Compass , current carrying coil

[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 ?

 

[berkeman]

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

 

[aliserwan]

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

so answer is a ?

 

[berkeman]

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?

 

[aliserwan]

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?

 

[berkeman]

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...

 

[aliserwan]

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.

 

[berkeman]

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

 

[berkeman]

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