Final answer:
The electric field just outside a conducting shell is zero due to the rearrangement of charges on the inner surface of the shell.
Step-by-step explanation:
The electric field just outside a conducting shell is zero. This is because the charges on the inner surface of the shell rearrange in response to the presence of the charge in the cavity, creating an opposite electric field that cancels out the electric field of the cavity charge. Therefore, the strength of the electric field just outside the conducting shell is zero.