Q.Give any two uses of microwaves.

Once a modulated signal is radiated by the transmitting antenna, it must travel through the intervening space to reach the receiving antenna, losing strength steadily as it goes. Wireless communication as a whole spans frequencies from about 2 kHz up to 400 GHz, and depending on where a given signal's frequency falls in this range, it reaches the receiver by one of three physically distinct modes. Ground wave (surface wave) propagation, used for roughly 2 kHz to 2 MHz, is where the wave glides along the Earth's surface, attenuated by increasing distance, absorption of energy by the Earth (which behaves like a leaky capacitor), and the tilting of the wavefront along the Earth's curvature; it underlies local broadcasting, ship-to-shore and short-range mobile communication. Sky wave (ionospheric) propagation, used for roughly 3 MHz to 30 MHz, is where the wave is radiated upward at large angles and bounced back to Earth by the charged, ionised layer of the upper atmosphere (the ionosphere), letting radio signals cover very large distances through multiple successive reflections; the skip zone is the region where neither the ground wave nor the sky wave is received. Space wave propagation, used for roughly 30 MHz to 400 GHz, is where the wave travels essentially in a stra …