Lecture 02 – PPT and I-Clicker Questions
Which picture best represents the movement of changes as a negatively charged
object comes near a neutral sphere?
(A)
(B)
(D)
(C)
(E)
Charging objects by induction
Note asymmetric charge
distribution in sphere. Why?
“Ground” – an infinite
source or sink of charge
Note more + charges than
negative. Why?
Balloon “sticking” to wall.
Charges have rearranged
again. Why?
I-Clicker Question
A which point is the TOTAL electric force on a test charge closest to zero?
I-Clicker Question
A which point is the TOTAL electric force on a test charge closest to zero?
I-Clicker Question
Which of the following insights concerning the electric field at a distance D from an
infinite line of charge is true?
(A) Only 1 statement true (B) two are true (C) three are true (D) only 1 is false (E) none
false
•
•
•
•
•
Since this is an infinite line of charge, it doesn’t matter which location is the origin on
the line of charge
The electric field from each element of charge dq ALWAYS lies in the plane of the
page, assuming that the observation point is also in the plane of the page.
The TOTAL electric field from the line of charge will point perpendicular to the line of
charge
The TOTAL electric field from the line of charge will point parallel to the line of
charge
The Total electric field from the line of change should NOT depend on D.
Electric Field Lines
Vector map of electric field
Direction of field lines indicate local direction of E field (and force on POSITIVE test
charge
Number of lines leaving/ entering a charge proportional to the charge
Field lines BEGIN on POSITIVE charges and END on Negative charges
Density of Field lines proportional to STRENGTH of electric field
Electric Field Lines
Electric Dipole
Where is Electric field strongest?
Weakest?
Electric Field Lines
Where is Electric field Weakest?
Electric Field Lines
In what direction does electric field point at the surface of these conductors?
Note: Field lines from charged conductors reflect the shape of the conductor
Note: Electric field “concentrated” by sharp point of object on left. Like a lightning rod.
Note: What is the E field INSIDE of the conductor in the picture on the right?
I-Clicker Question
Which picture best represents the motion of an electron (negatively charged) as it
passes through the electric field?