Download Concept Question: 5 Equal Charges

Concept Question: 5
Equal Charges
Six equal positive charges q sit at the vertices of a
regular hexagon with sides of length R. We remove
the bottom charge. The electric field at the center of
the hexagon (point P) is:
 2kq
1. E  2 ĵ
R
 kq
3. E  2 ĵ
R

2kq
2. E   2 ĵ
R

kq
4. E   2 ĵ
R

5. E  0
1
Concept Question Answer: 5 Equal
Charges
Answer 4
4.

kq
E 2
R
jĵ
E fields of the side pairs cancel (symmetry)
E at center due only to top charge (R away)
Field points downward
Alternatively:
“Added
Added negative charge”
charge at bottom
R away, pulls field down
2
Concept Question: Field Lines
Electric field lines show:
1 Directions of forces that exist
1.
e ist in space at all
times.
2 Directions in which positive charges on those
2.
lines will accelerate.
3 Paths that charges will follow
3.
follow.
4. More than one of the above.
5 I don’t
5.
d ’t know
k
.
3
Concept Question Answer: Field
Lines
Answer: 2
2. Directions positive charges
accelerate.
NOTE: This is different than flow lines (3).
g field lines.
Particles do NOT move along
(1) is not correct because we don’t know
sign of charge so we don’t know direction
of force
4
Concept Question: Electric Field
Two charged objects are placed on a line as shown below.
The magnitude of the negative charge on the right is greater
g
of the p
positive charge
g on the left,, qR  qL .
than the magnitude
Other than at infinity, where is the electric field zero?
1.
2.
3.
4.
5.
Between the two charged objects.
To the right of the charged object on the right.
To the left of the charged object on the left.
The electric field is nowhere zero.
Not enough info – need to know which is positive.
5
Concept Question Answer: Electric
Field
Answer: 3. To the left of the positively charged object on the left
http://web.mit.edu/viz/EM/visualizations/electrostatics/ElectricFieldConfigurations/pcharges/pcharges.htm
Between: field points from positively charged object to
negatively charged object
On right: field is dominated by negatively charged object
On left: electric field due to close smaller positively charged
object will cancel electric field due to further larger negatively
charged object.
6