# Compass , current carrying coil

• aliserwan

#### aliserwan

Homework Statement
Can a straight, current-carrying coil be used as a compass?
Relevant Equations
no equations
a. No, because only permanent magnets are suitable to be used as a compass.
b. Yes, but only if the coil doesn't have an iron core.
c. Yes, but only if the coil can turn easily.

I choose (c) , Is that correct ?

## Answers and Replies

It's a trick question. A coil is not straight.

It's a trick question. A coil is not straight.
so answer is a ?

so answer is a ?
IMHO, the question cannot be answered well until the problem statement is fixed. Is that really the word-for-word problem statement?
They say "straight" and "coil" in the same sentence?

IMHO, the question cannot be answered well until the problem statement is fixed. Is that really the word-for-word problem statement?
They say "straight" and "coil" in the same sentence?

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Lordy, what a poorly asked question. Whatever. (not your fault)

Why do you think the answer is a)? Sometimes when presented with poor questions, you have to pick the best available answer...

Lordy, what a poorly asked question. Whatever. (not your fault)

Why do you think the answer is a)? Sometimes when presented with poor questions, you have to pick the best available answer...
A magnetic rod is required when constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic lodestone. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way.

Homework Statement:: Can a straight, current-carrying coil be used as a compass?
Relevant Equations:: no equations

a. No, because only permanent magnets are suitable to be used as a compass.
b. Yes, but only if the coil doesn't have an iron core.
c. Yes, but only if the coil can turn easily.

I choose (c) , Is that correct ?
I think that in the end, your original answer was correct. They must have been referring to a small-diameter coil that is much longer than its diameter. It would work best if wound on a ferrous rod (that's where the "straight" part comes in, I think), since that maximizes the magnetic field that you get for a given current.

Probably they are referring to a rod-based coil like in the picture below:

https://image.made-in-china.com/2f0j00onJtgBWsEeuf/Ferrite-Core-Magnetic-Bar-Rod-Coil-Inductor.jpg

aliserwan
A magnetic rod is required when constructing a compass. This can be created by aligning an iron or steel rod with Earth's magnetic field and then tempering or striking it. However, this method produces only a weak magnet so other methods are preferred. For example, a magnetised rod can be created by repeatedly rubbing an iron rod with a magnetic lodestone. This magnetised rod (or magnetic needle) is then placed on a low friction surface to allow it to freely pivot to align itself with the magnetic field. It is then labeled so the user can distinguish the north-pointing from the south-pointing end; in modern convention the north end is typically marked in some way.
BTW, this looks like it was copy-pasted from some other source, like maybe Wikipedia? When you do that, you should always provide a link to where you copied it from. That helps to avoid copyright issues, and attribution is the right thing to do anyway.

Just an FYI

aliserwan