# Electric Field in a shell

My current understanding is:

• Electric field inside a metal shell = 0 since the net charge enclosed is zero.

• Electric field inside a conductor =0, but the electric field in a cavity of the conductor can be calculated.

The question I faced states that:

Figure 3: Spherical conducting shell with inner radius a and outer radius b. Point charge q1 is located at the centre of the hollow shell. In Figure 3 the central point charge is q1 = +2Q and there is a net negative charge -Q on the spherical conducting shell. Which of the following statements about the electric field magnitude E is true?

a) E is Q/(4(pi)(Epsilon 0)r^2) for all r > b.

b) E is zero for all r < b.

Shouldn't these both be true then?

2. There is a charge of $2Q$ inside the hollow conductor.
3. In order to make (1) work with (2), charges will have to move through the conductor and emerge on a surface. A particular amount of charge needs to emerge on the inner surface, that with radius $a$. This surface charge has to exactly neutralize the charge in the middle of the cavity.
5. For the far field ($r > b$), remember that with (3) we have exactly canceled the electric field within the conductor, so does the field of the inner charge reach outside ($r > b$)?