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    Doubling the length causes the resistance to double hence :

    2R

    Simultaneously, doubling the radius would cause the resistance to be 1/4 of its original value, correct ?

    Hence :

    R/4

    I dont know how to proceed after this.
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    (Original post by Ari Ben Canaan)
    Doubling the length causes the resistance to double hence :

    2R

    Simultaneously, doubling the radius would cause the resistance to be 1/4 of its original value, correct ?

    Hence :

    R/4

    I dont know how to proceed after this.
    You're right about it. Resistance increases by a factor of 2 and at the same time decreases by a factor of 4. This means that the overall increase is by a factor of 2/4. Can you see that?
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    so if you do them both

    x2 x1/4 = x1/2 overall. so the answer is B
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    Doubling the length give R x 2, yes, and doubling the radius gives R x 1/4 -Correct.
    The combined effect will be
    2 x 1/4

    Edit
    Wow. 3 simultaneous answers.
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    (Original post by teachercol)
    so if you do them both

    x2 x1/4 = x1/2 overall. so the answer is B
    Did you simply multipl 2x and x/4 ? If so, why ?

    (Original post by jaroc)
    You're right about it. Resistance increases by a factor of 2 and at the same time decreases by a factor of 4. This means that the overall increase is by a factor of 2/4. Can you see that?
    No, I'm really sorry, I cant seem to see how the increase is 2/4.
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    (Original post by Stonebridge)
    Doubling the length give R x 2, yes, and doubling the radius gives R x 1/4 -Correct.
    The combined effect will be
    2 x 1/4

    Edit
    Wow. 3 simultaneous answers.
    Once again, why did you multiply the two ?
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    Because if one thing doubles R and the other thing makes R 4 times less, then doing both things does one followed by the other.
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    (Original post by Ari Ben Canaan)
    Once again, why did you multiply the two ?
    You have £100

    I first double your money, then I quarter it.
    How much do you have left?

    100 x 2 = 200
    then
    200/4 = 50

    I could also say 100 x 2 x 1/4
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    (Original post by Stonebridge)
    You have £100

    I first double your money, then I quarter it.
    How much do you have left?

    100 x 2 = 200
    then
    200/4 = 50

    I could also say 100 x 2 x 1/4
    Damn it.... I see the light now.

    Thank you to all of you.

    +rep to all.
 
 
 
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