GRADE 9 SCIENCE
Watts the Difference?
Investigating Light Bulb Efficiency
Curriculum Expectations
SNC 1D Physics: The Characteristics of Electricity
Understanding the Concepts
PH1.06
State the SI units of potential difference, electric current, electrical
resistance, electrical energy, and power (e.g., volt, ampere, ohm, joule,
watt and kilowatt).
PH1.11
Determine quantitatively the percent efficiency of an electrical device
that converts electrical energy to other forms of energy, using the
relationship
[ percent efficiency = ( energy output / energy input ) x 100 ]
Developing Skills of Inquiry and Communication
PH2.01
Through investigations and applications of basic concepts, demonstrate
knowledge of electrical safety procedures when planning and carrying
out an inquiry, and choosing and using materials, tools and equipment.
PH2.03
Through investigations and applications of basic concepts, demonstrate
the skills required to plan and conduct an inquiry into electricity using
instruments, tools and apparatus safely, accurately and effectively (e.g.,
use an ammeter and a voltmeter to measure current and potential
difference in a circuit).
PH2.05
Through investigations and applications of basic concepts, gather and
record qualitative and quantitative data using an appropriate format,
and analyse the data to explain how the evidence gathered supports or
refutes an initial hypothesis (e.g., explain the variations in the monthly
costs of electrical energy).
PH2.06
Through investigations and applications of basic concepts, communicate
ideas, procedures, results and conclusions using appropriate SI units,
language and formats, and evaluate the processes used in planning,
problem solving, decision making, and completing the task.
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SNC 1P Physics: Electrical Applications
Overall Expectations
PHV.03
Analyse the practical uses of electricity and its impact on everyday life.
Understanding Basic Concepts
PH1.07
Determine quantitatively the percent efficiency of an electrical device
that converts electrical energy to other forms of energy, using the
relationship
[ percent efficiency = (energy output / energy input) x 100 ]
Developing Skills of Inquiry and Communication
PH2.01
Through investigation and the applications of basic concepts,
demonstrate knowledge of electrical safety procedures when planning
and carrying out investigations and choosing and using materials, tools
and equipment.
PH2.02
Through investigation and the applications of basic concepts, identify an
authentic practical challenge or problem related to the use of electricity
(e.g., to design household wiring; to increase the efficiency of electrical
usage in the school).
PH2.04
Through investigation and the applications of basic concepts,
demonstrate the skills required to plan and conduct an inquiry into the
use of electricity using instruments, tools and apparatus safely,
accurately and effectively.
PH2.06
Through investigation and the applications of basic concepts, organize,
record and analyse the information gathered (e.g., interpret patterns
and trends; discuss relationships among variables; and predict
consequences of action or inaction).
PH2.07
Through investigation and the applications of basic concepts,
communicate scientific ideas, procedures, results and conclusions using
appropriate SI units, language and formats (e.g., electrical power,
voltage, resistance; drawings, charts, graphs).
Relating Science to Technology, Society and the Environment
PH3.02
Develop a solution to a practical problem related to the use of electricity
in the home, school or community (e.g., choose an appropriate fuse or
circuit breaker for a specific circuit).
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Introduction
The burning of fossil fuels causes much pollution. To help reduce this problem each of us
must conserve energy. One way is to use fewer things that use energy and to use them for
less time. Another way is to keep using things, but make certain they are energy efficient.
The amount of energy that can be saved by being smart about the light bulbs you use may
surprise you! The efficiency of a light bulb depends on how much useful light is given off.
Useful light is call illumination, and is measured in lumens. The power going into the
bulb is measured in watts. You can find the efficiency by dividing lumens by watts. Is a
100 watt light bulb more efficient than two 50 watt bulbs? Are all same-watt light bulbs
equally efficient? In this activity you will test different light bulbs to see which one is the
best to use.
Purpose
How can the efficiency of light bulbs be determined?
Hypothesis
Predict which light bulb will be the most efficient.
METHOD A: TEMPERATURE PROBE / LIGHT SENSOR
Materials
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LabPro interface
Data Pro program
Temperature probe
ring stand
tape
Assorted light bulbs (incandescent, compact fluorescent)
Palm handheld
Light sensor
4 cm piece of drinking straw
2 utility clamps
ruler
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Procedure
Figure #1: Setting up the light sensor
Figure #2
1. Prepare the sensors for data collection.
a) Tape the straw to the table surface as shown in Figure 1.
b) Insert a Temperature Probe into the straw as far as it will go. Check to make sure
the end of the Temperature Probe is not touching the tabletop.
c) Place the piece of white paper over the Temperature Probe.
d) Use a utility clamp and ring stand to fasten a Light Sensor 5 cm above a piece of
coloured paper as shown in Figure 2. The Light Sensor should be set on the 0-6000
lux position if it has a switch.
e) Use the other utility clamp to fasten the lamp and bulb to the ring stand 10 cm
above the paper.
f) The classroom lights should be on.
2. Plug the Light Sensor into Channel 1 and the Temperature Probe into Channel 2 of the
LabPro interface. Connect the handheld to the LabPro using the interface cable. Firmly
press in the cable ends. Firmly press in the cable ends.
3. Press the power button on the handheld to turn it on. To start Data Pro, tap the Data
to
Pro icon on the Applications screen. Choose New from the Data Pro menu or tap
reset the program.
