Aparallel-plate air capacitor has a capacitance of 920 pf. the charge on each plate is 3.90 μc. what is the potential difference between the plates? express your answer with the appropriate units. part b if the charge is kept constant, what will be the potential difference between the plates if the separation is doubled? express your answer with the appropriate units. part c how much work is required to double the separation? express your answer with the appropriate units (mj)

a)235.9*10^-6 V; b) 471.8 *10^-6 V; c) 1.08*10^-13 J

Explanation: In order to explain this problem we have to use the expression for a capacitor od two parallel plates, which is given by:

C=Q/V where Q and V are the charge and voltage difference in teh capacitor, respectively.

Then we have;

V=Q/C=920*10^-12/(3.9*10^-6)= 235.9*10^-6 V

If we double the separation between the plates, the potencial difference will be:  ( Q is constant)

Vnew=Q/Cnew  where Cnew is given by;

Cnew=ε *A/(2*d) = 1/2*(ε *A/d)=1/2* Co ; then:

Vnew=2*Q/(Co)=2*Vo=2*4.24 *10^3 V=471.8 *10^-6 V

Finally, the work made oin the capacitor is the difference of the final and initial potential energy so:

Uo=Q^2/(2Co)=

Uf= Q^2/(2Cnew)               Cnew=Co/2

W=Uf-Uo= Q^2(1/Co)-Q^2(1/2*Co)=Q^2(1/2*Co)=1.08*10^-13 J

electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with barriers made of conductive or magnetic materials. shielding is typically applied to enclosures to isolate electrical devices from their surroundings, and to cables to isolate wires from the environment through which the cable runs. electromagnetic shielding that blocks radio frequency electromagnetic radiation is also known as rf shielding.

the shielding can reduce the coupling of radio waves, electromagnetic fields and electrostatic fields. a conductive enclosure used to block electrostatic fields is also known as a faraday cage. the amount of reduction depends very much upon the material used, its thickness, the size of the shielded volume and the frequency of the fields of interest and the size, shape and orientation of apertures in a shield to an incident electromagnetic

from wikipedia