Introduction to Electronics - Faculty.chemeketa.edu

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Oct 7, 2013 (3 years and 6 months ago)

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Introduction to Electronics


Introduction

The purpose of this lab is to understand basic electronic measurements, components, and test
equipment. The majority of electronic instrumentation is based on the concepts of current, potential
diffe
rence, and resistance.


1)

Current (I) is the time rate of flow of charge through a device. The SI unit of current is the
ampere (amp or A).

2)

Potential difference (
ΔV, often abbreviated as V) is the electrical potential energy per unit
charge. The SI unit of potential difference is the volt (V).

3)

Resistance (R) is the ratio of potential difference to current. The SI unit of resistance is the
ohm (Ω).


Note on terminol
ogy: Distinguish between a quantity and its SI unit. Avoid referring to current as “amperage” and
potential difference as “voltage”.

Add these two terms to the list of banned expressions in lab reports.


Electrical components and test equipment can be conn
ected together in either series or parallel
configurations. Two components are “in series” if they are connected to each other end
-
to
-
end and no
other component is connected to that junction. Two components are “in parallel” if they are
connected at both e
nds.


In this lab, you will investigate some simple electronic circuits and components. At the end of this lab,
you should be able to read the color code on a resistor and use a digital multi
-
meter to measure
resistance, potential difference, and current.
You will also do a simple test of Ohm’s law.


Equipment You Procure



digital camera



9V battery


Equipment from Kits



2 digital multi
-
meters



9V battery connector



All resistors



Styrofoam chunk



clips


Experimental Procedures

1
) Using the color
-
code chart provid
ed

on the
last

page
,

compute and record the
theoretical resistance
and error
of each resistor.

Convert the percentage error to an absolute error.


2)
Us
e

a

digital multi
-
meter as an
ohmmeter
(see instructions on the
last

page)
to

measure and record
the

exp
erimental
resistance of each re
sistor.
Include an
explicit
estimation of the error

in the
experimental resistance (see instructions on the last page).
Compare the
theoretical and experimental
resistances
. Do the resistor
s

work as advertised?


3) Create a c
ircuit
as shown
using
an approximately

1000 ohm resistor,
clips
, 9V battery, 9V battery
connector
,

a digital multi
-
meter configured as a 20V voltmeter (see instructions on the last page), and a
digita
l multi
-
meter configured as a 2
0 mA ammeter (see instruc
tions on the last page).

Connect the
battery last.
Be very careful to use the ammeter correctly since it is very easy to blow a fuse.

You may
choose to take a photograph of your configuration without the battery connected and e
-
mail it to your
instructor t
o check.


4) Measure and record the
experimental
potential difference

and current
.

Include an estimation of the
error for both the
potential difference

and current.


5
) Divide the measured
potential difference

by the
previously
measured resistance to
obtai
n a
theoretical current
.
Propagate the error in the calculations according to the general lab instructions.
Compare to the value measured in step
4
.

Did Ohm’s law make a correct prediction?



Figure 1:
The digital multi
-
meter in the upper right corner is
configured as an ammeter at the 20 mA setting. It reads
9.31 ± 0.02 mA or 0.00931 ± 0.00002 A. The digital multi
-
meter in the lower right corner is configured as a voltmeter
at the 20 V setting. It reads 9.21 ± 0.02 V. Connect the battery last so that you
can reduce the risk of damaging your
ammeter.
Resistor Color Codes

Black

Brown

Red

Orange

Yellow

Green

Blue

Violet

Gray

White

0

1

2

3

4

5

6

7

8

9

First find the tolerance band. It will typically be red (2%), gold (5%), or silver (10%) and slightly separa
ted from the other
bands. Starting from the opposite end, identify the first band and write down the number associated with that color. Now
'read' the next color and write down the number associated with that color. Now read the third or 'multiplier' band
and
write down that number of zeros.

Digital Multi
-
Meter as an Ohmmeter

The digital multi
-
meter should come with 2 cables. Plug the red one into the hole labeled
“V/Ω”. Plug the black cable into the hole marked “COM”. Turn the dial to the region marked
“OHM” and the setting that is the lowest possible and still above your expe
cted resistance.
Place the red lead and the black lead at opposite ends of a resistor or group of resistors that is
not connected to anything else
. The reading displayed will be the resistance in units as
specified by the setting. If the setting is 200, th
en the resistance will be measured in Ω. If the
setting is 2K, 20K, or 200K, then the resistance will be measured in kΩ. If the setting is 2M or
20M, then the resistance will be measured in MΩ.

Digital Multi
-
Meter as a Voltmeter

Place the cables in the sa
me holes as with the ohmmeter. Turn the dial to the
region marked “DCV” for DC circuits or “ACV” for AC circuits. Choose a
setting that is the lowest possible and still above your expected potential
difference. Place the leads at opposite ends of a circuit

element or combination of
elements and observe the potential difference or potential difference across the
circuit element or combination of elements in units as specified by the setting. If
the setting is 200m, then the potential difference will be measu
red in mV. If the
setting is anything else, the potential difference will be measured in V.

Digital Multi
-
Meter as an Ammeter

Please be careful using the digital multi
-
meter as an ammeter because it is a sensitive
device. Plug the red cable into the hole
labeled “A”

or “mA”
. Plug the black cable into
the hole marked “COM”. Turn the dial to the region marked “DCA” for DC circuits or
“ACA”

for AC circuits. Place the ammeter “in series” with the circuit element you wish
to measure current through. To place the ammeter “in series” with the circuit element,
disconnect one connection to the circuit element, then connect one lead to the circuit
element and connect the other lead to the point where the circuit element used to be
connected. The ammeter should now measure the current in units as specified by the
setting. If the ammeter setting is 200μ, then the current will be measured in μA. If the

ammeter setting is 2m, 20m, or 200m, then the current will be measured in mA. If the
current setting is 2, then the current will be measured in A.

Note: Never connect an ammeter “in parallel” to a circuit element of interest because it might blow a fuse a
nd will
definitely not measure the current through the circuit element. Please consult with your instructor if this is not clear.

Error with the Digital Multi
-
Meter

You may a
ssume that the last digit displayed is ±2 unless
you have evidence otherwise. Thes
e error estimations must be
made specific to each measurement in your reports.

Save this page for future use!

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O

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