The relationship among the three fundamental electrical quantities: current, voltage, and resistance was discovered by Georg Simon Ohm (1825–1826).
Ohm's law formula states that, at a constant temperature, the current through a conductor between two points is directly proportional to the electric potential difference across between these two points.

• the electric current

• at the ends of the resistor there is an electrical voltage

• the resistor has an electrical resistance

According to Ohm's law, we have the following simple mathematical equation:

It can be easy seen that doubling the voltage doubles the current that passes through the resistor. Simply, Ohm's law graph is a straight line.

Above you can see the voltage and current plot for the two linear resistances. If the current is on the y-axis and the voltage on the x-axis, the slope of the line is equal to 1/R. Thus, the smaller the slope, the greater the resistance of the used resistor.

There is a lot of Internet sources where you can find detailed considerations on this subject - e.g. look here.
You will also find plenty of so-called Ohm's law calculators and simulations on the internet. Here you have simulations of physical phenomena with description in many European languages, and of course Ohm's law is also there (English, Polish).

Note that Ohm's law only applies to electrical conductors. However, there are also materials with other electrical properties (semiconductors, insulators). These materials don't have a straight line plot for voltage and current. All materials with a linear I(U) diagram obey Ohm's law and are therefore called ohmic conductors.

You already know what Ohm's law is, so it's time to experiment. Try to verify the Ohm's formula in practice ( I = U/R ).

**How experiment can be done? Use our online laboratory for this**.

To download the resistor for the experiment, you must have the code of the corresponding drawer in my virtual warehouse. I give out the codes in class. If you are not my student, you can use the universal code available to everyone (900909090).

Take appropriate current and voltage measurements and then do a graph of the current through the resistor versus the voltage across the resistor. We expect it to be a straight line.

Everything is perfect in **simulations** and in theory - all measuring points lie on the line *I(U)*.

For example, if you use a resistor with a resistance of 10 kohms (10 thousand ohms) and apply a voltage of 10V to its ends, you will get a current value of exactly 1mA (mA = one thousandth of an ampere A). In real experiments (also in our online lab) we use meters that have a finite accuracy. Moreover, these meters have certain resistances. This aspect can be well analyzed when discussing Kirchhoff's laws. To sum up, we should not be surprised that the measuring points are not perfectly on a straight line.

So, construct a graph:. draw perpendicular I and U axes. Markt the appropriate scales on the axes and mark your measurement points. Draw the best-fit line to these measurement points (I recommend you to use the least squares method). The slope of this line is equal to 1/R because U = I/R.

You can perform these experiments for two variants of measuring circuits with the same resistor. If you obtain different resistance values R, try to analyze out why.

Good luck :)