\(A _{ c }- A _{ m }=80\)
\(\therefore A _{ c }=100\)
\(A _{ m }=20\)
Modulation index \(=\frac{20}{100}=\frac{1}{5}\)
Amplitude of each sideband
\(= A _{ c } \frac{( mod \text { ulation index) }}{2}\)
\(=100 \times \frac{1}{10}=10 \text { volt }\)