In amplitude modulation, the message signal
$\begin{aligned} & V_m(t)=10 \sin \left(2 \pi \times 10^5 t\right) \text { volts and Carrier signal } \\ & V_C(t)=20 \sin \left(2 \pi \times 10^7 t\right) \text { volts }\end{aligned}$ The modulated signal now contains the message signal with lower side band and upper side band frequency, therefore the bandwidth of modulated signal is  kHz. The value of $\alpha$ is :