1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Electric field and coffee maker

  1. Jul 8, 2003 #1

    Dx

    User Avatar

    1) A coffe maker which draws 13.5A of current has been left on for 10 min. what is the net number of electrons that have passed thru the coffe maker.

    [del]Q = I * [del]T = 13.5(600) = 8.1x10^3

    I got this wrong, what happened?


    2) a battery is rated 12V and 160Amp-hours. How much energy does the battery store?

    12V * 160 = 1.9kJ

    I got this wrong, can anyone gimme the correct formula(s) to plug in and solve
     
  2. jcsd
  3. Jul 8, 2003 #2

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    10 minutes is 600 seconds so your answer appears to be assuming that one ampere is "one electron per second". Where did you get that idea.

    I suspect that your text book has definitions of "ampere" and "volt". I recommend that you review them.
     
  4. Jul 8, 2003 #3

    Dx

    User Avatar

    No it doesnt Ivy! It gives me the definition but no examples on solving these questions. I saw that 1A = 1c/s but confused on its formula. I assumed youmultiply but i donno. Can you plz point me in the right direction.
     
  5. Jul 8, 2003 #4

    enigma

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Does the book have the amount of electrons per coulomb?
     
  6. Jul 8, 2003 #5

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Of course it does. Any textbook worth its salt would have it.

    1 Ampere is 1C/s, right?
    And 1 electron has a charge of 1.6x10-19C, right?

    From that you should be able to figure out how many electrons per second correspond to 1 Amp.
     
  7. Jul 9, 2003 #6

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    DX, you have a problem with reading your book. You answer firmly that your book does NOT have a definition of "ampere" and then state
    "I saw that 1A = 1c/s but confused on its formula." That IS a definition of ampere! It says that one ampere means one coulomb of electricity per second. Now you need to look up how many electrons there are in a coulomb. Hint: use the index of your book.

    By the way I asked "where did you get the idea that one ampere mean one electron per second" and you answered that you didn't know the definition. You HAVE to know the definitions of the words in problems before you can do the problems! Grabbing numbers out the problem at random and combining them in random ways is not a good way to solve problems.
     
  8. Jul 9, 2003 #7

    Dx

    User Avatar

    Yes, sometimes I overlook things in the book, it happens. So what, sue me! I made a mistake and so did you by making this personal. Don't worry about me overlooking a simple definition and just remember what goes around comes around mr. index.
    Dx

    And if anyone else feels the same way, you can re-read my post. Man that really offends me "Ask for help and all you get is sarcassim. I didn't comprehend the fact. I asked for help set-up my problem which is what I was asked for help with not a definition." To me, your response didn't help me as i was asking so i was honest when i replied to your post.

    Anyways...h20 under the bridge were cool Ivy!
    Dx :wink:
     
  9. Jul 9, 2003 #8

    Tom Mattson

    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    Chill out, Dx. Ivy is right: You don't seem to like to study. You could easily answer most of the questions you post here by reading (not skimming!) your textbook. Asking questions that are answered in the inside cover of any textbook (eg: "What's the charge on 1kg of protons?") gives the impression that you are lazy.

    That is just not true. You have posted many threads here, and no one has responed with sarcasm. It's called constructive criticism. You need to learn the difference.
     
  10. Jul 9, 2003 #9

    HallsofIvy

    User Avatar
    Staff Emeritus
    Science Advisor

    Not sarcasm (by the way, you spelled it wrong :)) just facts: to do mathematics or physics you have to be PRECISE. I'm not going to sue you- you are the one that will suffer if you do not read your text books: 1) CAREFULLY 2) REPEATEDLY 3) WITH PAPER AND PENCIL AT HAND.

    My comment about knowing the definitions was the best help I can give you: it is not enough to have a general idea what a word means. Definitions in mathematics and physics (and other studies) are WORKING definitions: you use the specific words in the definitions to work problems.

    Now: How many electrons are there in a coulomb?
     
  11. Jul 10, 2003 #10

    Dx

    User Avatar

    I want to publiclly apologize to HallsofIvy for my rude remarks. Your %100 correct Ivy, I am taking a few days off to chill out. I will be around but just reading not posting. Lets just say yesterday wasn't the greayesy of my days, ok. Anyways, You, Tom and pretty much everyone else has been a big help and even though I am getting close to the end of my Physics 2 class I want to say thanks for everything and God help me! Kidding! Seriouly, Thanks!

    Tell you what, dinner on me someday. You never know when you might be setting next to ol dx on a plane or biking the mountains of Spain. YES!

    PEACE OUT!
    dx :wink:

    Oh Yes! Almost forgot: heres your answer.

     
    Last edited by a moderator: Jul 10, 2003
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Electric field and coffee maker
  1. Coffee maker (Replies: 4)

  2. Electric Fields (Replies: 4)

Loading...