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A wire contains a steady current of 2 A. The number of electrons that pass a cross...

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alainnass | Student, Undergraduate | Honors

Posted September 5, 2012 at 2:00 AM via web

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A wire contains a steady current of 2 A. The number of electrons that pass a cross section in 2 s is:

A)    2
B)    4
C)    6.3 × 1018
D)    1.3 × 1019
E)    2.5 × 1019

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Mary Joy Ripalda | High School Teacher | (Level 3) Educator

Posted September 5, 2012 at 3:01 AM (Answer #1)

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Ampere(A) is defined as Coulomb per second(C/s). Its formula is:

`I=Q/t`

where I -  current, Q-charge, and t-time.

Substitute I=2 A and t=2 s  to determine the charge passing through the wire.

`2=Q/2`

`4=Q`

So, the charge is Q=4C.

To determine the number of electrons, take note of the conversion factor:

(1 electron) `1e=-1.6x10^(-19)C`

Using this yields,

`4C * (1e)/(-1.6x10^(-19)C) = -2.5x10^19 e`

Take the positive value of e.

Hence, the number of electrons that pass though the wire's cross section is (E) `2.5x10^19 ` .

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