UNIVERSITY OF MISSOURI - COLUMBIA
DEPARTMENT OF MECHANICAL AND AEROSPACE ENGINEERING
MAE 3800 Instrumentation and Measurements Laboratory
Z.C. Feng
Copyrighted, January 2013
EXPERIMENT #1 Resistance, Voltage, and Current measurement: Estimation of temperature of the tungsten filament
inside an incandescent light bulb
Due: 5:00pm, Tuesday, Feb. 5
1 Introduction:
We are aware that a light bulb can get very hot when turned on. The heat generated by a light bulb is considered a
form of wasted energy if illumination from the light bulbs is the only desired output. It is thus not surprising that new
and more efficient light sources do not generate much heat. In this experiment, we will conduct measurements of an
incandescent light bulb to answer the question “How hot does a light bulb get?”
1.1 Objectives
To use multimeters (DMM) for resistance, voltage, and current measurements
To obtain tungsten filament temperatures of a light bulb when operated at different power
1.2 Equipment:
Fluke digital multimeters (DMM)
A DC Power Supply
An incandescent light bulb
1.3 Report format
For this experiment you do not have to write a report. Use the answer sheet to record and analyze data.
2. Description of Equipment
Digital multimeters (DMM) are versatile instruments that combine the measurements of several electrical quantities in
a single unit. Although the meters are intuitively designed and their usage is easy to understand, care must be taken
since what appears to be a single meter actually has several meters with many functions packed in it.It is very
important to realize that the circuit connection for current measurement is different from that for resistance
measurement or voltage measurement.
3. Procedures and circuit connection
3.1 Resistance measurement
Measure and record the resistance of the light bulb. The bulb should not be connected to any other components when
taking the resistance measurement. This resistance is the resistance of the tungsten filament at room temperature. We
may denote it by R300K.
Figure 1. Electrical connection for simultaneous voltage and current measurement using two DMMs.
3.2 Voltage and Current measurement
Connect the circuit as shown in Figure 1. A DC Power Supply functions light a battery. However, its output
voltage/current can be controlled to a desired value.
3.3 Set the DC Power Supply output voltage to 1 volt. Record the voltage and the current read by the meters. Note that
meters can measure AC as well as DC. A option button may need to be pushed to switch between the two. Repeat the
process by setting the output voltage to, roughly, 2, 3, 4, 5, 6, and 7 volts. The errors in output setting will not affect
accuracy of our measurement. However, you may need to wait until the output settles to a steady-state following the
setting adjustment.
3.4 Use the measurement data calculate the resistance of the light bulb when different voltages are applied.
3.5 Divide the resistances by the resistance at room temperature, i.e. R300K.
3.6 Use the Table 1 to obtain the temperature based on the R/R300K.. You may need to do linear interpolation for values
of R/R300K that are not given in the table. (Table taken from Resistivity of Tungsten,
hypertextbook.com/facts/2004/DeannaStewart.shtml. Data given in CRC Handbook of Chemistry and Physics are
limited to below 900K)
4. Observe a demonstration of current measurement by measuring voltage over a concatenated small resistor.
Suppose you want to measure the current drawn by a home appliance:
Electric
Appliance
110V AC
current=?
The current can be calculated from voltage measured over a small resistor as shown in Figure 2 below.
Electric
Appliance
mA
V, 
Small
Resistor
110V AC
Isolating (Safety)
Transformer
COM
DMM for AC voltage
measurement
Figure 2. Schematic diagram of current measurement using a concatenated small resistor. The isolating transformer
provides protection against accidental contact with the exposed connector. A light bulb is used to represent an Electric
Appliance. Current through the light bulb is obtained by measuring the voltage over the Small Resistor.
Observe this demonstration, Answer the questions in the report answer sheet.
Report for Lab 1
Student name:.
Group #:
.
Do not directly record the data on these sheets. Record them in your lab notebook. Copy over the data once you are
certain they are correct. Points will be deducted for messy and illegible lab reports.
1 (1 point) Resistance measurement
Record the resistance measured by the DMM when the bulb is not connected to any source and the bulb is at room
temperature (27oC=300K).
R300K =
2. (5 points) Record voltage and current measurement. Calculate the next three columns. Calculate the last column
using Table 1 given.
DC Volt
(Approx)
1.
V
I
R=V/I
R/ R300K
P=V I
Temp
2.
3.
4.
5.
6.
7.
3. (2 point) Answer True or False to the following questions:
(a) The resistance of the bulb is independent of the filament temperature.
(b) The resistance of the bulb increases with the power.
(c) Part of the energy consumed by a light bulb is wasted in the form of heat.
(d) The hotter the filament, the more energy efficient the light bulb is.
4. Answer the following questions related to the lab demonstration on current measurement using a concatenated
small resistor
4.1 (1 points) An incandescent light bulb can be regarded as a resistor. If its power output is 100W, calculate the
resistance of the light bulb and the current drawn by the light bulb, assuming the voltage of the power source is 110V.
4.2 (1 point) The actual current drawn by the light bulb can be obtained by measuring the voltage over a small resistor
which is inserted into the circuit as shown in Figure 2. The insertion of this small resistor obviously affects the current.
However, if the resistance is small when compared with the resistance of the light bulb, the error is negligible. If the
small resistor is 1  , calculate the voltage over the small resistor for the case given in 4.1.
5. (5 points) Compact florescent light (CFL) uses a fraction of the power consumed by an incandescent bulb (IB) for
the same amount of light output measured in lumens. Design an instrument setup that demonstrates to the general
public in an intuitive way this significant energy savings. Although you are urged to be creative in your design and
there is no standard answer, you may assume that two DMMs are available to you together with CFLs and IBs (with
the same output lumens). Note that CFLs and IBs available from stores require 110V AC. State the electrical quantity
(or quantities) you plan to measure and draw diagrams to show circuit connection.