Question

How do you explain the relationship between voltage and current?

I take Science in french and the question on my sheet is "Écrire la relation entre tension et intensité", so a french explanation would be good.

Answer 1

I'm afraid I am not familiar with French.

But, let me proceed anyway.

Explanation:

The relationship between current and Voltage depends on the material in question.

You see, when you apply a particular voltage between two points in a particular object, a current flows in it (I'm assuming the object is either a conductor or a semiconductor).

The more you increase the magnitude of the voltage, the current increases.

For many substances which are conducting, at a constant temperature,

`V=IR`

This is known as Ohm's law after it's discoverer.

But, let me warn you that there are so many materials and devices around us that don't follow the very simple Ohm's law. (This is a Linear relationship)

For a semiconductor diode, the current voltage relationship is as follows.

`I = I_s[exp(eV/(etakT) - 1)]`

Where `e` charge on an electron. `eta` is a constant depending on the material of the diode,while `k` is the Boltzmann constant and `T` is the absolute temperature.

There are other semiconductor devices like BJTs, FETs, UJTs and MOSFETs in which the relationship between current and voltage cannot be expressed in a simple mathematical form.

For such devices, the analysis is done using graphical methods or by suitable approximate replacements using linear circuits (that obey Ohm's law).

In case of space charge, space-charge limited current (SCLC) in a plane-parallel vacuum diode varies directly as the three-halves power of the anode voltage `V_a`.

That is, `I_a` is proportional to `(V_a)^(3/2)`

This is called the Langmuir Child law.