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.