National Aeronautics and Space Administration
Goddard Space Flight Center
Imagine the Universe!
Home
Science
Astronomer's Toolbox
Cosmic Objects
Big Questions
How Scientists Get Data
Featured Science
Special Exhibits
Satellites
Scientist Profiles
You Be the Astrophysicist
The Cosmic Distance Scale
Educators' Corner
Lesson Plans
Materials
Programs
Ask an Astrophysicist
Resources
Other Resources
Dictionary
Feedback
You Be the Astrophysicist
1 over R^2 quiz answers
Search
Inverse Squared Law Quiz
A light bulb looks dimmer the further away it is because
Most people are near sighted.
More light is absorbed by gas in between the bulb and the observer.
The same number of
photons
from the light bulb are spread out over a larger area.
Of the
Doppler
shift effect.
Light gets fainter with age.
Walking into your basement one night, you notice you can see only 10 feet with your trusty 50 Watt flashlight. How strong must your flashlight be in order to see the full 20 feet of your basement?
25 Watts
50 Watts
100 Watts
200 Watts
20 feet is too far to see with any flashlight!
While waiting for your bus you see in the distance the familiar glare of its headlights. With your handy
light
meter
you measure the intensity of its light as 10 lumen. After 10
seconds
you measure the intensity at 20 lumen. What can you infer about the bus during that 10 second interval?
The bus moved half the distance to you in those 10 seconds.
The bus was accelerating during those 10 seconds.
The bus was decelerating during those 10 seconds.
The bus moved less than half the distance to you in those 10 seconds.
The bus moved more than half the distance to you in those 10 seconds.