# Distance between the rods??? It changes! (1 Viewer)

#### donrob15

##### New Member
the part before the distance calculation - did it ask to find the mass or the weight of the rod? i think i only found the mass (from the graph = easy)...but didnt time it by 9.8...i timesd it by 9.8 in the distance calculation though. oh well nothing i can do now.

#### Fobio

##### New Member
Wackedupwacko said:
mass doesnt change to work it out... just draw ur graph to touch the y axis as stated. then i think the distance is worked out by

F=mg = (formula the I1I2 which i cant be bothered to write)

this occurs when the balance reads 0kg which you can work out from the graph... mine suggested abotu 4392 A needed for it. chuck that as your I2 in ..... got about 0.2m or 0.02 cant remmeber which atm..... head spinnning
DATS!!!
huo

#### arkanisw

##### New Member
dimivat said:
For the question that asks the distance between the rod, if the mass they gives you decreases with the increase in current doesn't that mean the distance is changing as a result of the second rod being atracted to the first?
What I did:

the reading on the scale, R, reads Rg as resultant force. ie

Weight pulling rod down - Force pulling rod up = Rg

mg - F = Rg

elementary maths tells us :

-ΔF = ΔRg

but F = kLI1I2/d

the only change is in current, (distance doesnt change)

making:

-ΚLI1(ΔI2/ΔR)/g = d

ΔR/ΔI2 is of cause the gradient of the graph.

so you just sub it all in..

there we go, sorry, but i am 4U math, i prefer to derive everything.