Magnetic field question

[JD7]

A straight wire is placed on a table and a circular wire is positioned surrounding it. Once a switch is closed, the wires begin to carry current in the directions depicted below:

Once the current begins to flow, the straight wire will:

1. accelerate to the left.
2. accelerate to the right.
3. move, but with a constant velocity.
4. remain stationary.
   
   
   
   I had a clear idea on how the 2 magnetic fields behaved, I don't understand how these 2 magentic fields will act on each other....
   
   
   
   Spoiler

   A correct - Using the right hand rule, we can determine that the circular wire is causing a magnetic field to be generated into the page within the circle and out of the page outside the circle. Since, the straight wire is within the circle, it experiences an into-page B-field. Now, using another right hand rule, this current carrying wire in this magnetic field will experience a force (i.e. accelerate) to the left.
   B) True if either current direction were reversed.
   C) No, the magnetic field produces a force on the straight wire: a force means acceleration.
   D) No, the magnetic field produces a force on the straight wire: a force means acceleration.

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[MT Headed]

I had a clear idea on how the 2 magnetic fields behaved, I don't understand how these 2 magentic fields will act on each other....

The magnetic fields don't interact in the analysis of the straight wire forces. The circular wire creates a magnetic field. The straight wire has a current.

If you have a current of "north" and a magnetic field of "into the page" the force experienced by the current carrying wire is "west".

 

[JD7]

"east"? The answer says west.

 

[milski]

"east"? The answer says west.

I'm fairly sure he meant 'west'. Or he has very fancy hands. 🙂

Thumb up, index into the page, middle finger to the left/west.

 

[JD7]

I'm fairly sure he meant 'west'. Or he has very fancy hands. 🙂

Thumb up, index into the page, middle finger to the left/west.

how can I determine its left? I know it's rotating clockwise (depending on the perspective) while the current is going up. I'm still having a hard time grasping this exercise.

The "into the page" is obvious though.

 

[MT Headed]

For the magnetic field in the loop, use your right hand and curl your fingers in the direction of the current. Your thumb points into the page. This is the direction of the magnetic field induced in the loop by the circular, clockwise current.

For the force experienced by the straight wire, use your right hand again. This time point your fingers in the direction of the current (north) and then bend your fingers down into the page. The only way you can accomplish this motion is if your thumb is pointing west (left). This is the direction of the net force experienced by the current carrying straight wire.