Hey there! Sign in to join this conversationNew here? Join for free
x Turn on thread page Beta
    • Thread Starter
    Offline

    12
    ReputationRep:
    A copper wire has a cross sectional area of 2mm^2 and carries a current of 6A calculate the mean drift velocity of electrons in the wire. The charge on an electron is -1.6 x 10^-19 C. The number density of copper atoms (the number of atoms per unit volume) is 8 x 10^28 m-3. Each copper atom provides one conduction electron.

    I did this:

    v = I/nAe

    v = 6/ (8 x 10^28) (2 x 10^-6) (-1.6 x 10^-19) = -3.75 x 10^19

    The actual answer is 3.75 x 10^19

    What did I do wrong?
    Offline

    10
    (Original post by tazmaniac97)
    A copper wire has a cross sectional area of 2mm^2 and carries a current of 6A calculate the mean drift velocity of electrons in the wire. The charge on an electron is -1.6 x 10^-19 C. The number density of copper atoms (the number of atoms per unit volume) is 8 x 10^28 m-3. Each copper atom provides one conduction electron.

    I did this:

    v = I/nAe

    v = 6/ (8 x 10^28) (2 x 10^-6) (-1.6 x 10^-19) = -3.75 x 10^19

    The actual answer is 3.75 x 10^-19

    What did I do wrong?
    Nothing. (I assume you meant 10-19 in your answer. That's what it is. If you did get 1019 check your calculation on the calculator))

    You don't need the minus sign for the charge on the electron, you are only interested in the amount of charge, not whether it's positive or negative in this question.
    If you really want the minus sign, then the minus in the answer simply means that the electron is moving in the opposite direction to that which a positive charge (conventional current) would move.
 
 
 
Reply
Submit reply
Turn on thread page Beta
Updated: March 27, 2013
Poll
Do I go to The Streets tomorrow night?

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.