True or False Questions A) The larger the E field value inside the conductor is,

Question

True or False Questions

A) The larger the E field value inside the conductor is, the larger the current density will be. The ratio of current density over E field is called resistivity of the conductor.

T or F

B) When the voltage from a wall plug produces a current in the coils of a toaster, when it is turned on, current (charge flow) exists in wires and coils. And those wires and coils are NOT conductors in equilibrium.

T or F

C)The direction of the current is in the same direction of flow of charge carriers inside copper or aluminum. Hint: what are the charge carriers in metal, electrons or protons?

T or F

D) The current I describes how fast charges flow through a cross-sectional area of a wire. It has unit of m/s.

T or F

Explanation / Answer

A) The larger the E field value inside the conductor is, the larger the current density will be. The ratio of current density over E field is called resistivity of the conductor.

False

because we know the relation between the resistivity , electric field and the current density is  

J = E/rho

rho = E/J

checking the units

we know the unit of resistiviy is ohm .m

ohm.m = (V/m)/(A/m^2) = (V/A)m = ohm.m

and J = sigma *E

where sigma is conductivity, we know that the conductivity is reciprocal of resistivity

B) When the voltage from a wall plug produces a current in the coils of a toaster, when it is turned on, current (charge flow) exists in wires and coils. And those wires and coils are NOT conductors in equilibrium.

True

we know that

the induced emf will be developed in the coil when there is a change of current. so they were not in equilibrium

C)The direction of the current is in the same direction of flow of charge carriers inside copper or aluminum. Hint: what are the charge carriers in metal, electrons or protons?

False

By convention the direction of current is in the opposite direction to the electrons .

D) The current I describes how fast charges flow through a cross-sectional area of a wire. It has unit of m/s.

False

if the charges are moving with the large speed then the current is i the amount of the charge crossing the cross sectional area

q = it

i = q/t C/s

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