Which device is used to convert one form of energy into another?

The carrier frequency of a transmitter is provided by a tank circuit of a coil of inductance $49\,\mu H$ and a capacitance of $2.5\,nF$. It is modulated by an audio signal of $12\,kHz$. The frequency range occupied by the side bands is

$A$ carrier wave of peak voltage $15 \,V$ is used to transmit a message signal. If the modulation index is $60 \%$, then the peak voltage of the modulating signal is (in $\,V$)

In an $AM$ wave,the frequencies of $LSB$ and $USB$ are $2.99 \ MHz$ and $3.01 \ MHz$ respectively. The carrier frequency is ....... and the modulating frequency is .......

The height of a transmitting antenna is $h \ m$ and the height of a receiving antenna is $45 \ m$. The distance between them is $40 \ km$. For satisfactory $Line\, of\, Sight$ $(LOS)$ communication between the two antennas,the height of the transmitting antenna $h$ must be ....... $m$. (Radius of the Earth $R = 6400 \ km$)

For an $FM$ carrier with a carrier frequency of $200 \text{ kHz}$ and a modulating frequency of $10 \text{ kHz}$,the modulation index is...