) and the capacitance (C). It represents the time it takes for the voltage or current to reach approximately 63.2% (1 - 1/e) of its final value during charging or discharging. The time constant is crucial in determining the rate at which the capacitor charges or discharges and influences the behaviour of the circuit. A smaller time constant results in a faster charging or discharging process, while a larger time constant leads to a slower response. The time constant also affects the shape of the voltage or current waveform, with a shorter time constant resulting in a steeper curve and a longer time constant resulting in a more gradual curve.