Magnetic Force


Important Equations 

Moving charge in a magnetic field 

The implications of this expression include:

1. The force is perpendicular to both the velocity v of the charge q and the magnetic field B.

2. The magnitude of the force is F = qvB sinθ where θ is the angle < 180 degrees between the velocity and the magnetic field. This implies that the magnetic force on a stationary charge or a charge moving parallel to the magnetic field is zero.

3. The direction of the force is given by the right hand rule. The force relationship above is in the form of a vector product.

Definition provided by HyperPhysics


F = Force on the moving charge 

q = Moving Charge 

V = The velocity of the moving charge 

B = Magnetic Field 

 Magnetic Fields

Force on a moving charge in a magnetic fields

What is a magnetic Field 

 A magnetic field is the area of influence exerted by a magnetic force. This field is normally focused along two poles. These poles are usually designated as north and south. However these directions are not the only two that a magnetic field can have. Most magnetic objects are composed of many small fields called domains. Here are some basic concepts of a magnetic field. The first real study of magnetism started during the 1600s and we are still trying to understand how the magnetic field works                                            

First a magnetic field can not be divided. A magnetic field will always be dipole which means it will have two poles. If you divide a magnet you will only get a smaller magnet with the same two poles. It will only change in its strength. If small enough a magnetic field can be turned around in its orientation by a larger magnetic filed. This is the reason why the domains in a ferromagnetic metal rarely orient in the same direction before being magnetized.

Second a magnetic field is the result of electric currents. An electric current is an electric charge moving in a defined path. This movement is what creates magnetic fields. The current can create a magnetic field as large as the Sun's magnetosphere and as small as the domain of an atom. The important thing to know is that one is the companion of the other. Without an electric field you can’t have a magnetic field.

Definition provided by Universe Today  

Why does it have to be a moving charge?

    You already know the answer.  Have you ever taken two  magnetic and try to and they to put them together, if you have two opposite ends the magnets are attracted, the same ends an there attracted. But what does this have to do with this situation?

     If you remember, magnetic fields are created by moving charges.  So in qV x B the qV is a current, a moving charge, so the equation is nothing more then a mathematical expression of of two magnets interacting. 

More about Magnetic Fields 

Magnetic fields are produced by electric currents, which can be macroscopic currents in wires, or microscopic currents associated with electrons in atomic orbits.

From the force relationship above it can be deduced that the units of magnetic field are Newton seconds /(Coulomb meter) or Newtons per Ampere meter. This unit is named the Tesla. It is a large unit, and the smaller unit Gauss is used for small fields like the Earth's magnetic field. A Tesla is 10,000 Gauss. The Earth's magnetic field at the surface is on the order of half a Gauss.

Definition provided by HyperPhysics

Magnetic Forces on a current carrying wire 

Important Equation 

When the magnetic force relationship is applied to a current-carrying wire, the right-hand rule may be used to determine the direction of force on the wire.

Definition provided by HyperPhysics

What is Current? 

 Current is a flow of electrical charge carriers, usually electrons or electron-deficient atoms. The common symbol for current is the uppercase letter I. The standard unit is the ampere, symbolized by A. One ampere of current represents one coulomb of electrical charge (6.24 x 1018 charge carriers) moving past a specific point in one second. Physicists consider current to flow from relatively positive points to relatively negative points; this is called conventional current or Franklin (as in Ben Franklin) current. Electrons, the most common charge carriers, are negatively charged. They flow from relatively negative points to relatively positive positive points

Definition Provided Cio Midmarket 

Simply put current is the amount of charge moving past a point in space, it doesn't even need a wire in order to move through.

Forces on a current carrying wire in a magnetic field

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