Passive Components
Passive components are electronic components that do not require any form of electrical power to operate. As these devices are passive, they do not provide gain, amplification, or directionality to a circuit, instead of that they result in attenuation (in this case, the reduction of an electric current also used to refer to the reduction in the magnitude of a radio signal or any other oscillation). Passive components do not generate energy but can store it or dissipate it.
Passive devices can be used individually or connected together within a circuit, either in a series or in a parallel combination to control complex circuits or signals, produce a phase shift to the signal, or to provide some form of feedback, but they can not multiply a signal by more than one as they have no power gain. Passive devices are bi-directional components, which is why they can be connected either way around within a circuit unless they have a specific polarity marking, such as electrolytic capacitors. The polarity of the voltage across them is determined by conventional current flow from the positive to the negative terminal. Examples of passive components include resistors, capacitors, diodes, inductors, and transformers.
Resistors
A resistor is an electronic component that resists the flow of electrical current. It is a passive device used to control, or impede the flow of electric current in an electric circuit by providing resistance, thereby creating a drop in voltage across the component. The resistor is the most widely used component in electronic circuits.
While the appliances and devices connected in a circuit also offer resistance to the flow of current; however, sometimes their resistance is not enough to reduce the current flow sufficiently for the voltage applied to the circuit. For example, if a light bulb does not offer sufficient resistance, more current than is necessary will flow through the bulb, causing it to burn brighter and reducing its lifespan as it will burn out faster than it should. In addition to a measured resistance to the circuit in the form of a resistor, the component will reduce the current flow to an optimal value. Components known as variable resistors can also be used to allow the resistance to be increased or decreased by external control, causing the light bulb to burn brighter or dimmer, as required.
The value of a resistor is measured in ohms and represented by the Greek letter capital omega (Ω). Resistors usually have a brown cylindrical body with a wire lead on each end and colored bands that indicate the value of the resistor. Resistor values range from as low as 1 ohm to 9 megaohms.
Capacitors
Capacitors are components that store small amounts of electrical energy when a current is passed through it. Capacitors contain two electrical conductors, often in the form of metallic plates separated by a dielectric medium. A dielectric medium is very similar to an insulator, in which it does not allow current to pass through, but there is one difference. In dielectric materials, electric polarization occurs when a voltage is applied across it, and a current flows through it. Polarization occurs when positive charges are pulled to one side and negative ones to the other side. This separation of charges results in a build-up of energy in the capacitor.
The separation is maintained while the current is flowing. The current may stop the charges from moving towards each other due to the force of attraction, and the energy will be released in the form of a current.
Materials commonly used as dielectrics include glass, ceramic, plastic film, paper, and mica. The effect of a capacitor is known as capacitance. The unit of measurement for capacitance is Farad, but this unit is much too large for practical work. It is usually measured in microfarads (μF) or picofarads (pF). The ability of capacitors to store energy is useful in electronic devices in many ways. One of the main uses of a capacitor is to ensure a steady DC voltage is applied across a circuit or a component. These are referred to as decoupling capacitors and act as a very small and local power supply for components. If the power supply drops very temporarily, its voltage a decoupling capacitor can briefly supply power at the correct voltage. The circuit or the component is then shielded from these voltage fluctuations, thus allowing the circuit to function with interruption and protecting its components.
Capacitors are connected between the power supply and ground, in parallel with the component. While this appears as a short circuit connection between power and ground, capacitors only allow high-frequency signals to pass through the DC signal will go to the component as required. They also serve to clean the supply of unwanted noise.
In some applications, like the flash of a camera, you need a sudden release of energy to power the flashbulb. It is precisely what a capacitor does. The capacitor is charged by the power supplied from the batteries, in the camera, and it holds its charge. When you press the button on the camera to take a picture, the circuit between the capacitor and a flashbulb is closed, which causes the energy from the capacitor to be released in a burst and that lights up the flashbulb for the brief time required or a flash.