Trumpet and French horn are both part of the brass instruments family and are widely used by musicians all over the world. Even though they belong to the same family of musical instruments, trumpet and French horn have certain dissimilarities.
The major difference between both the instruments that the French horn is mainly used in orchestras and the trumpet is used in both the orchestras, as well as at bands.
Another major difference is highlighted in the shapes of tubes used in them. In а trumpet, you will find the tubes bent twice into an oblong shape, whereas, the tube in а French horn can be found coiled into а circular shape and coming out to the base of the horn, more or less in the shape of а bell.
In a French horn, you will find a funnel shaped mouthpiece, whereas, a cup shaped mouthpiece is used in trumpets.
Difference in sizes is another parametre that separates both the instruments. The size of the French horns is considerably larger than that of trumpets. That is the reason why its pitch is usually lower than that of trumpets. When it comes to the size of the mouthpieces, French horns sport smaller mouthpieces compared to those installed in trumpets.
Talking about changing the notes in both the instruments, you will find similarities, as you can change the notes by altering the three valves installed on the instruments, as well as by changing the lip tension.
Both the instruments also have different histories. Trumpets have been part of different rituals around the world since ancient times. Before the 19th century, trumpets used to come without valves installed in them. On the other hand, French horns only recently became a part of the brass family of instruments. They were first developed during 1650s in France, and the valves were then added to them during the 19th century.