a copper wire has a square cross section 2.0 mm on a side. it is 4m connected to a power supply of 10v, the resistivity of copper is 1.7*10^-8 Ω what is the current density

  1.47·10^8 A/m^2

Explanation:

The current density is ...

  J = E/(ρ·L) = 10 V/((1.7·10^-8 Ω·m^2/m)(4 m)) = 1.47·10^8 A/m^2

when insulating materials rub against each other, they may become electrically charged . electrons , which are negatively charged, may be 'rubbed off' one material and on to the other. the material that gains electrons becomes negatively charged. the material that loses electrons is left with a positive charge.

answer would be letter choice (a),   a ball resting on a shelf. would be another example of potential energy   >   stored energy > not moving.

a ball spinning on a finger   >   kinetic energy > moving energy

a ball rolling on the ground   >   kinetic energy   > moving energy

a   ball flying through the air   > kinetic energy   >   moving energy

hope that                                         : )