Question

https://www.youtube.com/watch?v=G_nrvqKctMk&index=14&list=PLYVDsiuOZP5onjQVfPF07-xEU7wiSywJc

Answer 1

can anyone explain why kq^2/2a and kq^22b is taken

Answer 2

@Michele_Laino @IrishBoy123 hlp

Answer 3

@UnkleRhaukus @amistre64

Answer 4

@ParthKohli

Answer 5

here is why:
the initial energy is the energy of the electric field generated by our charge q, inside the shell. Now we have the subsequent situation:

Using the theorem of Gauss, we can say that into zone 2 the electric field is zero, whereas into zones 1 and 3 the electric field is given by the subsequent expressions:
\[\Large \begin{gathered}
{E_1} = \frac{{{q^2}}}{{{r^2}}},\quad 0 < r < a \hfill \\
\hfill \\
{E_3} = \frac{{{q^2}}}{{{r^2}}},\quad b < r < + \infty \hfill \\
\end{gathered} \]