what is modulation ?explain the amplitude modulation with the help of necessary diagram.what is meant by modulation index and the lower and upper side bands?

Modulation is a process of mixing a signal with a sinusoid to produce a new signal. This new signal, conceivably, will have certain benefits over an un-modulated signal, especially during transmission.

Amplitude modulation is a type of modulation where the amplitude of the carrier signal is modulated (changed) in proportion to the message signal while the frequency and phase are kept constant.

Modulation index indicates how much the carrier's amplitude can change due to modulation.

Amplitude modulation of a carrier wave normally results in two mirror-image sidebands. The signal having higher frequency than carrier wave frequency is upper side band and signal having low frequency than carrier frequency is lower side band.