Ohm Law

A resistor operates by resisting or limiting the flow of electrical current through the resistor, given a voltage difference between the two terminals of the resistor. The relation between voltage, electrical current, and resistance can be described by Ohm’s Law.

Ohm's Law, formulated by Georg Simon Ohm in the early 19th century, is one of the basic principles in electronics. It states that the current (I) flowing through a conductor between two points is directly proportional to the voltage (V) across those two points, and inversely proportional to the resistance (R) of the conductor. Mathematically, Ohm's Law can be expressed as:

V = I ⋅ R

• Voltage (V) - measured in volts (V), represents the electrical potential difference between two points in a circuit. It is the driving force that propels electric charge through a conductor.
• Current (I) - measured in amperes (A), is the flow of electric charge through a conductor. Ohm's Law states that the current is directly proportional to the voltage, meaning an increase in voltage results in a proportional increase in current, assuming resistance remains constant.
• Resistance (R) - measured in ohms (Ω), is the opposition that a material offers to the flow of electric current. As per Ohm's Law, if the voltage across a resistor is constant, increasing the resistance will decrease the current flow, and vice versa.
• Power (P) - measured in watts (W), represents the rate at which energy is transferred in a circuit

Sourced from: https://media.digikey.com/pdf/Innovation%20Handbook/Formulas-Laws-and-Equations.pdf

DigiKey has free calculators for many essential electronics calculations including for Ohm's Law.

Resistor Attributes

• Resistance – measured in the unit of Ohms, impedes or regulates the flow of current.
• Tolerance - amount of variation either above or below the stated resistance value.
• Power - maximum steady state power dissipation under specified test condition measured in Watts.

Resistor Types

Surface Mount

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Surface Mount resistors are the small brick like resistor components that are either attached by solder connection or adhesive application to the surface of a printed circuit board. Due to the small size and lack of external leads, humans typically don’t work with surface mount components, but it can be a fun challenge to try: https://www.digikey.com/en/products/detail/chip-quik-inc/SMDPST120/15195098 

Through Hole

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Through Hole resistors are resistor components with wire lead termination designed to be fitted and soldered in place on a circuit board. While the larger size makes through hole resistors easier to work for humans, the larger body also takes up more space on a circuit board making placement difficult at times. The wire leads and nature of soldering makes through hole components more difficult for automated assembly machines.

Chassis Mount

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Chassis Mount resistors are the larger standalone resistor components that are fixed to the chassis or enclosure of the device and are not found on a circuit board. Chassis mount resistors typically have much higher power dissipation than resistors that reside on a circuit board.

Resistor Network

Resistor Networks are multiple interconnected resistors inside the same package. Resistor networks include resistors in series (where all resistors are connected end to end in a line) and/or in parallel (where resistors are connected side by side).

Potentiometers, Variable Resistors

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Potentiometers, often referred to as "pots" are three terminal passive resistors-based devices that can vary the amount of resistance. The most common method a potentiometer can vary the output resistance by physically moving a wiper arm across a length of resistive material, the longer the distance from the input terminal the higher the resistance.

Ceramic

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The most common type of capacitor manufactured today. Ceramic capacitors are made up of one or more stacked layers of ceramic material acting as the dielectric and metal layers as the electrodes. One of the cheapest types of capacitors (per unit) and are found in most consumer electronics today, with applications from power filtering to signal conditioning.

Film

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As the name suggests Film Capacitors are made from layers of plastic film stacked on top of one another with layers of metallic foil or other plastic film with metal applied directly to one side. Due to the plastic film construction, they have higher voltage ratings, lower series resistance, and good stability over temperature ranges.

Aluminum Electrolytic

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Aluminum Electrolytic capacitors, also called aluminum capacitors are some of the most common electrolytic capacitors. They have high capacitance value, small package size, and higher cost (per unit). However, due to poor electrical properties of high ESR, low operating temperature range, and short service life measured in Aluminum capacitors are often used in bulk applications where accuracy is not necessary.

Tantalum

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The name comes from Tantalum being used in the electrode. The electrolyte in a tantalum is (usually) a solid material rather than a fluid as in the case of aluminum capacitors. This allows for a much greater energy storage density with a reduced component footprint and longer service lifespan then aluminum capacitors.

Electric Double Layer Capacitors (EDLC), Supercapacitors

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The latest developments in capacitor materials have led to devices with capacitance values measured in whole units of Farads instead of millionths or billionths of farads. Super capacitors can be thought of as the middle ground between regular capacitors and rechargeable batteries offering quick discharge rates.

Core Types

For the cores of inductors there are two main types, magnetic cores, those made up of iron or ferrite materials, and non-magnetic cores, those that are made up of ceramic, plastic, polymer, or air cores that do not affect the magnetic field generated by the energized coil.

• Magnetic cores – are built around or have the central area filled with a material that has high magnetic permeability such as iron or ferrite compounds. These high magnetic permeability materials can dramatically increase the magnetic field density of a given part making small inductors have greater values then an equivalent nonmagnetic core type. These are used in higher value inductors (those over 1 uH).
• Non-magnetic cores - do not affect a magnetic ­field in which they are placed. When used as inductor cores, they primarily provide mechanical support for the windings rather than participating in the device’s magnetic circuit. Lack of a magnetic core material restricts the amount of inductance that can be achieved in each physical space but avoids core losses and saturation, so devices based on nonmagnetic core materials are mostly low inductance (<1uH) devices with comparably good Q factors, high-frequency performance, linearity, and stability. They commonly are used in RF and signal applications where minimizing non-ideal behaviors is of more importance than the ability to store large amounts of energy.

Inductor types

Wirewound

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As the name suggests, wire wound inductors are simply wire wound around a central core shape.

Molded

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Molded inductors have the core material shaped and formed around the wire wound core.

Multilayer

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Multilayer inductors are constructed somewhat like multilayer capacitors with layers of conductive and insulating materials are stacked.