Direction of Compass Needle near a Solenoid

[aadarsh9]

A compass is placed near a solenoid. It is closer to the North pole generated by the coil. The magnetic north is 90 deg relative to the compass and the solenoid. The strength of the solenoid is equal to the strength of the magnetic north. In which direction will the compass needle point?

 

[tiny-tim]

hi aadarsh9! welcome to pf!

tell us what you think, and why (with full explanation), and then we'll comment!

 

[aadarsh9]

Since the current is from X to Y, a north pole will be induced near the compass. I would say that the compass needle will point towards the solenoid but it says that the field strength is equal to that of Earth's magnetic field. I can only eliminate answer D. Then, I am lost. The answer is A according to the book.

 

[tiny-tim]

hi aadarsh9!

magnetic field (like electric field) is a vector, so two magnetic fields add like vectors

 

[aadarsh9]

One component to the right and another one upwards. Is the answer C?

 

[tiny-tim]

One component to the right and another one upwards. Is the answer C?

i'm confused:

C is to the left and upwards …

which one do you mean? ​

 

[aadarsh9]

Sorry, its one component to the left and another one upwards. Is it C?

 

[aadarsh9]

Th book says A :(

 

[rude man]

What you need to know is that th Earth's magnet has its S pole at the North pole. Thus, the needle of a compass has its N side pointing North (approximately).

Use that fact and I think you'll see why the answer is indeed A (compass needle points NE).

 

[tiny-tim]

(just got up :zzz:)

What you need to know is that th Earth's magnet has its S pole at the North pole.

yes!

aadarsh9, do you understand why that is so?

 

[aadarsh9]

Thanks tiny-tim and rude man. I understood it!