How are analogue and digital signals similar/different?

Why does noise interference affect analogue signals but not digital signals?

• Infrared Signals + Optical Fibre Transmission science homework... =D

• Answer:

  Analogue signals are constantly changing electromagnetic waves which can be influenced by external electromagnetic fields (i.e., "noise"). Digital signals are electrostatic pulses of a fixed amplitude. They resist external fields because the pulses are either fully on or fully off. The noise signals typically have far less power than the digital pulses, so don't affect digital signals. Because analogue signals can vary in intensity, they are more susceptible to small interferences from electronic noise.