two concentric metallic spherical shells of radii R and 2R are given charges Q1 and Q2 respectively .the surface charge densities on the outer surfaces of the shells are equal .determine the ratio Q1:Q2

                                             
      Surface Charge density ,σ = charge / surface area
      Surface Charge density of the metallic shell of radius R and charge Q₁ is
                                          σ₁ = Q₁/4πR²  
      Similarly, Surface Charge density of the metallic shell of radius 2R and charge Q₂,
                                          σ₂ = Q₂/4π(2R)²  

                             Given,   σ₁  = σ₂

                                   $$\begin{gathered} \frac{Q_1}{4{\mathrm{\pi R}}^2}=\frac{Q_2}{4\mathrm{\pi }(2\mathrm{R}{)}^2} \\ \frac{ Q1}{Q2} = \frac{1}{4} \end{gathered}$$