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PHYSICS & ASTRONOMY
DEPARTMENT
The City University of New York COLLEGE OF STATEN ISLAND
Department of Physics & Astronomy
PHY 161
PHYSICS LABORATORY MANUAL
PHYSICS LABORATORY EXT 2978, 4N-214/4N- 215
When entering the laboratory premises you are entering a working professional environment therefore, you are expected to adhere to the following rules:
Food or drinks are not allowed in the laboratory.
The use of cell phones or music players is not permitted.
Behave in a professional and respectful manner towards your instructor, the technical staff and your fellow students.
Punctuality is critical. Arrive on time to each laboratory session or equipment may be removed from your workbench. Punctuality is factored into your grade.
Computers are for experiment use only such as collecting, analyzing and printing data. Do not save any data or modifications made to the experiment templates. If needed, save it to a thumb/flash drive. Web surfing, reading e-mail, playing games, streaming music/videos and printing work from other classes are not allowed.
Laboratory reports must be submitted as soon as you enter the laboratory room; otherwise, points will be deducted for lateness.
Bring a scientific calculator, a notebook and pen/pencil for each laboratory session.
Your laboratory partner and you are responsible for the equipment and workbench you use during an experiment. Please handle equipment with care, do not make any markings or write on any piece of equipment or on your workbench. Being responsible on the handling of equipment and caring for your work station is also factored into your grade.
Return or leave equipment as it was given to you when the laboratory session started. Be mindful that students from other laboratory sections use the same equipment and work stations; please cooperate to maintain everything in working conditions.
After completing an experiment and before leaving the premises check that your workbench is clean and clutter free, push in your chair and either log-off or re-start the computer.
Be sure to take all your belongings, the laboratory is not responsible for any lost items.
Your cooperation in abiding by these rules will be highly appreciated.
Thank You. The Physics Laboratory Staff
LAB WORK 1
LABWORK 1 | 2 PHY 161
For isolated point charges, the equipotential surfaces are spheres, whereas the electric field lines are straight lines (Fig. 1).
Fig.1. Two dimensional presentation of electric field lines (red and blue arrows) and equipotential surfaces (black dotted circles) of isolated positive and isolated negative charges.
For assemblies of point charges and non-point charges, equipotential surfaces and electric field lines have more complex shapes, e.g. see Figs. 2 and 3.
Fig.2. Two dimensional presentation of electric field lines and equipotential lines of positive and negative charges placed at a short distance one from another. Two points a and b between which strength of electric field is measured are shown. The distance d (^) ab is much shorter than total length of the electric field line.
+ -
Equipotential Lines
Electric Field Lines
-^ +
Equipotential lines
Electric
EQUIPOTENTIAL AND ELECTRIC FIELD LINES
PHY 161 LAB WORK 1 | 3
Fig.3. Two dimensional presentation of electric field lines and equipotential lines of two oppositely charged parallel plates. The uniform electric field between the plates is shown by straight parallel electric field lines
The electric field between two oppositely charged parallel plates placed at a distance much smaller than the size of the plates can be considered as uniform (Fig. 3). Note that the electric field in the areas close to the edges of the plates is not anymore uniform. For uniform electric field, there is a simple relation between the strength of electric field E and the potential difference Vab between points a and b lying on one and the same electric field line (Eq. 4):
𝐸𝐸 = −
where dab is the distance between points a and b. Although this formula is not strictly correct for non-uniform electric field, it can be used for estimation of strength of electric fields of any configuration (Fig. 2). In this case, however, the distance d (^) ab must be much less than the total length of the electric field line. Electric field can be created freely only in non-conductive media, e.g. in vacuum, air, or in insulating materials like glass or water. Electric field does not penetrate inside conductors. Thus, inside conductive materials electric field is zero. It is also true for closed hollow conductive objects, e.g. closed metal box, or closed metal cage. Since the electric field is zero, the electric potential inside conductors and conductive hollow objects is constant (Fig 4).
Fig. 4. Equipotential lines and electric field lines around and inside a conductive box. Surface of this box is at a potential V. Potential in every point inside the box is also at a voltage V. The electric field inside the box is zero (no electric field lines).
