Physics72.1 Laboratory Manual

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PHYSICS 72.1,

LABORATORY MA}{TJAL by'

Rommel C. Gutierrez Maricor N. Soriano Rumelo Amor Marie Ann Michelle Calix

Edmundo Casulla LizaDavtla Michelee Patricio PetetJohn Rodrigo Miguel Yambot

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Fitst Edition, June 2000 Second Edition, Jun e 2001, Edited by: Edmundo Casulla

LizaDavtla Christine Ison Jonathan Palero PeterJohn Roddgo Miguel Yambot

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Policies and guidelines

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EXPERIMENTS

1. Electric field and field potential

1

2. Ohm's law 7

3. Resistors in series and parallel 19 4. Ktrchoff's rules 25 5. Electromagnetic induction 33 6. Introduction to alternating current (ac) circuits 43 7. Optical disk: reflection and refraction 57

8. Image formation using thin lenses 67 References 74

1.

Grading System Laboratory Reports Practical Exam N-ritten Final Exam Recitation, Quizzes, etc

TOTAL

60% 1,5% 1.50

10% 1,00%

Grade Equivalent

>x 92 >x 88 >x 84 >x 80 >x 76 >x

100

Z.

72 >x 68 >x 64 >x 6o >x 50 >x

> > > >

68 +2.50 64 +2.75 60 -+3.00 5o +4'oo > 0 ->5.00

Laboratory Report Guidelines I.

Data sheets (or the manual itself) are collected by the instructor at the end of each experiment, and ate returned during specified periods for wdting the report. II. Laboratory reports are accomplished individualty and only during r.port-*riti.rg sessions. They are collected at the end of these periods. References (textbooks and journals only) are allowed during these sessions.

3.

Genetal Guidelines

I.

If a student misses an experiment, he has to present a medical certificate (in cases where applicable) from the UP Infirmary within.seven (7) days of the absence, or within the first day he is able to come to class. Failure to do so forfeits the student's right to a make-up experiment. Only two experiments are allowed for make-up. II' In the event a student misses the final exam or practical exam, a grade of "INC" is given with the tematk "missed the final exam" or "missed the practical exam." III. A grade of "DRP" or dropped is given upon the initiation of the student, and provided he submits a copy of the dtopping slip to his instructor. The same rule applies to students who file a leave of absence pOA). fV' A grade of "4.0" impJies that the student should retake the course as there is no

v.

A student who

has not submitted at least 4 experiments by the droppingdate automatically be given a failing grade of "5.0" if the student has not dropped.

National Instirute of Physics, Up Diliman

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I}iTRODUCTION The electrostatic force on charge qo due to charge 4 is given by (Coulomb's law):

F-

kq!,,

r

i

per charge qoin moving the charge berween rwo

points

potential difference AZbetween the points: (1

.1)

LVu,

where r is the distance between the charges, i is the unit vector pointing from q to ,q, and the consrant ,€ is 9.0 x 10e N-m2 /cz. The direction of the force on a charge may be determined :sing the law of charges. Like charges repel and ';ilike charges attr^ct.

(unit is N/C).

-Vz-V, -vru =it Ot 40)

where

Q.4)

dl is thepath from A to B.

For a finite path length Ad the magnirude the electric field is given by:

lal=+

The electric field is defined as the electrical :orce per unit charge, or

-tr lr-_

in an electric field, E is called the

of

(1.s)

If a charge is moved ilong a path at right (1.2)

4o

na the case

of the electric field associated with a s:agle source charge Q, the magnitude of the sectric field a distance r away from the charge q :s

angles

ot perpendicular to the field, there is no

work done M=0), since there is no force

component along the path. Then along such p

path,

LVru =Vt -Ve

=Y=g.

(1.6)

4o

E

r =9r =L=\!r?= r Qo q,r'

If

(1.3)

a free charge, 4,, is released in the vicinity :i a stationary soufce charge, it would move .{ong a line of force. Since a free charge moves '- an electric field by the action of the electric iorce, work is done by the field in moving the 'd:arge from one point to another. The work IV

Vu

=Vn'

(1.7)

Hence, the potential is constant along paths peqpendicular to the field lines. Such paths are called equipotential lines (or equipotential surfaces in three dimensions).

oBIECTT\rE To determine the equipotential surfaces in an electrolytic ank and estimate the direction and the snitude of the electric field.

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Institute of Physics, UP Diliman

1.

Electric Field and Field Potential

MATERIALS

Fig. 1.1 The experiment set-up, Two cylindrical electrodes ate immersed in a shallow pool of watet of constant depth. The elecrodes ate Placed at (0r8) and (0,-4).

PROCEDURE

1.

Pour water on the electtolytic tank. Put two disc electodes at coordinates (0,8) and (0,-4). Attach the connectors to the probe, pov/er supply and voltmeter as shown in Fig. 1.1.

