Which is heavier , a kilogram of lead or a kilogram of a polystyrene beads ?
2 answers:
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Answer:
d_{b} = 2 d_{a}
Explanation:
The electrical resistance for a cylindrical wire is described by the expression
R = ρ L / A
The area of a circle is
A = π r²
r = d / 2
A = π d²/4
We substitute
R = ρ L 4 /π d²
Let's apply this expression to our case, they indicate that the resistance of wire A is 4 times the resistance of wire B
= 4 R_{b}
We substitute
ρ 4/π ² = 4 (ρ 4/π d_{b}²)
1 / d_{a}² = 4 / d_{b}²
d_{a} = d_{b} / 2
Answer:
Electrons are influenced by internal forces.
-On the temperature, density of electrons per unit of volume and relaxation time.
-The temperature
Explanation:
The Drude model neglects interactions between electrons and ions and with themselves. Those interactions (by which we refer as electromagnetic forces) influence in the random movement and freedom of the electron. So, they could be more restricted or could influence in conductivity more.
The deduction of the resistivity comes from the Ohm's law, which states that the Electric field in the material is proportional to the current density of electrons by a constant, which is the resistivity itself. The equation goes as follows:
Where e refers to electron (or the charge of it), τ is the relaxation time (average time between collisions), m is the mass and n is the density of charges (electrons in this case) per volume. However, experimentally resistivity is also dependent on temperature, which actually influence the relaxation time. The thermal energy influence in the behavior of the electrons, making them collide with phonons, have more randomness and reduced mean free path.