phy electricity

1. It is clearly stated in the question that the earth wire is missing. If the Live wire touches the metal case, there is no path for current to flow to earth (due to missing of the earth wire). As such, no current will be flowing. The fuse will not be blown.

2. The electric potential on the sphere is determined by two factors: the +ve charge residing on it, and the presence of nearby -ve (induced) charges.
When the sphere is brought nearer to the plate, more induced -ve charges are produced. These induced -ve charges lower the +ve potential of the sphere (which is produced by its own +ve charges). Thus causing its net potential to decrease.

3. If the copper wires are not insulated, short-circuit is produced between one trun of the coil and the adjacent coils. Current will thus by-pass all the turns of the coil.

4. No. The potential difference V across the gap equals to the voltage of the d.c. supply used. The electric field intensity E is affected by the gap width d.
Since V = E.d, the wider the gap, the lower is the electric field intensity. But V will remain unchanged.

5. Yes, it should be, unless the particle is accelerated to very high speed at the beginning.


2014-12-01 13:09:16 補充：
sorry, a typo in Q3.
"..., short-circuit is produced between one turn of the coil and the adjacent TURNS...."

2014-12-04 17:27:12 補充：
Q:why would induced -ve charges lower the +ve potential of the sphere?
A: The -ve charges lowers the potential of space surrounding it. When the sphere is brought close to the induced -ve charges, the potential of the sphere is lowered.