[填空题]
1.The diagram below shows a small section of wire which is a part of a closed electric circuit.
Due to a potential difference across the circuit, an electric field exists in the wire, as shown. Explain, in terms of the charge carriers, why current exists in the wire.
2.The electric field is due to a potential difference of $120\,V$ across the circuit. If the field performs $600\,J$ of work moving negative charges over a time period of 2 seconds, show that approximately $3\times10^{19}$ electrons move through a cross-section of wire in this time.$\,$$\,$$\,$The number of electrons represented by this charge is $\times10^{19}$
3.Calculate the current in the wire.I= A
4.If the density of mobile electrons in this wire segment is $8\times10%{28}$ electrons $m^{−3}$, and the wire has a diameter of $2.6\,mm$, calculate the drift speed of the electrons in the wire.$v$= $\times10^{-5}ms^{-1}$
