Electrical resistance

Briefly, the most important thing about electrical resistance

Electrical resistance - the property (ability) of the conductor to prevent the passage of electric current. The electrical resistance is denoted mostly by the Latin letter R, the unit of resistance in SI - Ohm.

The nature of the phenomenon, which we call electrical resistance

During their motion, the carriers of electric charges interact with the atoms of the conductor and give off energy. This leads to energy loss by the charge carriers and the amount of current flowing through the conductor decreases. Atoms that are in oscillating motion around the equilibrium position, while increasing the amplitude of oscillation. Thus, the energy of the electric field is converted into the energy of oscillation of atoms, ie heat.

What determines the electrical resistance

The electrical resistance depends on the property of the conductor itself, which is called the resistivity, and is denoted by the letter ρ (simply put, on the number of electrons that can break away from their atoms and become free).

The electrical resistance also depends on the length of the conductor itself : the longer the conductor, the greater the resistance it exerts to the electric current that passes through it.

The electrical resistance also depends on the cross-sectional area of the conductor : the larger this area, the more electrons can pass through the conductor at the same time and, consequently, the lower the resistance.

For a conductor of length L (cm) and cross section S (cm 2 ), the electrical resistance is determined by the formula


where ρ is the resistivity - the resistance of the conductor of cubic shape with unit dimensions. The lowest value of ρ for silver and gold, which is why these materials are used to make contacts in chips.

Electrical resistance is measured in ohms (ohms), kiloohms (kOhms), megohms (mOhms). 1 ohm is approximately the resistance of a 62-meter-long copper wire with a cross-sectional area of 1 mm 2 .

A small animation shows the influence of the above factors on the resistance of the conductor:


An example of the use of electrical resistance

The following is a very, very simple electrical circuit: the power supply is a battery, a circuit breaker (connector), and two wires that connect the "+" and "-" power supplies to the circuit breaker. As soon as the circuit breaker contacts are connected, current will begin to flow around the circuit, thin conductors have very little resistance to the passage of current, and the battery will discharge quickly.

Electrical-resistance-2     Electrical-resistance-2-1     Electrical-resistance-2-3

Below is the same simple electrical circuit, but it already has a light bulb. As soon as the circuit breaker contacts are connected, current begins to flow through the circuit, the thin conductors have very little resistance to the passage of current, but now the circuit has an incandescent light bulb made of tungsten, a conductor that has a very strong electrical resistance.


The temperature of the tungsten filament rises sharply after the current is turned on. The filament begins to emit electromagnetic waves (and we remember that light is electromagnetic waves). To obtain visible radiation, it is necessary that the temperature be of the order of several thousand degrees (usually 2300 - 2900 ° C), ideally 6000 ° C (surface temperature of the Sun). The lower the temperature, the smaller the proportion of visible light and the more "red" this radiation becomes.

The incandescent lamp converts part of the consumed electric energy into radiation, the other part into heat. Only a small fraction of radiation lies in the region of visible light, the main share is infrared radiation.

All this is due to the property of the conductor to resist the electric current and the mind of man, who was able to use this property for their own needs.

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