Download القسم: العلوم الطبية التطبيقية

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 27 – Electric current and resistance
‫ 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]
2) The permittivity of free space
-12 C2/N.m2]
3) The charge of the electron is
[e = - 1.6 × 10-19 C]
4) The charge of the proton is
[e = 1.6 × 10-19 C]
5) The charge of the neutron is
[e = 0 C]
6) The mass of the electron is
[me = 9.10 × 10-31 kg]
7) The mass of the proton is
[mp = 1.67 × 10-27 kg]
8) 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:
1) It is conventional to assign to the current the same direction as the flow of positive charge.
2) The direction of the current is the direction in which positive charges flow when free to do so.
3) The direction of the current is opposite the direction of flow of electrons.
4) The SI unit of current is the ampere (A).
5) It is common to refer to a moving charge (positive or negative) as a mobile charge carrier.
6) The mobile charge carriers in a metal are electrons.
1
7) The speed of the charge carriers vd is an average speed called the drift speed.
8) A current density J and an electric field E are established in a conductor whenever a potential
difference is maintained across the conductor.
9( The electric current depends on the cross sectional area of the conductor while the current density
doesn’t.
(Q2) Choose the correct answer:
1) 1 A (Ampere) is equivalent to:
a) 1 C/s
b) 1 s/C
c) 1 C×s
d) 1/C×s
c) 1×10-9 A
d) 1×10-12 A
b) 1×10-6 A
c) 1×10-9 A
d) 1×10-12 A
b) 1 A/V
c) 1 V×A
d) 1/V×A
c) 1000 
d) 1×106 
2) 1 A (micro Ampere) equals:
a) 1×10-3 A
b) 1×10-6 A
3) 1 mA (milli Ampere) equals:
a) 1×10-3 A
4) 1  (ohm) is equivalent to:
a) 1 V/A
5) 1 k (kilo ohm) is equivalent to:
a) 10 
b) 100 
6) The electric current in a conductor is affected by:
a) the charge carrier density
b) the drift velocity
c) the cross-sectional area (A) of the conductor
d) All previous are correct
(Q3) Complete the missed words:
1) The electric …………………… is the rate at which charge flows through the surface of a conductor.
2
2) The electric current is ……………….. proportional to the cross sectional area of the condcutor.
3). The ………………… in the conductor is defined as the current per unit area.
* Choose the missed words from the following: (charge – current – current density – linearly – inversely)
(Q4) What is the scientific reason of the following:
1) Increasing in the temperature of the conductor when electric current passes through this conductor.
The energy transferred from the electrons to the metal atoms during collisions causes an increase
in the vibrational energy of the atoms and a corresponding increase in the temperature of the
conductor.
(Q5) State the following laws:
1) Ohm's law
(Q6) Define the following terms
1) Electric current (I)
2) Current density (J)
3) Resistance (R)
(Q7) Mention the measurement units of the following terms:
1) The electric current (I)
2) Current density (J)
3) Resistance (R)
(Q8) Give the scientific terms of the following definitions:
) The rate of flow of charge through some region of space. (electric current).
) The number of mobile charge carriers per unit volume. (The charge carrier density
3