What is the field in a cavity if a conductor having a cavity is charged? Does the result depend on the shape and size of the cavity or conductor?

Hint: A conductor is a material which has a large number of free electrons available for the passage of current. Due to the large number of electrons, the force of repulsion acting in between them is also very high. Hence in order to minimize the repulsion between electrons, the electrons move to the surface of the conductor. Hence we can say that net charge inside the conductor is zero.

Complete step by step answer:
Irrespective of the shape and size of the conductor, all the charge resides on the outer surface of the conductor. This concept is valid even if we apply an external electric field on the conductor. But by placing a conductor in an external electric field, we observe a change in the alignment of charges internally. To nullify the effect of the external electric field, negative charges and proportional positive occupy opposite sides of the conductor’s surface so that the field created by these charges nullifies the effect of the external field so the net field inside is still zero. This whole phenomenon is such that “When a conductor is placed inside an electric field, the charges inside the conductor arrange themselves in such a fashion, that electric field inside the conductor becomes zero”. This phenomenon is called electrostatic shielding.

Hence net electric field is zero inside the cavity in a conductor, irrespective of shape, size or location of the cavity.

Note:
This result is true for any shape and size of conductor. Students are advised to revise properly the properties of conductor as it has unique properties that are needed to be understood properly and keep in mind all the properties of the conductor while attempting a question related to it.