A)
The magnetic field at the center of a coil of N turns is given by
where
I is the current in the coil
N is the number of turns
R is the radius of the coil
Here we have
I = 6.5 A is the current in the coil
N = 100 is the number of turns
is the radius of the coil
Substituting,
B) The force points north
The direction of the force on a positive ion in water can be found by using the right-hand rule. In fact, we have:
- Index finger: direction of motion of the ion --> towards east
- Middle finger: direction of magnetic field --> downward
- Thumb: direction of the force --> towards north
So, the force points north.
C)
The magnitude of the magnetic force on a charged particle moving perpendicularly to the field is
where
q is the charge of the particle
v is the velocity
B is the magnitude of the magnetic field
In this case, we have
is the charge
is the velocity
is the magnetic field strength
Substituting,