What is an Ohm and How do Resistors Work?
An ohm (symbol: Ω) is the SI unit of electrical resistance, named after the German physicist Georg Simon Ohm. It represents the resistance in a circuit when a voltage of one volt (V) applied across it generates a current of one ampere (A). In other words, if you have a device with a resistance of 1 ohm, and you apply 1 volt across it, it will allow a current of 1 ampere to flow through it. The relationship between voltage (V), current (I), and resistance (R) is given by Ohm's law, which states:
Resistors are used to control the flow of electric current in circuits. They are designed to have a specific resistance value, which is measured in ohms (Ω). Here's how resistors work:
1. Limiting Current: Resistors limit or regulate the flow of electrical current in a circuit. The higher the resistance, the lower the current flow for a given voltage applied across the resistor.
2. Voltage Division: Resistors are used in voltage divider circuits to create a specific voltage that is a fraction of the input voltage. This is useful for providing different voltage levels from a single source.
3. Heat Dissipation: When electric current flows through a resistor, it converts electrical energy into heat due to the resistance. This property is utilized in applications like electric heaters.
4. Signal Modulation: In electronic circuits, resistors can be used to adjust signal levels, modify bandwidth, or bias active elements like transistors.
5. Time Constants: When used in combination with capacitors or inductors, resistors can influence the charging and discharging time, affecting the behavior of filters, oscillators, and delay circuits.
When measuring resistance across a component or material, a multimeter sends a small (known) current through the component and measures the voltage across it. By using Ohm’s law, the resistance can then be calculated:
The gold band in the example measurement indicates a 5% tolerance. In this case, the nominal resistance of the brown/black/orange/gold resistor is 10kohm +/- 5%.
Resistors work by providing opposition to the flow of electric current. The material of a resistor has atoms that impede the flow of electrons, the carriers of electric current. The degree of opposition depends on the material's resistivity, the resistor's dimensions, and its temperature. The resistance is a fundamental property of the resistor, determining how much it will resist the current flow based on its value (in ohms).
Resistors are manufactured in various forms, such as fixed resistors with predetermined resistance values and variable resistors (potentiometers or rheostats) whose resistance can be adjusted. They are crucial for controlling electrical properties in circuits, ensuring the proper operation of electronic devices.
