What is an  electric current?  In previous science courses you may have learned that an electric current is defined by the collective movement of many, many charges.  The photograph to the right shows a multi-meter, a device for displaying data related to electric current and voltage in a variety of ways.  Many charges make up the electric current that flows through the mulei-meter.  The current, or amount of charge that flows past a fixed point in a one-second interval, is displayed in amperes (A).  The unit of electric current is named for André-Marie Ampère (1775-1836), a French scientist who contributed extensively to our understanding of the relationship between current and magnetic force.

 



Electric Current:  the amount of charge, in coulombs, that passes a fixed point in a conductor in a one-second interval.

I=qt


Quantity

Symbol

SI Unit

electric current

I

ampere (A)

charge of the particle

q

coulombs (C)

interval

t

seconds (s)


   


 

The SI unit of electric current is the ampere (A).  One ampere of current is equivalent to one coulomb of charge passing a fixed point in a conductor in a one-second interval, 1 A = 1 C/s.


Read
Read "Electric Current" on page 602 of the textbook.


Magnetic Force Direction

 

Recall from Lesson 2 that a moving charge induces a magnetic field and that when this magnetic field encounters an external magnetic field, the two fields will interact and cause the moving charge to experience a magnetic force (both magnitude and direction).

 

The hand rule used to predict the direction of the magnetic force acting on a charged particle in Lesson 2 can be used in a similar way to predict the direction of magnetic force acting on a current-carrying wire.

 

Watch and Listen

Complete the tutorial Force on a Wire.  The tutorial demonstrates how the hand rule is applied to determine the direction of the magnetic force that acts on a perpendicular current-carrying conductor in a magnetic field.