Transcript Chapter 22

CHAPTER-22
Electric Field
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Ch 22-2 Electric Field
 Field: Region of space characterized by
a physical property
 Scalar physical property- scalar field;
vector physical property- vector field
 The Electric Field characteristics:
Exerts force on a positive test charge
 Electric field is due to a charge and
surrounds it
 Direction of E( given by arrow head):
away from a positive charge and
towards a negative charge
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Ch 22-3 Electric Field
Lines
 Space around charge filled with
lines of force or electric field
lines
 Direction of E-field lines or
direction of the tangent to a
curved field line gives the
direction of E at that point.
 Number of E-field lines per unit
area , measured in a planeto the
lines, is proportional to the
magnitude of E.
 Closer lines, larger E and farther
the lines, the weaker is E field
 Parallel E field lines means
uniform E-field
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Ch 22-4 Electric Field Due to a Point Charge
Electric Field
due to a point
charge
E
qo P
E=F/q0=kq2/r2

 E-field due to
sum of Charges:
Enet=Ei
=E1+E2+E3+….
q
r
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Ch 22-4 Electric Field Due to a Point
Charge
 Field between three
charges:
 Zero Net Field location:
 For opposite charges ,
it is on the sides of
the charges and nearer
to weaker charge
 For similar charges , it
is between the charges
and nearer to weaker
charge
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Ch 22-5 Electric Field Due to a
Electric Dipole
 Electric Field Due to a
Electric Dipole
 Ed=2kqd/z3= (1/20) p/z3
 where p is electric dipole
moment given by:
 p=qd
 direction of p is taken
from negative end to
positive end of dipole
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Ch 22-8 A Point Charge in an Electric Field
The electrostatic force
F on a charge q in an
external field E is in
the direction of E for
positive charge and in
opposite direction for
negative charge
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Ch 22-9 A Dipole in an Electric Field
 Net torque on the dipole
= p xE =pEsin
 Negative torque for clockwise
rotation
=- pEsin
 Positive torque for
counterclockwise rotation
=pEsin
 Potential Energy U of a Dipole (U90=0)


F+
Fx-axis
U=-W=- 90d=  90pEsin  d
U=-p Ecos = -p.E
Umin=-pE (=0); Umax=+pE(=180);
 W=-U=-(Uf-Ui)
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Suggested problems Chapter 22
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