Which characteristic of a carrier light wave is modulated for the modulation of a light wave?

Radio waves of constant amplitude are produced by a/an . . . . . . .

$A$ $TV$ transmitting antenna is $128 \ m$ tall. If the receiving antenna is at the ground level,the maximum distance between them for satisfactory communication in line-of-sight mode is (radius of the earth $R_e = 6.4 \times 10^6 \ m$):

If a transmitting antenna of height $105 \,m$ is placed on a hill, then its coverage area is (in $\,km^2$)

In an $AM$ wave,the total power is $900 \ W$. For $100\%$ modulation,the power transmitted in the sidebands is ... $W$.

If the range of a $TV$ telecast is to be doubled,the height of the transmitting antenna must be: