How does a resistance work

Electronic components / passive / resistance

In German, 'resistance' refers to both the simplest electrical component (the resistance) and its property (the resistance value), namely to oppose the electrical current with a resistance. We generally mean the component 'resistance' here. The function of a resistor is to convert the applied energy into heat. If the applied energy (voltage, current, time) becomes too great, the component will be destroyed.

Structure [edit]

There are resistors in mechanical dimensions from very small (SMD) to garage size (load resistance in TV transmitters). The resistance material can be graphite (carbon film resistor), certain metal mixtures (metal film) or resistance wire.

Use [edit]

Resistance [edit]

The resistance value of a resistor is measured in ohms (Ω). 1 Ω is one volt divided by one ampere.

Series resistor [edit]

Used as a series resistor, it limits the current in the circuit and the voltage on neighboring ones[1] Components.

  • Example 1: If you have a voltage source with 9 volts available and want to light up a lamp with 3 volts and 0.5 amps, then you have 6 volts too much. These 6 volts should drop across the resistor. Invoice: . The resistor becomes warm and must be able to give off its warmth. The power of the resistor is calculated as follows: . So you need a resistor with at least 3 watts.

Series connection [edit]

In a series connection, resistors are connected in series so that the same current flows through all components. A voltage drops across the series-connected resistors. A high voltage is dropped at "large" resistors, and a lower voltage at "small" ones. Series connections are used to divide the available voltage. Modern Christmas tree lighting, which is connected to the socket without a ballast, is realized through a series connection of many lamps with a low voltage each, for example 20 lamps connected in series with a voltage of 12 V each.

  • The total resistance of a series connection is the sum of the individual resistances.
  • The voltage drops at the first resistor from. For the second to the last resistance, you do the same calculation.
  • Since the voltage is divided, the same applies to the power.

Parallel connection [edit]

With a parallel connection, the resistors are connected next to each other. The same voltage is applied to all resistors. The larger the individual resistor in a parallel circuit, the lower the current intensity through this resistor. The total resistance of a parallel connection is always smaller than the smallest individual resistance. The household network in an apartment is implemented in parallel. At every socket there are 230V, the amperage of devices can be added.

  • The total resistance is the reciprocal of the sum of all the reciprocal resistance values ​​involved. As a formula:
  • The power of the individual resistors add up to the total power
  • The current through a single resistor is calculated by

Voltage divider [edit]

Resistance in the AC circuit

An ideal resistance shows no special features in an alternating current circuit.


  1. ↑ To be more precise: on components of the same mesh.