How do electrons know what to do? 4.1.4 Electric Fields

- + Electric Field Maps Electric fields… exist near CHARGED OBJECTS mapped using a POSITIVE test charge 1 – place test charge 2 – draw arrow in direction pushed 3 – this is the field direction + - + +

Electric Field Maps + -

Electric Field Maps + +

Electric Field Strength Gets WEAKER with distance FORCE exerted per unit CHARGE E r + A B C A > C > B  

Example #1 An object with a charge of -2 coulombs positioned in a uniform electric field experiences a force of -300 newtons. What is the strength of the electric field? E= Fe/q E = -300 N / -2 C E = 150 N/C

Example #2 What is the force experienced by a 0.05 coulomb charge when it is placed in an electric field with a strength of 3 x 103 newtons per coulomb? Fe = Eq F = (3 x 103 N/C)(0.05 C) F = 150 N

Parallel Plates + + + + + + + + + + - - - - - - - - - - - - Field strength… Between plates E  Fe = SAME AT ALL POINTS Outside plates = ZERO + + + + + + + + + + - - - - - - - - - - - -

Hollow Charged Spheres Field strength… Normal field pattern outside ZERO inside E = 0

End of 4.1.4 - PRACTICE