Electricity is most commonly conducted in a copper wire. Copper has a density of 8.94 g/cm3, and an atomic weight of 63.546 g/mol, so there are 140685.5 mol/m3. In one mole of any element there are 6.02×1023 atoms (Avogadro’s constant). Therefore in 1 m3 of copper there are about 8.5×1028 atoms (6.02×1023 × 140685.5 mol/m3). Copper has one free electron per atom, so n is equal to 8.5×1028 electrons per cubic metre.
Assume a current I = 3 amperes, and a wire of 1 mm diameter (radius = 0.0005 m). This wire has a cross sectional area of 7.85×10−7 m2 (A = π × (0.0005 m)2). The charge of one electron is q = −1.6×10−19 C. The drift velocity therefore can be calculated:
TBS
Dimensional analysis:
TBS
Therefore in this wire the electrons are flowing at the rate of −0.00028 m/s.
By comparison, the Fermi flow velocity of these electrons (which, at room temperature, can be thought of as their approximate velocity in the absence of electric current) is around 1570 km/s.[2]
In the case of alternating current, the direction of electron drift switches with the frequency of the current. In the example above, if the current were to alternate with the frequency of F = 60 Hz, drift velocity would likewise vary in a sine-wave pattern, and electrons would fluctuate about their initial positions with the amplitude of:
2.1 x 10-6 meter
To summarize, the electrons are moving so slowly it’s almost as if they’re standing still. And in the case of alternating current they are moving back and forth so actually they are standing still. So, ye olde fire hose analogy doesn't uh hold water.
cheerios
Assume a current I = 3 amperes, and a wire of 1 mm diameter (radius = 0.0005 m). This wire has a cross sectional area of 7.85×10−7 m2 (A = π × (0.0005 m)2). The charge of one electron is q = −1.6×10−19 C. The drift velocity therefore can be calculated:
TBS
Dimensional analysis:
TBS
Therefore in this wire the electrons are flowing at the rate of −0.00028 m/s.
By comparison, the Fermi flow velocity of these electrons (which, at room temperature, can be thought of as their approximate velocity in the absence of electric current) is around 1570 km/s.[2]
In the case of alternating current, the direction of electron drift switches with the frequency of the current. In the example above, if the current were to alternate with the frequency of F = 60 Hz, drift velocity would likewise vary in a sine-wave pattern, and electrons would fluctuate about their initial positions with the amplitude of:
2.1 x 10-6 meter
To summarize, the electrons are moving so slowly it’s almost as if they’re standing still. And in the case of alternating current they are moving back and forth so actually they are standing still. So, ye olde fire hose analogy doesn't uh hold water.
cheerios
