Laboratory session in Physics II subject for September 2016-January 2017 semester in Yachay Tech University (Ecuador). Topic covered: electricity, magnetism Based on Bruna Regalado's work

1. GUIDE FOR PRACTICE 2:
ELECTROSTATICS AND MAGNETOSTATICS
1. CONTENT:
Electrostatics
a-.) Electric charges
b-.) Coulomb's Law
Magnetism
a-.) Definition of magnetism
b-.) Definition of magnet
c-.) Types and Uses
Electrical circuits:
Ohm's law
a-.) Current and Resistance
b-.) Measurements with the multimeter
DC circuits
a-.) Electromotive force (fem)
b-.) Combination of resistors in series and parallel
LEARNING OBJECTIVES
1-.) Consider the types of electrical charges in the world.
2-.)Knowing the physical phenomenon of magnetism.
3-.) Knowing the magnets and experimentally determine its poles.
2-.)Make measurements of voltage, current and resistance with the multimeter.
3-.) Combining resistors in series and in parallel and obtain the equivalent resistance.
4-.) Knowing Ohm’s law and Kirchhoff’s laws.
2. THEORETICAL BASICS:
One of the fundamental forces of nature is electromagnetic, which is between charged particles.
When loads are quiescent, only the force due to the electric field is observed. If loads are
moving, also the force due to the magnetic field is observed.
Electrostatics
Electric charges
In the eighteenth century Benjamin Franklin determined that there are two types of electric
charges, a positive (proton p +) and a negative (e electron), and that the same sign charges repel
and different signs attract, depending on which patterns established as glass (+) and plastic (-).
To know if a body is electrically charged electroscope is often used, which can quickly raise or
lower the burden of an object by charge separation phenomenon of induction.
Coulomb's law:
The magnitude of each of the electrical forces interacting two point charges q1 and q2 at rest is
directly proportional to the product of the magnitude of both charges and inversely proportional
to the square of the distance r that separates and has the direction of the line that unites them.
Fe=Ke∙q1∙q2/r2
PHYSICS II
LABORATORY

2. Being constant Coulomb Ke=1/(4πε0)=8,9876∙109
N∙m2
/C2
y ε0=8,8542∙10-12
C2
/N∙m2
the
vacuum permittivity. The charging unit (e) smallest known in nature is the charge of an
electron (-e) or a proton (+ e), with a magnitude of e=1,60218∙10-19
C.Therefore, a load of 1C
= 6,24 ∙ 1018
e-
o p+
(in 1 cm3
Copper there are about 1023
e-
free). However, despite having the
same charge, the mass of 1 e-
=9,1094 ∙10-31
Kg and mass 1 p+
=1,67262 ∙10-27
Kg.It is known
that the hydrogen atom is the simplest of the chemical elements, possessing only 1 e-
and 1 p+
,
separated by a distance of 5,3 ∙10-11
m.
MAGNETISM
The name comes from the Greek magnetism Magnesia province, where the largest deposits of
magnetite (Fe3O4), with marked mineral magnetic properties. In Greek civilization and
magnetism he was known, but it was not until the work of James Clerk Maxwell when science
"understand" the whole phenomenon. Its famous four equations, originally were twenty, and
managed to synthesize in electromagnetic theory known experimental results of other
researchers, such as Coulomb, Gauss, Faraday and Ampere.
Previous notions
It is called magnetism to property that have some bodies, called magnets, to exert attraction
on other bodies containing iron. It is a phenomenon of physical type. Magnetism to occur
there must be moving charges because the magnetic properties occur by movements of the
electrons, which are each a small magnet, which are located in such a way (in the same
direction) which combine their effects.
The magnetic properties are more pronounced at the ends of the magnet, which are called
magnetic poles, North (N) pole and South (S) pole. Just as the electric charges repel and
attract other magnets that are close by like poles repel and if approaching from opposite poles
attract. It is impossible to isolate a single magnetic pole, so that if a magnet is split in two,
each piece again be a north pole and one south.
In speaking of magnetism called a vector magnetic field B represented by its field lines so that
at each point in space the field is tangent to these lines. The fact that the magnetic poles never
be given separately means that the field lines are always closed, leaving the North Pole and
the South Pole entering (Figure 1).
It is called magnetic field to the portion of space,
where forces on moving charges are exercised,
because of this. When a piece of iron, a magnet or
current thread are placed in an area where there is a
field are subjected a force tending to orient in a
certain way.
Figure 1: Magneticfieldlines.
Magneticfieldlines
The magnetic field lines allow roughly estimated the existing magnetic field at a given point,
taking into account the following characteristics:
• The magnetic field lines are always closed loops that run north to south outside the magnet
and from south to north inside the magnet
• The magnetic loops never intersect
• The magnetic lines of different magnets attract and repel each other: The lines in the same
direction attract and repel the opposite direction