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4. Set up the handheld and interface for a Light Sensor in CH 1 and a Temperature Probe
in CH 2.
a) On the Main screen, Tap
.
b) If the handheld displays LIGHT or LIGHT(lx) in CH1 and TEMP(C) in CH2,
proceed directly to Step 5. If it does not, continue with this step to set up your
sensors manually.
c) On the Setup screen, tap
.
d) Press the Scroll buttons on the handheld to scroll through the list of sensors.
e) Choose LIGHT 6000(lx) from list of sensors.
f) Tap
.
g) Press the Scroll buttons on the handheld to scroll through the list of sensors.
h) Choose the correct Temperature Probe (in oC) from list of sensors.
5. Set up the handheld and interface for data collection.
a) While still on the Setup screen, tap
.
b) Enter “10” as the time between samples in seconds, using the on-screen keyboard
(tap “123”) or using the Graffiti writing area.
c) Enter “60” as the number of samples. (Data collection will last 10 minutes.)
d) Tap
twice to return to the Main screen.
6. Switch on the light bulb. Tap
to begin data collection.
7. When data collection is complete, determine and record the mean light reflection value
and the minimum and maximum temperature readings.
a) After data collection stops, tap
.
. Statistics for the light reflection data will be in
b) On the Analyze screen, tap
the first row and the temperature data will be in the second row.
c) Record the Mean light reflection value in your Data table (to the nearest whole lux).
The lux is the SI unit for light illumination.
d) Record the Min (minimum) and Max (maximum) temperature readings (round to
the nearest 0.1oC).
twice to return to the Graph screen.
e) Tap
8. Repeat Steps 6 - 7 for Compact Fluorescent Light bulb. If time allows, make and record
readings for two additional colours of paper.
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Observations
Incandescent
Compact Fluorescent
Additional
Light Bulb
Light Bulb
Light Bulb
Starting Temperature
(Co)
Final Temperature (Co)
Change in
Temperature (Co)
Light Intensity (lux)
Method B: Low Budget Photometer
Materials
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2 blocks (wood or paraffin) about 10 x 15 x .5 cm
2 different light bulbs (incandescent vs compact fluorescent)
and sockets
metre stick
aluminum foil
scissors
clear tape
other light bulbs (optional)
Procedure
Teacher’s Note: To view the apparatus and its operation, visit the following website:
http://groups.physics.umn.edu/demo/optics/6B1030.html
1. Cut two pieces of aluminum foil so that they are the same size as the blocks. Place the
dull sides of the aluminum foil back to back. Place a block of paraffin wax on each
shiny side. Seal your photometer (light metre) with clear tape along the sides where
the blocks meet. Refer to Figure #1.
Figure #1
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2. Place the metre stick flat down between two 100 watt light bulbs and sockets. Stand
the paraffin about 10 cm from one bulb. Review electric safety procedures with your
teacher. Turn on the bulbs and note that one side of the metre is much brighter than
the other.
3. Move the photometer until the light appears to be equally bright on both sides. Record
the wattage of the bulbs, their distance to the photometer, and the lumen ratings as
stated on their packages.
4. Leave one 100 watt bulb as standard. Use a 50 watt or 25 watt bulb in the other
socket. Repeat procedure 3.
5. Repeat procedure 3 using a compact fluorescent and a regular bulb with the same
lumen rating.
6. Repeat procedure 3 using two bulbs with equal watt rating but different lumen ratings.
7. Repeat procedure 3 with any additional bulbs, as directed with your teacher.
8. Calculate the relative efficiency of each bulb in terms of power output in lumens
divided by power input in watts.
Observations
INCANDESCENT LIGHT BULB
Watts
Lumens
Distance
to metre
(cm)
Effic.
Lumens/
Watt
COMPACT FLUORESCENT LIGHT BULB
Watts
Lumens
Distance
to metre
(cm)
Effic.
Lumens/
Watt
Analysis
1. In terms of energy efficiency, which bulb appears to be the best? Explain.
2. Provide a comparison of the amount of heat produced between the various types of
light bulbs tested. What does this indicate about the efficiency of the bulbs?
3. When oil is used to make electricity, it takes about one barrel of oil to supply 650
kilowatt hours of electrical energy. Obtain the wattage and the cost to buy each bulb.
a) Calculate the energy consumed by each bulb knowing that a consumer uses each
bulb for a year (365 days x 4 hours per day).
b) How much oil would each light bulb consume in a year?
c) Compare the cost of the bulb with the cost of energy consumed. Which type of bulb
is the best buy and how much would the consumer save in one year, 5 years and 10
years?
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Conclusions
Suggested Websites for Support
The “Live Brightly, Save Energy Too” brochure provided by Hydro One can be obtained at
the following website:
http://www.hydroonenetworks.com/en/efficiency/downloads/PowerSaver_02_Lig
hting.pdf
The “Switch and Save” brochure provided by Hydro One can be obtained at the following
website:
http://www.hydroonenetworks.com/en/efficiency/switch_and_save/default.asp
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Hydro One “Live Brightly, Save Energy Too” brochure
http://www.hydroonenetworks.com/en/efficiency/downloads/PowerSaver_02_Lighting.pdf
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WATTS THE DIFFERENCE?
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Hydro One “Switch and Save” brochure
http://www.hydroonenetworks.com/en/efficiency/switch_and_save/default.asp
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WATTS THE DIFFERENCE?
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