Concept Question: Dipole in NonUniform Field
E
A dipole sits in a non-uniform
electric field E
Due to the electric field this dipole will
feel:
1.
1
2.
3.
4
4.
fforce but
b t no torque
t
no force but a torque
both a force and a torque
neither a force nor a torque
1
Concept Question Answer: NonUniform Field
E
Answer: 3. both force and torque
Because the field is non-uniform, the forces on
the two equal but opposite point charges do
not cancel.
As always
always, the dipole wants to rotate to align
with the field – there is a torque on the dipole
as well
2
Concept
p Question
Q
Electric Field of a Rod
A rod of length L lies along the
xx-axis
axis with its left end at the
origin. The rod has a uniform
charge density λ. Which of the
f ll i expressions
following
i
b
bestt
describes the electric field at
the point P
x L

 dx
î
1. E(P)   
3
(x  d)
x0
x L

 dx
î
4. E(P)  
2
(x  d)
x0
x L

 dx
î
2. E(P)  
3
(x  d)
x0

5. E(P)  
xx L

 dx
d
î
3. E(P)   
2
(x

d)
x0

6. E(P) 
L
(d  x)
L
(d  x)2
2
î
î

L
7. E(P)   2 î
d

L
8. E(P)  2 î
d
9 None of the above.
9.
above
3
Concept Question Electric Field of a Rod:
Answer
A rod of length L lies along the
x-axis
i with
i h iits lleft
f end
d at the
h
origin. The rod has a uniform
charge
g density
y λ. Which of the
following expressions best
describes the electric field at
the point P

5. E(P)  
L
(d  x)2
î
4
Concept
p Question
Q
Electric Field of a Ring
g
A uniformly charged ring of radius
a has
h ttotal
t l charge
h
Q
Q. Which
Whi h off th
the
following expressions best
describes the electric field at the
point P located at the center of the
ring?
 2 

 ad
1. E(P)   
î
3
a
 00
 2

 ad
î
2. E(P)  
3
a
 0

Q
3. E(P)   2 î
a


Q
4. E(P)   2 î
a


5. E(P)  0
5
Concept Question Electric Field of a Ring:
Answer
A uniformly charged ring of radius
a has
h ttotal
t l charge
h
Q
Q. Which
Whi h off th
the
following expressions best
describes the electric field at the
point P located at the center of the
ring?


5. E(P)  0
6