Currents in Solids

1. Some copper fuse wire has a diameter of 0.22mm and is designed to carry currents of up to 5.0 A. If there are 1.0 x 10²⁹ electrons per m³ of copper, what is the mean drift speed of the electrons in the fuse wire when it carries a current of 5.0A?
2. A wire carrying an electric current will overheat if there is too large a current: the accepted value for the maximum allowable current in a copper wire is 1.2 x 10⁷ A per square metre of cross-section of the wire. If there are 1.0 x 10²⁹ electrons per m³ of copper, calculate the mean drift speed of the electrons in the wire when the current reaches this value.
3. Two copper wires of diameter 2.00 mm and 1.00mm are joined end-to-end. What is the ratio of the average drift speeds of the electrons in the two wires when a steady current passes through them? In which wire are the electrons moving faster?
4. A copper wire joins a car battery to one of the tail lamps and carries a current of 1.8A. The wire has a cross-sectional area of 1.0 mm² and is 6.0 m long. If there are 1.0 X 10²⁹ electrons per m³ of copper, calculate how long it takes an electron to travel along this length of wire.