- - - - - - - - - - - - - - - - - - - - - -
Equipotential lines
Electric field lines
+ + + + + + + + + + + + + + + + +
- - - - - - - - - - - - - -
V1 (^) V2 V3 (^) V4 V5 V6 V
V
+ + + + + + + + + + + +
EQUIPOTENTIAL AND ELECTRIC FIELD LINES
PHY 161 LAB WORK 1 | 5
Experimental Procedure and Calculations
Fig. 6. Configurations of charged metal electrodes on conductive paper: (a) two point charges, (b) two parallel plates, (c) closed conductive surface.
(a) (b) (c)
LAB WORK 1
LABWORK 1 | 6 PHY 161
Questions
LAB WORK 2
LAB WORK 2 | 2 PHY
(a) (b) Fig. 1. (a) Voltage applied to a conductor as a function of the induced current for an ohmic conductor. Slope of this dependence calculated as the change of voltage V divided by the corresponding change of current I equals resistance R of this conductor: R = V/ I. (b) Non-ohmic conductors may exhibit complex non-linear dependences of voltage versus current.
The ability of moving electrons to maneuver through a conducting material depends on the physical parameters of this material and on its temperature. Heating results in thermal agitation of moving electrons and atoms in the conductor. This agitation retards the directional motion of electrons and, consequently, increases resistance of the conductor. The current flow itself can increase temperature considerably: the greater the current in a conductor the higher its temperature. The actual dependence of resistance on temperature is a characteristic of the conducting material. It is measured by so-called temperature coefficient of resistivity α. This coefficient may be positive or negative and therefore the resistance of some conductors increases with temperature, whereas it decreases for the others. For instance, for tungsten α = +4.5×10- °C-1, for carbon (graphite) α = -5×10-4^ °C-1. The change of resistance with temperature is given by the following formula (Eq. 4): 𝑅(𝑇) = 𝑅𝑅𝑇[1 + 𝛼(𝑇 − 𝑇𝑅𝑇)] (4) where R ( T ) is the resistance at temperature T ; TRT is room temperature (usually 20°C) and RRT is the resistance at room temperature.
Apparatus
Variable DC power supply Ammeter (Digital Multimeter set to “mA” DC) Voltmeter (Digital Multimeter set to “V” DC) Tubular power rated resistor (100Ω) Tungsten filament lamp (60W) Carbon filament lamp (32cp) Lamp socket
I slope R V
y=mxm=100.5+/-0.
I
V
OHM’S LAW AND RESISTANCE
PHY 161 LAB WORK 2 | 3
Connecting wires Knife switch with spades
Procedure and Calculations
Fig. 2. Circuit set-up used for the study of Ohm's Law by voltmeter-ammeter method.
Switch
V A 400mA
Power supply
Voltmeter
Ammeter
Resistor
V
A R
+ -
+ -
A DC mA
V DC V
OHM’S LAW AND RESISTANCE
PHY 161 LAB WORK 2 | 5
Fig. 5. Sample data of R vs I for tubular resistor, tungsten bulb and carbon bulb.
Questions
LAB WORK 3
LAB WORK 3 | 2 PHY 161
In order to better understand the relationship between the parameters in Eq. 2, see the interactive applet: http://phet.colorado.edu/sims/resistance-in-a-wire/resistance-in-a-wire_en.html
The resistivity of a conductor can be found by measuring its resistance and its dimensions. If a piece of wire of length L and diameter d is used as the conductor (Fig. 1), its resistivity can be calculated using formula (Eq. 3):
𝜌𝜌 =
Apparatus
Procedure and Calculations
Part I:
Fig. 2a – Circuit Set-up
Ro
Power Supply
R
0 cm 65 cm
- +
+ -
V A
A DC mA 400mA Vo
+
+
- - Switch Multimeter to measure voltage
Multimeter to measure current
V DC mV
RESISTIVITY
PHY 161 LAB WORK 3 | 3
Fig. 2b. Instruments and components posing for the circuit set-up photo.
Fig. 3. Sample reading of I and V as a function of length