A slab of material is to be tested to decide whether it should be used as the central layer of a high-voltage capacitor.
The slab is cut into a small block and placed successively in four separate experimental setups:
1. The block is inserted between the jaws of a sensitive ohmmeter and the reading does not change.
2. The block is suspended by an insulating thread and placed in a strong electric field; it is observed to align itself, but no charge can be drawn off its surface by a proof plane.
3. One face of the block is momentarily touched with a charged metal sphere; after separation the block shows no repulsion for identical spheres brought near that face.
4. The block is given a slight scratch on one face and then connected to the positive terminal of an EHT power supply; a voltmeter connected between the scratched face and earth shows a steady reading.
Answer the following questions concerning these observations.
a. (i) From the evidence in the four setups, identify whether the material behaves as a conductor or a dielectric. Give reasons for each observation cited above.
b. (ii) Distinguish clearly between free charges and bound charges. State which type of charge is responsible for the alignment observed in setup 2.
c. (iii) Explain why a conductor placed in a static electric field develops no electric field within its bulk, whereas a dielectric does. Relate your explanation to the mobility (or lack of mobility) of charge carriers in the two materials.