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# Resistance of wire - varies with area ? watch

1. 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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2. (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?
3. so if you do them both

x2 x1/4 = x1/2 overall. so the answer is B
4. 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
5. (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.
6. (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
Once again, why did you multiply the two ?
7. 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.
8. (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
9. (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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