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Salman bin Abdel-Aziz University
104 Phys
Faculty of Science in Al-Afaj
Electricity and Magnetism + Optics
Department of Physics
Revision
Electricity and Magnetism
CHAPTE R 23 – Electric fields
‫ ولكنها مجرد نماذج ألسئلة االختبارات للتدريب عليها‬،‫هذه المراجعة ليست ملخص للمادة وال يكتفى بها‬
This revision is not a compendium for the subject and not enough, it is
only a model for the exam's questions for training.
You may need to physical constants of the following:
1) The Coulomb constant
[ke = 9 × 109 N.m2/C2]
3) The permittivity of free space
[ = 8.85 × 10-12 C2/N.m2]
4) The charge of the electron is
[e = - 1.6 × 10-19 C]
5) The charge of the proton is
[e = 1.6 × 10-19 C]
6) The charge of the neutron is
[e = 0 C]
7) The mass of the electron is
[me = 9.10 × 10-31 kg]
8) The mass of the proton is
[mp = 1.67 × 10-27 kg]
9) The mass of the neutron is
[mn = 1.67 × 10-27 kg]
(Q1) Which statement is true (√) and which is false (×) of the following:
(Q1) Correct the mistakes in the following sentences if found:
) It was found that there are two kinds of electric charges, which were given the names positive and
negative by Benjamin Franklin (1706-1790).
) There are two kinds of charges in nature; charges of opposite sign attract one another and charges of the
same sign repel one another.
) Charges of the same sign repel one another and charges with opposite signs attract one another.
) Total charge in an isolated system is conserved.
) Electric charge is always conserved
) Electric charges are quantized
) The electric charge q is said to be quantized.
) All substances consists of electric charges
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) Millikan discovered that electric charge always occurs as some integral multiple of a fundamental
amount of charge e.
) The smallest unit of charge e known in nature is the charge on an electron (- e) or a proton (+ e) and has
a magnitude e = 1.6 × 10-19 C
) Electron has negative charge wile protons has positive charge.
) Neutron has no charge (neutralized).
) Electrical conductors are materials in which some of the electrons are free electrons1 that are not bound
to atoms and can move relatively freely through the material.
) Electrical insulators are materials in which all electrons are bound to atoms and cannot move freely
through the material.
) Materials such as glass, rubber, and wood fall into the category of electrical insulators.
) Semiconductors are a third class of materials, and their electrical properties are somewhere between
those of insulators and those of conductors.
) Silicon and germanium are well-known examples of semiconductors commonly used in the fabrication
of a variety of electronic chips used in computers, cellular telephones, and stereo systems.
) The electrical properties of semiconductors can be changed over many orders of magnitude by the
addition of controlled amounts of certain atoms to the materials.
) The electric force between two stationary charged particles is inversely proportional to the square of the
separation r between the particles and directed along the line joining them
) The electric force between two stationary charged particles is proportional to the product of the charges
q1 and q2 on the two particles.
) The electric force between two stationary charged particles is attractive if the charges are of opposite
sign and repulsive if the charges have the same sign
) The electric force between two stationary charged particles is a conservative force.
) The SI unit of charge is the coulomb (C).
) 1 C (Coulomb) of charge is approximately equal to the charge of 6.24 × 1018 electrons or protons.
) The number of free electrons in 1 cm3 of copper is on the order of 1023.
) Coulomb's constant has no units.
) The constant ke can be written in the form [ke = 1/4].
) The value of the Coulomb constant depends on the choice of units.
) An electric field exists at a point if a test charge at that point experiences an electric force.
) The electric field vector E has the SI units of newtons per coulomb (N/C).
We can interpret the electric field as a measure of the rate of change with position of the electric potential .
) Electric field lines are the curved lines that are parallel to the electric field vector at any point in space,
and they were introduced by Michael Faraday.
) The electric force between two point charges is sometimes called the Coulomb force.
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(Q2) Choose the correct answer:
) Object A has a charge of +2 C, and object B has a charge of +6 C. 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
) A piece of metal has a charge of -1.6 × 10-16 C, so it should contain
a) 1000 electrons
b) 100 electrons
c) 10 electrons
d) 1 electron
) 1 C of charge has a number of electrons or protons about
a) 6.24 × 1018
b) 1.6 × 10-19
c) 1
d) 16
c) positive or negative
d) all are true
c) positive
d) negative
) The electric charge q is always
a) conserved
b) quantized
) The electric charge q is always
a) conserved
b) static
(Q3) Complete the missed words:
) …………………. is a scalar characteristic of an electric field, independent of any charges that may be
placed in the field .
) ………………………. are materials in which some of the electrons are free electrons1 that are not
bound to atoms and can move relatively freely through the material
) …………………….. are materials in which all electrons are bound to atoms and cannot move freely
through the material.
) ……………………… are a third class of materials, and their electrical properties are somewhere
between those of insulators and those of conductors.
) ………………………. at a point in space is defined as the electric force Fe acting on a positive test
charge q0 placed at that point divided by the test charge.
) ……………………………. are the curved lines that are parallel to the electric field vector at any point
in space, and they were introduced by Michael Faraday.
) Charges of the same sign …………………… one another and charges with opposite signs
………………… one another.
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) The electric force between two point charges is sometimes called the ……………………….. force.
* Choose the missed words from the following:
(repel – Metals – Semiconductors – attract – insulators (dielectrics) – charges – electric – positive –
negative – Coulomb)
(Q4) What is the scientific reason of the following:
1) If you rub an inflated balloon against your hair, the two materials attract each other.
This is because the speed of light in medium v is always less than the speed of light in vacuum c.
(Q5) State the following laws:
1) Coulomb’s law
(Q6) Essay questions:
) Write briefly about Coulomb's law.
(Q7) Solve the following problems
) If two small objects are suspended by thin strings and then electrically charged, they may repel each
other and hang apart. If each charge is 2×10-4 C and the distance between them is 10 cm, calculate the
repulsion force between the two charged objects.
) The electron and proton of a hydrogen atom are separated (on the average) by a distance of
approximately 5.3 × 10-11 m. Compare between the magnitudes of the electric force and the gravitational
force between the two particles.
(Q8) Define the following terms
1) Metals
2) Electric potential
4) The electric field vector E
3) Electrostatic force
5) The electric field lines
(Q9) Mention the measurement units of the following terms:
5) Electric charge
7) Light velocity
11) The electric field vector
8) Electric potential
12) Electric energy
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9) Electrostatic force
Q10): Mention the measurement units of the following terms:
Quantity Electric potential
electric energy
permittivity
electric
field
Electrostatic
force
Electric
charge
Unit
(Q11) Give the scientific terms of the following definitions:
) The electric force Fe acting on a positive test charge q0 placed at that point divided by the test charge.
) The curved lines that are parallel to the electric field vector at any point in space, and they were
introduced by Michael Faraday.
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