4.

of values, instead plot the coordinates

on Graph 1.1 in the data sheet. The symmetry of the gtven electrode

/

configuration allows you to limit the plot to

the first and fouth quadrants. It convenient to make eithet x- or

3.

field

:I

uolt/cm. Show sample calculations the magnitude and draw the E vectors

cm

is

for

y-

on Graph 1.1.

coordinate an integer when locating a point in an equipotential line. Choose the points such that they span the whole area of the tank. Trace the equipotential line fot a potential of 1.0 V.

of the electric

(magnitude and dkection) at the points of intersection of the equipotential Line V(*,1) = 3,0 V 'nth x = 0, 2, 4,6. Get the values of Alby measuring the perpendicular distance ftom each of these points to an adjacent equipotential line and AV from the difference in potential between *re 3.0 V line and this adiacent equipotential line. Represent the electric field vector, -E at these points by arrows using a scale of

2. !7ith the probe tip on the electrolytic tank, determine 5 to 10 coordinates with a potential value of 1.0 V. Do not make a table

Obtain an estimate

5.

in (0, 8) with a long rod oriented peqpendicular to the yaxis. Repeat steps 2 to 4 and Plot Replace the disc electrode

coordinates on Graph 1.2.

Perform step 2 fot potentials of 2.0 V, 3.0 V, 4.0 V, 5.0 V and 6.0 V.

National Institute of Physics, UP Diliman

1. Electric Field and

\-ame:

Date Performed:

Partners:

Date Submitted:

lrsrructor:

Section:

Gruph

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Electric Field and Field Potential for Two Disc Electrodes

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Institute of Physics, UP Diliman

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1. Electric Field and Field Fotential

Graph L.2 Electric Field and Field Potentid for One Disc Electrode and One Rod Electode

Calculations

National Institute of Physics, UP Dilirnan

Physics 72.1

1.

Electric Field and Field Potcrtid

QUESTTONS

1.

The direction of the electdc field is indicated on field lines. \Why are there no directions indicated on equipotential lines?

Use the equipotential lines to explain why the surface charge density Lt each electrode is not uniform.

Use the equipotential lines and associated lines edge of the tank.

+

of force to show that there are excess charges at the

For the electrode configurations in Graphs 1.1 and1,.2, comment on the electric field (a) between the electodes, and (b) near the edges of the electrodes. In what region(s) does the electric field have the greatest intensity? How is this determined from the plot?

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lostin:te of Physics, UP Dilirnan

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Physics, UP Diliman

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INTRODUCTION Ohm's Law states the linear relationship between the voltage ar-rd current of an electrical &cuit that contains resistors only. It is stated in the following way: 'If t])e Empqdture and otbq fiiyical conditions ofa ntewllic confucnr is unclnngd,

The resistance of an ohmic conducting wire is found to be proportional to its length and inversely proportional to its cross-sectional area. Its constant of proportionality is called resistivity of the conductor, p. The SI unit of p is the ohm-meter (O-*).

the ratio oftbe potential dffirence to tbe current is constant."

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This onsant is knovrn to be the resistane of the @ndrctor. Nlarhernatically, Ohm's law may expressed as:

The resistivity, p of any metal varies almost linearly with temperature. It is usually given in tables in tenns of its value pa x 2ffC and the temperature coefficient, o. The produa pao is defined as the slope of th. p vs. T curve. The raistivity at some other temperature T fC), is:

(2.r) AV:IR where AV is the potential difference (also called voltag.) across the metal conductor measured in volts (V), I is the current through the conductor measured in amperes (4, ,nd R is the resistance of the conductor meazured in ohms (O).

Although the definition

Q.2)

p(T)=p,[t+o(T-20)]

of

resistance for nonohmic materials is the same as that for ohmic materials, the resistance R, defined for non-ohmic materials is currentdependent. Nonohmic materials will not give us a linear voltage ns. Errrent behavior.

Q.3)

Table 2.L below shows raistivity values at 200C and temperature coefficients of resistance based on the resistance of some corlmon conductors at

OoC.

German (nickel), silver

Table 2.1Resi$ivities and temperature coefficients of common metals

IoBIECTTVE

To determine the behavior of an ohmic material

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Iostitute of Physics, UP Diliman

as a

function of vol

, current and resistance

2. Ohm's Law

Physics 72.1

MATERIALS materials we will use fot this experiment ate enumerated below and are illustrated in Figure 2.1.. The circuit diagrams in

Variable power supply. Its output voltage

The

is0Vtoabout6V. 2-m wire. This will be our resistor. The

the Procedure makes use of the symbols below.

Multimeter. This

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wire is

serve as the

made of

German-nickel.

voltmeter, ammetef and ohmmeter.

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power supply re s isto r

connectors

Multimeter

voltm eter

Variable Supply Power

am m eter

ohm m eter

2-M Resistance wire Fig 2.1 Equipment used in the experiment.

Fig2.2 Symbols used in the citcuit diagtams.

PROCEDURE Read and undetstand the general instructions experiments.

in the text box below before proceeding with

the

To avoid damage to the meters, always start rilrith the metet on its least sensitive scale. Increase the sensitilty of the meter only as needed fot accurate measurementr and temembet to retuflr the meter to its least sensitive scale before proceeding. (tacfoss" so, voltmetets afe connected patallel to the citcuit element. Voltages afe measured Culents are measured ,,through', so ammeters are connected in series with the circuit element.

Tum off the power supply when not measuring. Before using the ohmmeter to measure the resistance of the resistance wire, always disconnect the tesistance wire ftom the powet supply and othet metefs. A. Variation of voltage with current

1.

the following quantities: the resistance of the 2-m wire using an

Measute

ohmmetet, the room temPerature duting the experiment and the diameter of the wite.

Recotd these values in Data Table 2.1. Perfotm 5 trials in measuring the room temperature and the diameter of the wire.

National Institute of Physics, UP Diliman

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