May. 13, 2024
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Here's a physics-based introduction to the electrical engineering concepts you're trying to understand.
Your questions are answered at the bottom.
The study of electronics revolves around understanding how electrons move through a system. Electrons, which carry a negative charge, are the primary charge carriers in most circuits. The charge of an electron is \(-1.602{\times}{10}^{-19}\) Coulombs. Conversely, protons carry a positive charge of \(+1.602{\times}{10}^{-19}\) Coulombs, but they are much harder to move due to the nuclear strong force binding them to neutrons in atomic nuclei.
Electrons, on the other hand, can be easily dislodged from their atoms, a principle that is fundamental to the operation of solar cells through the photoelectric effect.
Charges create electric fields that extend indefinitely through space. These fields can be visualized as vectors pointing toward the charge, governed by Coulomb's Law:
$$\lvert \vec E\rvert = \frac{1}{4\pi\epsilon_{0}} \frac{\lvert q\rvert}{r^{2}}$$
This equation indicates that the force exerted by an electric field decreases with the square of the distance from the source charge.
The total electric field at any point is the vector sum of the fields created by all individual charges present. This superposition principle applies to calculations involving multiple charges, similar to solving kinematics problems with multiple forces acting on an object.
In electronic circuits, positive charge usually denotes an absence of electrons, while negative charge indicates a surplus. Electrons move in response to electric fields, creating current flow. The macroscopic behavior of electrons can be predicted despite their individual random trajectories due to quantum mechanics and Brownian motion.
Electric potential measures the work needed to move a positive test charge from infinitely far away to a given point in an electric field. Analogous to gravitational potential, electric potential affects how charges move within the field:
In conductive materials, applying an electric field causes free electrons to move, creating a potential difference (voltage) along the conductor. This results in an equilibrium charge distribution where the net movement of electrons is zero.
A typical galvanic cell uses a redox reaction to generate electric fields, causing electron flow. Eventually, ion buildup prevents further reaction, making the power source non-ideal. Ideal power sources, in contrast, maintain consistent electric field strength.
Consider an ideal voltage source as a magical escalator that continually moves tennis balls (electrons) back to the top of a hill (high potential). Just as the escalator ensures a continuous flow, an ideal voltage source maintains a consistent electric potential difference.
Electrical current, defined as the flow of charge per second through a cross-sectional area, depends on charge density and conductor properties. It's the rate at which charge carriers (electrons) pass through a given point.
The principle of charge conservation ensures that charge is neither created nor destroyed in a circuit. Similarly, voltage sources generate electric potential but do not create charge, maintaining the overall balance of charge and potential in the system.
Kirchhoff's Current Law indicates that the total current entering a node equals the total current leaving the node. The distribution of current depends on the resistance of various branches in the circuit, analogous to water flow in river systems.
All charge entering a node must exit the node. In a single series circuit, current remains constant throughout as per the conservation of charge. Different amounts of current can flow through parallel branches based on their resistance.
LEDs and resistors don't "use" current, as charge remains the same throughout a series circuit. The current flow is influenced by the LED and resistor characteristics described by their i-v curves.
LEDs have an activation voltage typically around 1.8 to 3.3 V. Below this threshold, current flow is minimal. LEDs emit light at specific wavelengths based on their energy levels, highlighting their efficiency compared to other light sources.
Kirchhoff's Voltage Law states that the sum of voltage drops around a circuit loop is zero. In a series circuit, voltage drops across each component until fully utilized.
Resistor selection depends on the LED's current rating and Ohm's law. The voltage will be fully utilized while current remains constant in a series circuit.
Directly connecting battery terminals causes a large current flow, dissipated as heat due to internal and conductor resistance. This can overheat and damage the battery.
Resistors regulate current flow, preventing excessive current that could damage components like LEDs. They ensure the longevity and proper functioning of the circuit.
Resistors are fundamental components in electrical circuits, found in nearly every device. They divide voltages, limit current, and protect sensitive parts.
If you browse the RS Components catalogue, you'll find a vast array of resistor types. They mainly fall into fixed and variable categories, each serving different purposes in various applications:
Carbon composition resistors mix carbon granules with glue to limit current, though they've mostly been replaced by carbon film resistors, which offer better longevity and thermal consistency.
These resistors boast high precision with tolerances as low as 1%, making them suitable for applications requiring precise voltage control, such as sensitive measuring devices.
Wire-wound resistors handle high currents by using wound wire materials with higher resistance. They are used in DC and low-frequency applications where inductance isn't an issue.
Variable resistors allow for precise circuit calibration. These resistors function by adjusting the length of the resistive material, thereby varying the resistance.
Potentiometers connect different voltage points and adjust the output voltage through a movable contact or wiper. They are commonly used in audio applications to control signal amplitude.
Rheostats adjust resistance by effectively shorting parts of the resistive material from the circuit. They're used in devices like dimmer switches where current needs fine-tuning.
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