Electric Forces and Electric Fields PDF

Chapter 15 Electric Forces and Electric Fields 18.6 The Electric Field An electric field is said to exist in the region of space around a charged object. – When another charged object enters this electric field, the field exerts a force on the second charged o...

Chapter 15 Electric Forces and Electric Fields 18.6 The Electric Field An electric field is said to exist in the region of space around a charged object. – When another charged object enters this electric field, the field exerts a force on the second charged object. This test charge should have a small magnitude so it doesn’t affect the other charge. 18.6 The Electric Field A charged particle, with charge Q, produces an electric field in the region of space around it. A small test charge, qo, placed in the field, will experience a force. 18.6 The Electric Field DEFINITION OF ELECRIC FIELD The electric field that exists at a point is the electrostatic force experienced by a small positive test charge placed at that point divided by the charge itself:   F E qo SI Units of Electric Field: newton per coulomb (N/C) The electric field is a vector quantity The direction of the field is defined to be the direction of the electric force that would be exerted on a small positive test charge placed at that point. 18.6 The Electric Field The electric field produced by a negative charge is directed toward the charge. – A positive test charge would be attracted to the negative source charge. 18.6 The Electric Field The electric field produced by a positive charge is directed away from the charge. – A positive test charge would be repelled from the positive source charge. 18.6 The Electric Field direction summary 18.7 Electric Field Lines Electric field lines or lines of force provide a map of the electric field in the space surrounding electric charges. 18.7 Electric Field Lines Electric field lines are always directed away from positive charges and toward negative charges. 18.7 Electric Field Lines 18.7 Electric Field Lines Rules for Drawing Electric Field Lines The lines for a group of charges must begin on positive charges and end on negative charges. – In the case of an excess of charge, some lines will begin or end infinitely far away. The number of lines drawn leaving a positive charge or ending on a negative charge is proportional to the magnitude of the charge. No two field lines can cross each other. 18.7 Electric Field Lines An electric dipole consists of two equal and opposite charges. The high density of lines between the charges indicates the strong electric field in this region. 18.7 Electric Field Lines 18.7 Electric Field Lines Unequal and unlike charges Note that two lines leave the +2q charge for each line that terminates on –q 8 lines 16 lines 18.7 The Electric Field lines Activity: In each of the following sets of point charges that are placed together, sketch (draw) electric field patterns around the charges: +1 C and -2 C, -1 C and +2 C, +2 C and -6 C,