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)

(C) (D)

(E)

Charging objects by induction

“Ground” – an infinite source or sink of charge

Note asymmetric charge distribution in sphere. Why?

Note more + charges than negative. Why?

Charges have rearranged again. Why?

Balloon “sticking” to wall.

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?

• 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.

(A) Only 1 statement true (B) two are true (C) three are true (D) only 1 is false (E) none false

Electric Field LinesVector map of electric fieldDirection of field lines indicate local direction of E field (and force on POSITIVE test chargeNumber of lines leaving/ entering a charge proportional to the chargeField lines BEGIN on POSITIVE charges and END on Negative chargesDensity of Field lines proportional to STRENGTH of electric field

Electric Field LinesElectric Dipole

Where is Electric field strongest? Weakest?

Electric Field LinesWhere is Electric field Weakest?

Electric Field LinesIn what direction does electric field point at the surface of these conductors?

Note: Field lines from charged conductors reflect the shape of the conductorNote: 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?