3. • Because moving loads behave like magnets (produce magnetic fields), the effect of
magnetism may be due to electron flow (electric current) as in the case of a magnet and is
independent of the medium.
Uses magnets
There are natural magnets, such as magnetite or triiron tetroxide; and other artificial, that man
has created. The magnets are used to achieve door openings for magnetic boards, pin
cushions, toys; It is a very useful application of the magnet, the compass, which consists of a
box containing inside a needle that moves in free form, but that is magnetized, and therefore
their orientation is always north-south. The power of attraction of the magnetized bodies is
greater at the ends or poles. The Earth acts like a giant magnet, it attracts the bodies that are
upon it by the force of gravity, in this the North Pole and the South Pole (Figure 2) are also
recognized. Similarly, they are called magnetism, phenomena that are caused by some kind of
electrical currents type.
Figure 2: Magnetic poles on Earth
ELECTRICAL CIRCUITS:
Ohm's law
Ohm relates the voltage, current and resistance: current in a circuit is directly proportional
to the voltage across the circuit printed, and is inversely proportional to the resistance of the
circuit. Thatis to say:
Current
And electric current in a conductor is defined as I=dQ/dt, wheredQIt is charge passing through
a conductor cross section in a time intervaldt.The unit in the S.I. for current is Ampere, where
1 A= 1C/s Electric current is defined as the movement of the positive charges, that is, the
current direction is opposite to the movement of e-
, meaning that goes from positive to
negative.
Resistance
The resistance R of a conductor is defined as R=ΔV/I (Ley de Ohm),whereΔV is the potential
difference across it in I is the current leads. The SI unit for resistance is volts per ampere,
which is defined as 1 ohm (Ω); that is to say: 1 Ω= 1 V/A.For an uniform material with cross-
sectional area A and length L, the resistance across the length L block is R= ρ∙L/A,whereρit is
the resistivity of the material. To know the value of a resistor used the following color code:

4. Figure 3: color code to determine the values of the resistors 4 and 5 bands.
Measurements with the multimeter
• To measure the voltage or voltage drop across a resistor is done by selecting the option
voltmeter and measuring in parallel.
• To measure the current through a resistor is selecting and measuring ammeter in series.
• To measure a resistance must first remove the circuit voltage or opening it to not pass
current, and selecting ohmmeter measured in parallel.
• That is, that to measure the potential difference is not required to open the circuit while
measuring the electrical current must open the circuit to incorporate the ammeter.
DC circuits
Electromotive force
For there to be an electric current in a closed circuit must be a battery or power supply
electromotive force fem a potential difference (figure 4). The battery femε is the maximum
voltage that it can supply across its terminals. Since a battery is made of material, there is a
flow resistance of the loads within the same. This resistance is called internal resistance r. The
potential difference is supplied battery ΔV=ε-I∙r. The fem of a battery is equal to voltage
across its terminals when the current is zero. That is, the emf is equivalent to the open circuit
voltage of the battery.
Figure 4: Diagram of a circuit of a source of fem, internal resistance r, connected to an
external resistor, resistance R.

5. Resistors in series and parallel (figure 5)
• The equivalent resistance of a set of resistors connected in a series combination is:
Req= R1+R2+R3+…, in this combination it is kept constant the current flowing.
• The equivalent resistance of a set of resistors connected in a parallel combination is based on
the correspondence 1/Req=1/R1+1/R2+1/R3+…, in this combination remains constant voltage
in the circuit.
Figure 5: equivalent Resistors: serial (left) and parallel (right)
3. LABORATORY MATERIALS:
Panel pins 4 mm
Potentiometer (P1) 250Ω, 4w, G3
Switch, G1
Resistance. 47Ω, 1w, G1
Resistance. 100Ω, 1w, G1
Resistance. 470Ω, 1w, G1
Resistance. 1 k, 1w, G1
Graphite resistance. 4.7 KQ, 1W, G1
Electroscope metal indicator
Resistance. 10 k, 1W, G1
Resistance. 47 KQ, 1W, G1
DC power source from 0 to 12V, 2A / AC: 6V,
12V, 5A
Multimeter
Support bar, L = 100mm
Magnet, d = 8mm, L = 60mm
Polycarbonate plate
Pocket compass
Sprinkler iron powder
Scissors
4. EXPERIENCES:
Activity 1: Determining the sign of electric charges by standards established by
Benjamin Franklin
1) Place in the inn laboratory on a small white sheet pieces: paper (white sheet), aluminum
foil, foam flex, ground cork, others. Take the glass rod (Plexiglas) and rub with the cloth, then
move it closer to each of the items you have on the counter.
2.) Perform again the experience but with the plastic bar.
Activity 2: Determination of magnetic field lines
1.) Place the magnet on the counter 60mm laboratory. This hold the polycarbonate plate or a
sheet of paper, spray at low altitude and on the plate, and gently iron powder. (Note: red polo
represents the north).
2.) Note the orientation of the magnetic field lines and identify the respective poles.
Note: If you want to get a better distribution of iron powder carefully tap the plate or white
sheet.
Activity 3: Determination of the orientation of the needle of a compass by using a
magnet
1.) Place the magnet 60mm (standard) on the counter of the laboratory.
2.) Take the pocket compass and describe a circle around the magnet.
Activity 4: Identification of the poles of a magnet using the magnet pattern
1.) Place the magnet 60mm (standard) on the counter of the laboratory.

