# Current Electricity: Current density

1. Two wires both carry the same current (I). The moving charged particles in both wires are electrons, but the concentration of moving electrons in wire #1 is double the concentration of moving electrons in wire #2.

Under what circumstances will the drift speed of electrons be the same in both wires? Choose the answer that best fits.

A. if the diameter of wire #2 is 4 times the diameter of wire #1

B. if the diameter of wire #2 is 1/sqrt(2) the diameter of wire #1

C. if the diameter of wire #2 is 1/4 the diameter of wire #1

D. if the diameter of wire #2 is sqrt(2) times the diameter of wire #1

2. Two wires are both made of the same material and both carry the same current (I). The cross-sectional area of wire #1 is double the cross-sectional area of wire #2.

Compared to the electric field in wire #2, the electric field in wire #1 is:

A. 2 times greater

B. 1/2 as great

C. 1/4 as great

D. sqrt(2) as great

E. 1/sqrt(2) as great

F. 4 times as great.

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1. Two wires both carry the same current (I). The moving charged particles in both wires are electrons, but the concentration of moving electrons in wire #1 is double the concentration of moving electrons in wire #2. Under what circumstances will the drift speed of electrons be the same in both wires? Choose the answer that best fits.

A. if the diameter of wire #2 is 4 times the diameter of wire #1

B. if the diameter of wire ...

#### Solution Summary

Questions related to electric current, current density and field are discussed in the solution.

Electric current: Drift Speed and the Current Density

1. A small but measurable current of 1.2X10^-10 A exists in a copper wire whose diameter is 2.5mm. The number of charge carriers per unit volume is 8.49X10^28 m^-3. Assuming the current is uniform, calculate the (a) current density and (b) electron drift speed.

2. Near Earth, the density of protons is the solar wind (a stream of particles from the Sun) is 8.70 cm^-3, and their speed is 470km/s.(a) Find the current density of these protons.(b) If Earth's magnetic field did not deflect the protons, what total current would Earth receive?

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