A 40-cm-long high-resistance wire with rectangular cross section 7 mm by 3 mm is connected to a 12-volt battery through
an ammeter, as shown in Figure 20.85. The resistance of the wire is 50 ohms. The resistance of the ammeter and the
internal resistance of the battery can be considered to be negligibly small compared to the resistance of the wire.
Leads to a high-resistance voltmeter are connected as shown, with the - lead connected to the inner edge of the wire, at the
top (location A), and the + lead connected to the outer edge of the wire, at the bottom (location C). The distance along the
wire between voltmeter connections is 5 cm.
(a) On a copy of the diagram, show the approximate distribution of charge.
(b) On a copy of the diagram, draw the electric field inside the wire at the 3 locations marked ×.
(c) What is the magnitude of the electric field at location B?
(d) What does the voltmeter read, both magnitude and sign?
(e) What does the ammeter read, both magnitude and sign?
(f) In a 60-second period, how many electrons are released from the - end of the battery?
(g) There are 1.5 × 1026 free electrons per cubic meter in the wire. What is the drift speed v of the electrons in the
wire?
(h) What is the mobility u of the material that the wire is made of?
(i) Switch meter 1 from being an ammeter to being a voltmeter. Now what do the two meters read?
(j) The 12-volt battery is removed from the circuit and both the ammeter and voltmeter are connected in parallel to the
battery. The voltmeter reads 1.8 volts, and the ammeter reads 20.4 amperes. What is the internal resistance of the
battery?