Show that the dielectric constant of a conductor can be taken to be infinitely great.

For a hypothetical electronic device, the potential difference $\Delta V$, measured across the device, is related to the current $i$ by $\Delta V=\left(3.55 \times 10^6 \mathrm{~V} / \mathrm{A}^2\right) i^2$. $(a)$ Find the resistance when the current is $2.40 \mathrm{~mA}$. (b) At what value of the current is the resistance equal to $16.0 \Omega$ ?

Would you expect the dielectric constant of a material to vary with temperature? If so, how? Does whether or not the molecules have permanent dipole moments matter here?

Can a dielectric conduct electricity? Can a conductor have dielectric properties?

Using data from given figure, plot the resistance of the $p n$ junction diode as a function of applied potential difference.

Carbon has a negative temperature coefficient of resistivity. which means that its resistivity drops as its temperature increases. Would its resistivity disappear entirely at some high enough temperature?

Copper and aluminum are being considered for a high-voltage transmission line that must carry a current of $62,3 \mathrm{~A}$. The re. sistance per unit length is to be $0.152 \Omega / \mathrm{km}$. Compute for each choice of cable material $(a)$ the current density and (b) the mass of $1.00 \mathrm{~m}$ of the cable. The densities of copper and aluminum are 8960 and $2700 \mathrm{~kg} / \mathrm{m}^3$, respectively.

In the lower atmosphere of the Earth there are negative and positive ions, created by radioactive elements in the soil and cosmic rays from space. In a certain region, the atmospheric electric field strength is $120 \mathrm{~V} / \mathrm{m}$, directed vertically down. Due to this fieid, singly charged positive ions, 620 per $\mathrm{cm}^3$. drift downward, and singly charged negative ions, 550 per $\mathbf{c m}^3$, drift upward. The measured conductivity is $2.70 \times 10^{-14} / \Omega \cdot \mathrm{m}$. Calculate $(a)$ the ion drift speed, assumed to be the same for positive and negative ions; and (b) ie current density.

From a student's paper: "The relationship $R=\Delta V / i$ tells you that the resistance of a conductor is directly proportional to the potential difference applied to it." What do you think of this proposition?

When a potential difference of $115 \mathrm{~V}$ is applied between the ends of a $9.66-\mathrm{m}$-long wire, the current density is $1.42 \mathrm{~A} / \mathrm{cm}^2$. Calculate the conductivity of the wire material.

The character and quality of our daily lives are influence greatly by devices that do not obey Ohm's law. What can you say in support of this claim?

The electric potential $V$ in the space between the plates of a particular, and now obsolete, vacuum tube is given by $V=$ $\left(1530 \mathrm{~V} / \mathrm{m}^2\right) \mathrm{x}^2$, where $x$ is the distance from one of the plates. Calculate the magnitude and direction of the electric field at $x=1.28 \mathrm{~cm}$

A copper wire and an iron wire of the same length have the same potential difference applied to them. (a) What must be the ratio of their radii if the current is to be the same? $(b)$ Can the current density be made the same by suitable choices of the radii?

Why does an incandescent lightbulb grow dimmer with use ?