A metal sphere A of radius ${\mathrm{r}}_1$ charged to a potential ${\mathrm{\varphi }}_1$ is enveloped by a thin walled conducting spherical shell B of radius ${\mathrm{r}}_2$ Then ${\mathrm{\varphi }}_2$ of the sphere A after it is connected by a thin conducting wire to the shell B will be :

• A

  ${\mathrm{\varphi }}_1\left(\frac{{\mathrm{r}}_1}{{\mathrm{r}}_2}\right)$

• B

  ${\mathrm{\varphi }}_1\left(\frac{{\mathrm{r}}_2}{{\mathrm{r}}_1}\right)$

• C

  ${\mathrm{\varphi }}_1\left(1-\frac{{\mathrm{r}}_2}{{\mathrm{r}}_1}\right)$

• D

  ${\mathrm{\varphi }}_1\left(\frac{{\mathrm{r}}_1{\mathrm{r}}_2}{{\mathrm{r}}_1+{\mathrm{r}}_2}\right)$