6. 2.) Take the magnet 50mm and move it near the magnet pattern.
3-.) Identify the poles observing the attraction or repulsion present.
Activity 5: Obtaining the resistance value by color coding
1.) Take several carbon resistors and using color code indicates its value.
2.) Check with the multimeter the value obtained.
Activity 6: Measuring the current through a simple resistive circuit in two ways:
using the multimeter as ammeter and voltmeter-ohmmeter
1.) Install a circuit with 2 resistors in series and a potentiometer (P1) (variable resistance) and
feed it with a voltage 8 V. Indicate current value supplied.
2.) With the Meter measures the voltage values in every part of the electrical circuit.
3.) By Ohm's Law to determine the value of the currents flowing through the circuit.
Activity 7: Combination of resistors in series and parallel
1.) Riding tablet Tests 3 resistors in series and measure the equivalent resistance.
2.) Perform installation again but with parallel resistors.
5. EVALUATION OF DATA
ACTIVITY 1
Indicate what happens to each of the items on the counter and observed what happens.
Indicate the sign of the charge of each element.
ACTIVITY 3
Draw a circle on the orientation of the compass needle indicating the respective poles.
ACTIVITY 4
According to the type of force experienced determine how far a greater or lesser attraction or
repulsion feels.
ACTIVITY 5
Complete thefollowingtable:
R (theoretical
value)
Color of
stripes
Tolerance Resistance (with error)
Specificquestions
1.) For the hydrogen atom, compare the electrical and gravitational force between the p +
and e-
, knowing that the gravitational constant is G = 6.67x10-11
Nm2
/ kg2
2.) What is a eV and what physical quantity is measured?
3-.) Analyze and interpret the configuration of magnets described below, where N is the
north pole of the magnet, S is the South Pole between these two magnets and height h, a

7. piece of iron with a smaller height is placed at the of magnets. Configuration: N-S-iron-S-
N.
4.) In the above configuration, you consider what can be achieved by a magnet with two
equal poles at their ends? If yes of what use would this magnet?
5.) What advantages does placing resistors in series or parallel?
6.) According to the definition of resistivity of a material influences how the length of the
conductor for selecting a certain resistance.
7.) What is the relationship between voltage, current if the voltage is increased or
decreased? Would such increase or decrease how it affects the resistance?
5-. EXTRA HELP LITERATURE
• Jerry D. Wilson, Anthony J. Buffa and Bo Lou. Physical. Pearson Prentice Hall, 2007
• Paul A. Tipler and Gene Mosca. Physics for Science and Technology, 10th edition Editorial
Reverte, 2007
• Paul G. Hewitt. Conceptual Physics, 11th edition. Pearson Education, 2009
• Raymond A. and C. VuilleSerway. College physics. Cengage Learning, 2011
• Richard P. Feynman, Robert B. Leighton, and Matthew L. Sands. The Feynman Lectures on
Physics "vol. 1. Addison Wesley, 1989
Links:
Electroscope
https://www.youtube.com/watch?v=mj3YduHNDmg
As use a breadboard
https://www.youtube.com/watch?v=f9LaxI34RK4
Using multimeter (basic)
https://www.youtube.com/watch?v=dCW0v6am_U0
28. The Mechanical Universe – Static
https://www.youtube.com/watch?v=TN3jw9HFyXY&list=PLbVU10RMo-
a707GUomDWzPY0I40JyveLt&index=28
31. The Mechanical Universe - Voltage, power, strength
https://www.youtube.com/watch?v=2w3HY0UXKBI&list=PLbVU10RMo-
a707GUomDWzPY0I40JyveLt&index=31
Introduction to the magnetic field
https://www.youtube.com/watch?v=MZVKEZsUVpo
What is magnetism?
https://www.youtube.com/watch?v=KvhpTgmvMRI
The great Gauss and magnetic field
https://www.youtube.com/watch?v=mxZ9OJsO6PI