Join TSR now and get all your revision questions answeredSign up now
    • Thread Starter
    Offline

    0
    ReputationRep:
    Can someone please help me with this question?

    I dont understand why its multiplied by pie! Pie is only a constant and it isnt an uncertainty, so whyyy?

    Name:  ImageUploadedByStudent Room1397605552.049033.jpg
Views: 74
Size:  109.5 KB
    Name:  ImageUploadedByStudent Room1397605560.518344.jpg
Views: 72
Size:  98.1 KB


    Posted from TSR Mobile
    Attached Images
      
    Offline

    3
    (Original post by jtbteddy)
    Can someone please help me with this question?

    I dont understand why its multiplied by pie! Pie is only a constant and it isnt an uncertainty, so whyyy?

    Name:  ImageUploadedByStudent Room1397605552.049033.jpg
Views: 74
Size:  109.5 KB
    Name:  ImageUploadedByStudent Room1397605560.518344.jpg
Views: 72
Size:  98.1 KB


    Posted from TSR Mobile

    You haven't posted the beginning of the question but...
    You are confusing absolute uncertainty with % uncertainty.

    If the absolute uncertainty in a number is, say, 2.0 ± 0.1
    and you multiply it by any other number
    the absolute uncertainty is also multiplied by that number.

    So if I multiply by 10 I get
    20 ± 1

    The % uncertainty stays the same.
    The % uncertainty in 2.0 ± 0.1 is ±5%

    It's the same % uncertainty in 20 ± 1
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Stonebridge)
    You haven't posted the beginning of the question but...
    You are confusing absolute uncertainty with % uncertainty.

    If the absolute uncertainty in a number is, say, 2.0 ± 0.1
    and you multiply it by any other number
    the absolute uncertainty is also multiplied by that number.

    So if I multiply by 10 I get
    20 ± 1

    The % uncertainty stays the same.
    The % uncertainty in 2.0 ± 0.1 is ±5%

    It's the same % uncertainty in 20 ± 1
    Okayy. And if the other value, e.g. If 10 is the length of something with uncertainty +-0.2 mm, id add the uncertainties of both values to get the conbined uncertainties?

    And what if i would do pie/2, would i divide pie by the uncertainty of 2 to get the absolute uncertainty? Similarly, what would i do if id add or subtract both values?

    Posted from TSR Mobile
    Offline

    3
    (Original post by jtbteddy)
    Okayy. And if the other value, e.g. If 10 is the length of something with uncertainty +-0.2 mm, id add the uncertainties of both values to get the conbined uncertainties?

    And what if i would do pie/2, would i divide pie by the uncertainty of 2 to get the absolute uncertainty? Similarly, what would i do if id add or subtract both values?

    Posted from TSR Mobile
    The rules are
    If you have two values with uncertainties and you need to add the values together you also add the uncertainties.
    You also add the uncertainties if you have to subtract the values.

    If you multiple or divide two values you add the % uncertainties in those values to get the % uncertainty in the result.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Stonebridge)
    The rules are
    If you have two values with uncertainties and you need to add the values together you also add the uncertainties.
    You also add the uncertainties if you have to subtract the values.

    If you multiple or divide two values you add the % uncertainties in those values to get the % uncertainty in the result.
    So if i add or subtract, i add the absolute uncertainties and when i multiply or divide, i add the percentage uncertainties?

    Posted from TSR Mobile
    Offline

    3
    (Original post by jtbteddy)
    So if i add or subtract, i add the absolute uncertainties and when i multiply or divide, i add the percentage uncertainties?

    Posted from TSR Mobile
    Exactly.
    That's the rule.
    This question comes up again and again on here, so a quick search for "uncertainties" in this forum will probably dig up a number of threads with examples of this which might help.
    • Thread Starter
    Offline

    0
    ReputationRep:
    (Original post by Stonebridge)
    Exactly.
    That's the rule.
    This question comes up again and again on here, so a quick search for "uncertainties" in this forum will probably dig up a number of threads with examples of this which might help.
    Ill do that now- thanks

    Posted from TSR Mobile
 
 
 
Poll
Should MenACWY vaccination be compulsory at uni?

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.