Hey there! Sign in to join this conversationNew here? Join for free
    • Thread Starter
    Offline

    0
    ReputationRep:
    What am I over looking on this question? The answer on the mark scheme is 'A' but how can you get a negative reading?

    Name:  screenshot20130101at110.png
Views: 66
Size:  72.5 KB
    Offline

    0
    ReputationRep:
    You can get a negative reading because the balance was zeroed after something was put on it.
    • Thread Starter
    Offline

    0
    ReputationRep:
    Knew it would be something stupid I was over looking -.-
    Thank you.
    Offline

    0
    ReputationRep:
    (Original post by ashboot)
    Knew it would be something stupid I was over looking -.-
    Thank you.
    Haha, no problem, physics always has those little annoying things about it!
    • Offline

      9
      The important point in this question is about the force on the wire due to the current in it passing through the magnetic field of the magnets.
      F=BLI
      and as B and L don't change, it's the change in the current that causes this change in the force.
      If you reverse the current you reverse the force.
      If you double the current you double the force.
      That's why, if you reverse and double the current, you get a force twice as large in the opposite direction, giving a double negative reading.
      The positive reading would be the case where the force (of the wire) on the scale pushes downwards, and the negative reading implies the force on the scale is pushing upwards.
     
     
     
  1. See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  2. Poll
    Will you be richer or poorer than your parents?
  3. See more of what you like on The Student Room

    You can personalise what you see on TSR. Tell us a little about yourself to get started.

  4. 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

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