Worksheet
Illuminance 1
Printer Friendly Version
The data shown to the right was procured using a light probe and a flickering candle in a completely darkened room. The x-axis has no relevance except to indicate that the data was collected within 60 seconds. The y-axis represents the number of lumens/m
^{2}
, or lux, that illuminated the probe's surface area.
The "plateaus" represent unique distances, or stations, at which the probe was positioned during the procurement of data. The distances are given in the data table shown below.
You first task is to determine an "average" value for the number of lux at each station. You will probably need to print the graph and then interpolate the heights of each plateau since they do not "exactly line up" with the grid lines provided.
Then you will graphically analyze the relationship between the magnitudes of the illumination and the distance from the light source. You may use a graphing program, such as EXCEL, or you can graph your data by hand on
graph paper
.
distance
illuminance
(m)
(lux)
0.15 m
0.25 m
0.35 m
0.45 m
0.55 m
0.65 m
Refer to the following information for the next question.
Your first graph will be
Illuminance vs Distance
.
Which graph shape shown below most closely matches your graph of
Illuminance vs Distance
?
Refer to the following information for the next question.
Now you will graph
Illuminance vs 1/Distance^2
.
Which graph shape shown below most closely matches your graph of
Illuminance vs 1/Distance
^{2}
?
Background Information
When a light source emits light, the light "expands" as an ever-growing light sphere. The illuminance represents the number of luminous flux (light rays) that fall on each square meter of the sphere's surface area.
Since the number of lumens emitted by the source is independent of the light sphere's growing size, we can write the following relationship:
This final formula tells us that the illuminance varies inversely as the square of the distance from the source. This is the same relationship as the force of gravity between two point masses and the electrostatic force between two point charges. The intensity of sound (in watts/m
^{2}
) also obeys this relationship.
Summary Questions
Calculate the surface area of a sphere having a radius of 0.20 meters.
Using the equation from your graph of
Illuminance vs 1/Distance
^{2}
, calculate the illumination, or lux, impinging on a square meter of this sphere's surface.
Using the information from the previous two questions, calculate the number of lumens released by the candle's flame.
Discuss the disadvantages of using a "candle" as a light source. Can you see when it was "flickering" in the data?
Related Documents
Lab:
Labs -
Directions: Constructive and Destructive Interference
Labs -
Doppler Effect: Source Moving
Labs -
Frequency of Vibrating Strings
Labs -
Hydrogen Spectrum
Labs -
Hydrogen Spectrum
Labs -
Illuminance by a Light Source
Labs -
Inertial Mass
Labs -
Interference Shading
Labs -
Pipe Music
Labs -
Reflection Gratings: Wavelength of a Helium-Neon Laser
Labs -
Relationship Between Tension in a String and Wave Speed
Labs -
Relationship Between Tension in a String and Wave Speed Along the String
Labs -
Ripple Tank Checklists
Labs -
Ripple Tank Checklists
Labs -
Ripple Tank Sample Solutions
Labs -
Ripple Tank Student Involvement Sheet
Labs -
Simple Pendulums: Class Data
Labs -
Simple Pendulums: LabPro Data
Labs -
Speed of a Wave Along a Spring
Labs -
Speed of Sound in Air
Labs -
Speed of Sound in Copper
Labs -
Using Young's Equation - Wavelength of a Helium-Neon Laser
Labs -
Video: Law of Reflection
Labs -
Video: Law of Reflection Sample Diagram
Resource Lesson:
RL -
Barrier Waves, Bow Waves, and Shock Waves
RL -
Beats: An Example of Interference
RL -
Incandescent Solids and Radiation
RL -
Interference of Waves
RL -
Interference: In-phase Sound Sources
RL -
Introduction to Sound
RL -
Law of Reflection
RL -
Physical Optics - Interference and Diffraction Patterns
RL -
Physical Optics - Thin Film Interference
RL -
Resonance in Pipes
RL -
Resonance in Strings
RL -
Ripple Tank Video Guides
RL -
SHM Equations
RL -
Simple Harmonic Motion
RL -
Sound Level Intensity
RL -
Speed of Waves Along a String
RL -
The Doppler Effect
RL -
Vibrating Systems - Simple Pendulums
RL -
Vibration Graphs
RL -
Wave Fundamentals
RL -
Waveform vs Vibration Graphs
REV -
Orbitals
Review:
REV -
Chapter 26: Sound
REV -
Honors Review: Waves and Introductory Skills
REV -
Physics I Review: Waves and Introductory Skills
REV -
Sound
REV -
Waves and Sound
REV -
Waves and Sound
Worksheet:
APP -
Echo Chamber
APP -
Santa's Helper
APP -
The Dog-Eared Page
APP -
The Low-Calorie Beer
APP -
The Perfect Pew
CP -
Colors
CP -
Interference
CP -
Light Properties
CP -
Polarization
CP -
Reflection
CP -
Shock Waves
CP -
Sound
CP -
Waves and Vibrations
NT -
Apparent Depth
NT -
Atmospheric Refraction
NT -
Concert
NT -
Electromagnetic Radiation
NT -
Light vs Sound Waves
NT -
Photographing Rainbows
NT -
Polaroid Filters
NT -
Shadows #1
NT -
shadows #2
NT -
Shock Cone
NT -
Soap Film Interference
NT -
Sound Waves
NT -
Standing Waves
NT -
Sunglasses
WS -
Beats
WS -
Beats, Doppler, Resonance Pipes, and Sound Intensity
WS -
Counting Vibrations and Calculating Frequency/Period
WS -
Doppler - A Challenge Problem
WS -
Doppler Effect
WS -
Double Slits
WS -
Fixed and Free-end Reflections
WS -
Fundamental Wave Terms
WS -
Illuminance 2
WS -
Interference: In-phase Sound Sources
WS -
Lab Discussion: Inertial and Gravitational Mass
WS -
More Practice with Resonance in Pipes
WS -
More Practice with the Doppler Practice
WS -
Practice with Resonance in Pipes
WS -
Practice with the Doppler Effect
WS -
Practice: Speed of a Wave Along a String
WS -
Pulse Superposition: Interference
WS -
Ripple Tank Review
WS -
Sound Vocabulary
WS -
Speed of Sound
WS -
Speed of Sound (Honors)
WS -
Standing Wave Patterns #1
WS -
Standing Wave Patterns #2
WS -
Standing Wave Patterns #3
WS -
Standing Wave Patterns #4
WS -
Thin Film Interference
WS -
Vibrating Systems - Period and Frequency
WS -
Wave Phenomena Reading Guide
WS -
Wave Pulses
WS -
Waveform and Vibration Graphs #1
WS -
Waveform and Vibration Graphs #2
TB -
25A: Introduction to Waves and Vibrations
TB -
25B: Vibrations and Waves
TB -
25C: Wave Speed
TB -
25D: Interference
TB -
25E: Doppler
TB -
25F: Doppler Effect (continued)
TB -
26B: Speed of Sound
TB -
26C: Resonance
TB -
26D: Beats
TB -
26E: Decibels
TB -
27A: Light Properties
TB -
27B: Properties of Light and Refraction
TB -
Decibels and Sound Intensity #1
TB -
Decibels and Sound Intensity #2
TB -
Interference Re-examined
TB -
Refraction Phenomena Reading Questions
TB -
Sound: Mixed Practice
TB -
Waves and Vibrations
PhysicsLAB
Copyright © 1997-2022
Catharine H. Colwell
All rights reserved.
Application Programmer
Mark Acton