Want this question answered?
it usually depends on the type and size; Usually one, sometimes 2; I have played where I'm the only harpist, and other times where it is a harp enselmble or orcchrestra where everybody plays the harp.
String Orchestra songs, Symphony Orchestra songs, and string quartets, not to mention solos.
When used to describe the ensemble, then yes.
it was during the 16th and 17th century
Not really... although the terms are generally used synonomously, these days. An orchestra is defined as an ensemble of different families of instruments. So, that could include concert bands, big bands and the jazz orchestra (big band, 2 horns and strings), among others. A symphony is a specific musical form, usually played by a (fairly) specific ensemble. So, the term "symphony orchestra" is literally an ensemble capable of playing that kind of piece... thus the modern symphony orchestra. Generally, the term "symphony orchestra" is more specific, when talking about the classical ensemble.
Yes, picollo's are used in full-sized orchestras, the London Symphony Orchestra use them in their performances. In fact, every orchestra uses one or more piccolo when the music requires this.
That stick orchestra conductors use is called a baton.
A symphony or an Orchestra. There are also some rock drummers who have placed and used timpanis on their drum sets.
Trumpet
The saxophone is used primarily in jazz/big band and concert wind ensembles. It is not commonly used in a symphony orchestra with the exception of a few saxophone concerto's.
The harp and guitar are both, sometimes used in the orchestra ( the harp more than the guitar ). The instrument known as the "harp-guitar" is a very rare hybrid instrument. Most of its repetoire is in solo pieces and chmber music. It is not a regular member of the symphony orchestra.
The harp isn't used in every composition written for classical music ... a harp part has to exist for it to be used as part of the orchestral ensemble. Sometimes it is used as a solo instrument. Sometimes it is used to add color (ie. glissandi) to a composition. Some composers double the harp part in piano or other instruments.