## What does resistance mean?

You have already seen the video on the topic of the research projects of Georg Ohm in class. The next video will give you a short overview on the three electrotechnical basic quantities voltage, current and resistance.

Source: YouTube

**Questions regarding the video:**

- In the video an animation, which illustrates voltage and current, can be seen.

- Which element is equivalent to voltage?
- How has the animation to be changed to improve voltage?
- In what way (and by using which units) is the current represented?

- In the video the word “resistance” is represented in the animation symbolically.

- Which units do represent the resistance?
- How can the resistance be increased or decreased in the animation?

**In which parts of our everyday life does the electrical (Ohm´s) resistance matter?**

In electrical engineering resistance plays an important role. Each element in an electrical circuit (even the wires) have - more or less - a high electrical resistance, which influences the voltage and currents in an electrical circuit. The electrical resistance is also known as ohm´s resistance.

**Effect of electrical resistance**

Source: Electronic Comendium: (https://www.elektronik-kompendium.de/sites/grd/0201112.htm)

You must picture the effect of electrical resistance on electrical current in this way: The movement of free charged carriers on the inside of the conductor results in free charges carriers, which collide with atoms and disrupt the normal behavior of the atoms. This effect is called resistance, which has the ability, to limit the current in an electrical circuit.

**Ohm´s Law**

The Ohm´s Law states that the amperage I in a conductor and the voltage U are between the ends of the conductor directly proportional. The formula U= R*I is a mathematical representation of this law (linear dependence of U and I, the proportional factor is represented by resistance R). By using the Ohm´s Law the three electrotechnical basic quantities can be calculated in an electrical circuit under the premise that two of them are given.

The three basic quantities are voltage, current and resistance. The physicist Georg Simon Ohm identified and proved the connection of voltage, current and resistance. The Ohm´s Law is named after him.

U = R . I

**Overview of the terms and their units**

**Voltage**: Unit 1 V (1 volt), formula symbol U

**Current** (amperage): Unit 1 A (1 ampere), formula symbol I

(electrical or ohm´s) **resistance**: Unit 1 Ω (1 Ohm), formula symbol R