1. A copper wire 96.3 cm long and 1.07 mm in diameter has a mass of 6.25 g. (a)

Question

1. A copper wire 96.3 cm long and 1.07 mm in diameter has a mass of 6.25 g.

(a) Find the number of electrons in the wire. (Copper has an atomic number of 29; that is, there are 29 protons in the Copper atom. Copper's atomic mass is 63.5.)

(b) There is one free electron per atom in copper. Find the number of free electrons in the wire.

2.Find the electric field at P in the figure shown below. (Take r = 1.2 m and = 36°. Measure the angle counterclockwise from the positive x-axis.) (q=1/.90 x 10^-9)

3.The earth's surface charge density (1.0 10-9 C/m2) is roughly balanced by a net positive charge in the lower 10 km of the earth's atmosphere. What is the average volume charge density of this atmospheric charge?

4.A thin gold ring of radius 1.03 cm carries a uniform charge per unit length of 1.08e-14 C/m. Find the electric field on the axis of the ring 1.08 cm from the center. As well as the direction (along the axis away from the ring or along the axis towards the ring)

Explanation / Answer

(a) mass of copper= 6.25 g

molar mass of copper= 63.5 g/mol

so the number of moles= 6.25/63.5 =0.0984

the number of copper atoms = 6.022 x1023 x0.0984 = 5.93 x1022 atoms

now there are 29 electrons per copper atom

so total number of electrons = 29 x5.93 x1022 =1.72 x1024

(b) number of free electrons per copper atom= 1

so total number of free electrons= 5.93 x1022

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