17.2 and 17.3 Electric Forces and Fields
pp. 635 - 552
Mr. Richter
Agenda
 Warm Up
 Review HW
 Discuss Upcoming Schedule
 Notes:
 Electric Force
 Electric Fields
 Electric Field Lines
Objectives: We Will Be Able To…
 Calculate electric force using Coulomb’s law.
 Calculate electric field strength.
 Draw and interpret electric field lines.
Warm-Up:
 What is a field force? Use your book if necessary (try the
index!).
Electric Force
Electric Force
 Electric charges are attracted to and repelled by each other.
 This pull or push is an electric force exerted on each
charge.
 The magnitude of the electric force depends on:
 the size of the charges (how many extra electrons or protons)
 the distance between the charges
Electric Force: Coulomb’s Law
 The magnitude of the force between two charges can be
calculated using Coulomb’s Law.
N × m2
 kC is the Coulomb constant: 8.99 ´10
C2
9
Electric Force: Your Turn
 The electron and proton of a hydrogen atom are separated,
on average, by a distance of about 5.3 x 10-11 m. What is the
magnitude of the electric force each particle exerts on the
other?
 Find the magnitude of the charges on p. 630.
 Felectric = 8.2 x 10-8 N
Electric Fields
Electric Fields
 Electric forces are field
forces. Meaning that:
 No physical contact is
necessary.
 Acts in all direction at
once.
 All charged objects create
electric fields that surround
them.
 An electric field is the region in space where any charged object
feels an electric force.
Electric Fields
 The electric field strength (E) is a ratio of force to charge.
 How many Newtons of force does each Coulomb of charge
experience?
only for relatively large fields
 Units of electric field strength are [N/C]
Electric Field Lines
Electric Field Lines
 To visualize the electric field, electric
field lines are drawn.
 Rules:
 Lines are drawn from positive charge to
negative.
 Number of lines drawn in proportional to
strength of charge.
 Lines do not cross.
Electric Field Lines
 Electric field lines show the combinations of electric fields
from more than one charge.
 Opposite, equal charges.
Electric Field Lines
 Electric field lines show the combinations of electric fields
from more than one charge.
 Like, equal charges.
Electric Field Lines
 Electric field lines show the combinations of electric fields
from more than one charge.
 Opposite, unequal charges.
Wrap-Up: Did we meet our objectives?
 Calculate electric force using Coulomb’s law.
 Calculate electric field strength.
 Draw and interpret electric field lines.
Homework
 p. 636 #3, 4
 p. 656 #41, 42
 p. 657 #55