Ampere's Law

Ampere’s Law

 

Whenever a total current I passes through an area bounded by a closed curve,  the above relationship is true.  This is called Ampere’s Law.

 

Use the right hand rule:  Point curled fingers in direction of  integration (your choice, usually!).  Thumb pointing up shows direction of “positive” current.

Diagram shows into the page as being positive.

Magnetic Force on a moving charge due to an external  B field

•A moving charge is a magnet.

•It alters the space around it, producing a magnetic field.

• In the presence of an external  magnetic field, the charge will experience a force and change its speed/direction.

Magnetic Force on a moving charge due to an external  B field

 

Fq  = qv X B = qvBsinα

(direction given by right hand rule, units of Newtons)

 

•Only a moving charge experiences a force.

•There must be a component of velocity perpendicular to the external field, or 

F = 0.

 

•The force is mutually perpendicular to v and B.

•The force on a negative moving charge is in the opposite direction to v X B (left hand rule!)

           

 

And did I mention the Force was due to an external  B field???

 

•Recall that a force is an interaction between two objects

•A charge cannot experience a force from its own magnetic field