Rheostat
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Imagine diagram below is a rheostat
A _____________C____________ B
AB is the piece of wire while C is point of contact.
May I know what's essental in the construction of this rheostat.
A. a constant cross sectional-area of wire from A to B
B. Type of wire used
C Length of AB
D None of the above
Intially I thought answer's C. But think again, if the cross sectional area's not constant, then the length(where you move) doesn't matter since resistance changes unevenly everything you move! The area's affecting it all the time. Say you have a rheostat that intially a large area, small area, large area, larger area, then SMALLER area. In this case, current is always varying! However, length matters but not as much because as long as you have a piece of wire, if you say move it a little towards A, resistance decreases, and current increases and vice versa for B. You can control the current so long as you have a wire. (it all depends on how well you move it to get your desired flow of current across) Thus I think A is the answer.
What's your take? (:
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You have to ask yourself what a rheostat is for.
Yes, you are pretty much correct. Rheostat is used to differ electrical resistance in a circuit.
Type of wire is out.
Length of AB wouldn't really matter since you can have a 1 km long wire but your point of contact is defined at where you want it to be.
I think A is the answer too. Nice analysis.
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unless a proportion of length to resistance is required, other than that, why would we need to have constant cross-sectional area for a rheostat if it is used merely to change the electrical resistance?
Do think about it
