91Ó°ÊÓ

If a current of \(80.0 \mathrm{~mA}\) exists in a metal wire, how many electrons flow past a given cross section of the wire in \(10.0\) min? In what direction do the electrons travel with respect to the current?

In the Bohr model of the hydrogen atom, an electron in the lowest energy state moves at a speed of \(2.19 \times 10^{6} \mathrm{~m} / \mathrm{s}\) in a circular path having a radius of \(5.29 \times 10^{-11} \mathrm{~m}\). What is the effective current associated with this orbiting electron?

If the current carried by a conductor is doubled, what happens to (a) the charge carrier density? (b) The electron drift velocity?

A 200-km-long high-voltage transmission line \(2.0 \mathrm{~cm}\) in diameter carries a steady current of \(1000 \mathrm{~A}\). If the conductor is copper with a free charge density of \(8.5 \times\) \(10^{28}\) electrons per cubic meter, how many years does it take one electron to travel the full length of the cable?

An aluminum wire carrying a current of \(5.0 \mathrm{~A}\) has a crosssectional area of \(4.0 \times 10^{-6} \mathrm{~m}^{2}\). Find the drift speed of the electrons in the wire. The density of aluminum is \(2.7 \mathrm{~g} / \mathrm{cm}^{3}\). (Assume three electrons are supplied by each atom.)

An iron wire has a cross-sectional area of \(5.00 \times\) \(10^{-6} \mathrm{~m}^{2}\). Carry out steps (a) through (e) to compute the drift speed of the conduction electrons in the wire. (a) How many kilograms are there in 1 mole of iron?

An electric heater carries a current of \(13.5 \mathrm{~A}\) when operating at a voltage of \(1.20 \times 10^{2} \mathrm{~V}\). What is the resistance of the heater?

Q A person notices a mild shock if the current along a path through the thumb and index finger exceeds \(80 \mu \mathrm{A}\). Compare the maximum possible voltage without shock across the thumb and index finger with a dry-skin resistance of \(4.0 \times 10^{5} \Omega\) and a wet-skin resistance of \(2000 \Omega\).

Nichrome wire of cross-sectional radius \(0.791 \mathrm{~mm}\) is to be used in winding a heating coil. If the coil must carry a current of \(9.25 \mathrm{~A}\) when a voltage of \(1.20 \times 10^{2} \mathrm{~V}\) is applied across its ends, find (a) the required resistance of the coil and (b) the length of wire you must use to wind the coil.

A potential difference of \(12 \mathrm{~V}\) is found to produce a current of \(0.40 \mathrm{~A}\) in a \(3.2-\mathrm{m}\) length of wire with a uniform radius of \(0.40 \mathrm{~cm}\). What is (a) the resistance of the wire? (b) The resistivity of the wire?