Question

What is the current density (in mA/m²) in the wire? Formula.

a) J=I​/A
b) J=A/I​
c) J=I⋅A
d) J=I/R​

Answer 1

Answer: A

The correct formula for current density (J) is: a) J = I / A, because mA stand for milliamper, which is unit of Intensity, and
`m^(2)` is unit of area.

Answer 2

Current density (J) is the current (I) per unit cross-sectional area (A) of a wire, calculated using the formula J = I / A. It is measured in amperes per square meter (A/m²), and the area has to be in square meters for the calculation.

Step-by-step explanation:

The student has asked about the formula for current density in a wire and related questions on calculating the current and the magnetic field in different scenarios involving current within a wire. The correct formula for current density (J) is given by J = I / A where I is the current in amperes and A is the cross-sectional area in square meters. To calculate the current density, convert the area into square meters if given in square millimeters before performing the calculation.

For instance, considering an example where the current (I) is 0.87 A and the cross-sectional area (A) is calculated to be 5.26 mm², which should be converted to 5.26 x 10⁻⁶ m². The current density would then be calculated as:
J = 0.87 A / 5.26 x 10⁻⁶ m² = 165.4 A/m² or 165,400 mA/m².