elaborate...... which signal? whats te use of transistor?

More xplanation please!!!

Ua my woofer m her amplifier fier

An amplifier is a device.. usually electronic, that magnifies information to a more powerful signal at the amplifier's output. Amplifiers are usually based on electronic principles but may utilize hydraulics or magnetics.

Amplifiers are used when the electrical power of a signal must be increased. Audio amplifiers can increase the microwatts developed by a microphone to more than a million watts of power required to fill a stadium during a concert. Satellites use amplifiers to strengthen television & telephone signals so they can be received easily when beamed back to Earth.

u r right....