• FISIKA DASAR


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    • Abstract: FISIKA DASARListrik MagnetDjati HandokoDepartemen Fisika [email protected], [email protected] Silabus Listrik• Physics for Scientists and Engineers, 6th Edn[1]. (R.A.Serway,J.W.Jewett, Thomson 2004, ISBN 0534408427)

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FISIKA DASAR
Listrik Magnet
Djati Handoko
Departemen Fisika UI
[email protected], [email protected]
08129789507
1
Silabus Listrik
• Physics for Scientists and Engineers, 6th Edn[1]. (R.A.Serway,
J.W.Jewett, Thomson 2004, ISBN 0534408427)
• Medan Listrik:
– Distribusi Muatan Diskrit
– Distribusi Muatan Kontinu
• Potensial Listrik
• Kapasitansi, Dielektrik, dan Energi Elektrostatik
• Arus Listrik
• Rangkaian Arus Searah
2
Silabus Magnet
• Medan Magnetik
• Sumber Medan Magnetik
• Induksi Magnetik
• Magnetisme Dalam Materi
• Rangkaian Arus Bolak Balik
• Persamaan Maxwell dan Gelombang
Elektromagnetik
3
Electric Fields
4
Properties of Electric Charges
• In a series of simple experiments, it was found that there are two
kinds of electric charges, which were given the names positive and
negative by Benjamin Franklin (1706–1790).
• charges of the same sign repel one another and charges with
opposite signs attract one another.
5
Properties of Electric Charges
6
Charging Objects By Induction
Charging a metallic object by induction (that is, the two
objects never touch each other).
(a) A neutral metallic sphere, with equal numbers of positive and
negative charges.
(b) The electrons on the neutral sphere are redistributed when a
charged rubber rod is placed near the sphere.
(c) When the sphere is grounded, some of its electrons leave through
the ground wire.
7
Charging Objects By Induction
(d) When the ground connection is removed, the sphere has excess
positive charge that is non uniformly distributed.
(e) When the rod is removed, the remaining electrons redistribute
uniformly and there is a net uniform distribution of positive charge
on the sphere.
8
Coulomb’s Law
• The electric force:
– is inversely proportional to the square of
the separation r between the particles and
directed along the line joining them;
– is proportional to the product of the
charges q1 and q2 on the two particles;
– is attractive if the charges are of opposite
sign and repulsive if the charges have the
same sign;
– is a conservative force.
9
Coulomb’s Law
10
Some applications
painting static charge
11
Quick Quiz
Object A has a charge of +2 µC, and object B has a charge of +6
µC. Which statement is true about the electric forces on the objects?
– (a) FAB = -3FBA
– (b) FAB = -FBA
– (c) 3FAB = -FBA
– (d) FAB = 3FBA
– (e) FAB = FBA
– (f) 3FAB = FBA
12
example
• Consider three point charges located at the corners of a right triangle
as shown in figure, where q1= q3 = 5.0 µC, q2 =-2.0 µ C, and a =
0.10 m. Find the resultant force exerted on q3.
13
quiz
Dua buah bola bermuatan identik masing-masing memiliki massa 3 x 10-2 kg
digantung dalam keadaan setimbang seperti terlihat pada gambar. Panjang kawat
L = 15 cm dengan sudut θ = 5o. Tentukanlah :
– Besarnya muatan masing-masing bola
– Seandainya temanmu mengajukan masalah ini dengan asumsi kedua muatan
tidak identik. Ia mengklaim bahwa kondisi simetri seperti pada gambar tidak akan
terpenuhi karena muatan tidak sama, sehingga sudut yang dibentuk kawat akan
berbeda. Akibatnya problem yang harus diselesaikan jadi jauh lebih sulit,
bagaimana pendapat kamu
14
The Electric Field
An electric field is said to exist in the region of space around a
charged object (the source charge). When another charged object
(the test charge) enters this electric field, an electric force acts on it.
15
The Electric Field
A small positive test charge qo placed near an object carrying a much
larger positive charge Q experiences an electric field E directed as
shown.
16
The Electric Field
A test charge q0 at point P is a distance r from a
point charge q.
(a) If q is positive, then the force on the test charge is directed away from q.
(b) For the positive source charge, the electric field at P points radially
outward from q.
(c) If q is negative, then the force on the test charge is directed toward q.
(d) For the negative source charge, the electric field at P points radially
inward toward q.
17
The Electric Field
at any point P, the total electric field due to a group of source
charges equals the vector sum of the electric fields of all the charges.
18
example
• A charge q1 = 7.0 µC is located at the
origin, and a second charge
q2 = -5.0 µC is located on the x axis,
0.30 m from the origin. Find the electric
field at the point P, which has
coordinates (0, 0.40) m.
19
Electric Field of a Continuous
Charge Distribution
The electric field at P due to a continuous
charge distribution is the vector sum of the
fields ∆E due to all the elements ∆q of the
charge distribution.
20
• The total electric field at P due to all elements in the charge
distribution is approximately
• Electric field due to a continuous charge distribution
• When performing such calculations, it is convenient to use the
concept of a charge density along with the following notations:
• If the charge is nonuniformly distributed over a volume, surface, or
line, the amounts of charge dq in a small volume, surface, or length
element are
21
Example: The Electric Field Due to a
Charged Rod
• A rod of length l has a uniform positive charge per unit length λ and a
total charge Q. Calculate the electric field at a point P that is located
along the long axis of the rod and a distance a from one end
22
• The field dE at P due to this segment is in the negative x direction
(because the source of the field carries a positive charge), and its
magnitude is
• The total field at P due to all segments of the rod, which are at
different distances from P, is given by equation before, which in this
case becomes
23
Electric Field Lines
• The electric field vector E is tangent to the electric field line at each
point. The line has a direction, indicated by an arrowhead, that is the
same as that of the electric field vector.
• The number of lines per unit area through a surface perpendicular to
the lines is proportional to the magnitude of the electric field in that
region.
Electric field lines penetrating two surfaces.
The magnitude of the field is greater on
surface A than on surface B.
24
rules
25
26
Motion of Charged Particles in a
Uniform Electric Field
• When a particle of charge q and mass m is placed in an electric field
E, the electric force exerted on the charge is qE
• The acceleration of the particle is therefore
27
An Accelerating Positive Charge
• A positive point charge q of mass m is released from rest in a uniform
electric field E directed along the x axis, as shown in figure. Describe
its motion (726).
28
The Cathode Ray Tube
• Electrons leaving the cathode C are accelerated to the anode A. In
addition to accelerating electrons, the electron gun is also used to
focus the beam of electrons, and the plates deflect the beam.
29
quiz
• A small, 2.00-g plastic ball is suspended by a 20.0-cm-long string in a
uniform electric field as shown in figure. If the ball is in equilibrium
when the string makes a 15.0° angle with the vertical, what is the net
charge on the ball?
30


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