In: Physics
The conductivity of carbon is about 3*(10^4) S/m.
a. What size and shape sample of carbon has this conductance? (Conductance is equal to 1/R).
b. What is the conductance if every dimension of the sample found in (a) is cut in half?
Conductivity is the inverse of resistivity. So, if the
condictivity is then the
resistivity is
Resistance is given by the equation
where
is the
resistivity, L is the lenght of the sample and A is the cross
sectional area of the face, through which the current is
flowing.
a)Let the conductance be (since it is
only said "this conductance").
Now, the above equation can be rewritten as
or
where G is the conductance,
is the
conductivity.
Lets assume, for the sake of calculation, that the cross
sectional area is , and that face is
a square of side 1m.
then
or
b) Now, we have a cube of side 1m. if we change the side of the
cube to 0.5m (half the value of original), then the cross sectional
area becomes
and its length becomes 0.5m.
The new conductance will be given by