Here we have the notes from the central octave.

Although they are written one after another:

line, space, line, space, line, space, etc.

the interval between them is not always the same.

So between C and D, we have an interval of a large second,

or - a whole tone.

Between D and E, similarly we have one tone.

Between E and F, on the other hand,

although they are written consecutively,

we have a semi-tone, meaning - a half of a tone.

Between F and G - tone, G and A - tone,

A and B - tone, and between B and C - semi-tone.

In order for the explanation to be easily visualised,

I have drawn for you the piano keys.

These would be the white piano keys

and these the black ones, as you can see.

This is the key for the C note.

Between C and D there is a whole tone.

Between D and E, a whole tone.

Between E and F, a semi-tone.

And we can visualise this, because we see that the black key is missing.

The same case is between B and C.

Let's write C, D, E, F, G, A, B, C;

ie: Do, Re, Mi Fa, Sol, La, Si, Do

So between E - F and B - C, we have semi-tone.

Let's hear a tone! - between C and D (playing notes on the piano)

between D and E

between E and F it's a semi-tone

How would it sound like if it would be a whole tone?

But it is a semi-tone and it sounds like this

You hear - that this is an dissonant interval,

disturbing to the ear.

And the whole-tone interval is not as disturbing

as the semi-tone would be.

These intervals are also named

large-second and small-second: tone and semi-tone

The semi-tone interval, specifically because it is

so disturbing to the ear, is used for

tunning the car horns, it sound dissonant.