Chapter 35, Problem 1Q

Radio waves and light are both electromagnetic waves. Why can a radio receive a signal behind a hill when we cannot see the transmitting antenna?

To determine

Explain the reason for the radio is receiving the signal behind the hill but one cannot see the transmitting antenna.

Answer to Problem 1Q

The size (wavelength) of the radio waves and hill is comparable so, wave is diffracted from the hill and radio receives signals while the size (wavelength) of the visible waves and hill is not comparable so it could not be diffracted and we cannot see antenna.

Explanation of Solution

Electromagnetic waves are the waves consisting of oscillating electric and magnetic fields. There is a electromagnetic spectra consisting of electyromagnetic waves of different wavelengths. Radio and visible waves are one of them.

Radio waves have  wavelength ranges from $1\text{mm-100}\text{km}$ whereas the visible light waves have wavelength range from $380\text{nm-740}\text{nm}$. Radio waves can diffract through normal sized objects such as hills because of its large wavelength but visible light cannot diffract through the hills due to shorter wavelength.

The slight bending of light from the edge of the object is known as ‘Diffraction’. The light would be diffracted only when the size of the object and the light are comparable to each other.

Conclusion:

Thus, the size (wavelength) of the radio waves and hill is comparable so, wave is diffracted from the hill and radio receives signals while the size (wavelength) of the visible waves and hill is not comparable so it could not be diffracted and we cannot see antenna.