What is the difference between current and current density?
Charge moves through a wire at a rate known as current.
The density of current flow within the conductors is called current density
A conductor's current is defined as the rate at which electric charges flow through it. Current density is defined as the volumetric flow of charge per unit area through a conductor.
Difference between current and current density:
The current flow is sustained by an established electric field.
Here, is current in Ampere, is charge in Coulomb, and is time in seconds.
The current density written as follows.
Here, is current density in is current in Amperes, and is area of conductor in
Hence, In conductors, the current density can be defined as the density of current flow within the conductors. A stable current means that its magnitude and direction will always remain the same.
The conductive tissues of the upper leg can be modeled as a 40-cm-long, 12-cm-diameter cylinder of muscle and fat. The resistivities of muscle and fat are 13 Ω m and 25 Ω m, respectively. One person’s upper leg is 82% muscle, 18% fat. What current is measured if a 1.5 V potential difference is applied between the person’s hip and knee?
The resistivity of a metal increases slightly with increased temperature. This can be expressed as , where T0 is a reference temperature, usually 20°C, and a is the temperature coefficient of resistivity.
a. First find an expression for the current I through a wire of length L, cross-section area A, and temperature T when connected across the terminals of an ideal battery with terminal voltage ∆V. Then, because the change in resistance is small, use the binomial approximation to simplify your expression. Your final expression should have the temperature coefficient a in the numerator.
b. For copper, a = 3.9 * 10-3 °C-1 . Suppose a 2.5-m-long, 0.40-mm-diameter copper wire is connected across the terminals of a 1.5 V ideal battery. What is the current in the wire at 20°C?
c. What is the rate, in A/°C, at which the current changes with temperature as the wire heats up?
76. A thin metal cylinder of length and radius is coaxial with a thin metal cylinder of length and a larger radius . The space between the two coaxial cylinders is filled with a material that has resistivity . The two cylinders are connected to the terminals of a battery with potential difference , causing current to flow radially from the inner cylinder to the outer cylinder. Find an expression for the resistance of this device.
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