Name _____ KEY ____________________________________ Date _________ Period ______
Inverse Square Law
I1 d12 = I2 d22
1.
Compare the intensity of light 2 m away from a lit match to the intensity 6 m away from
the match.

2.
How does the strength of a sound field 1 m from its source compare with its strength 4 m
away?

3.
I2
I2
d1
2
; I2 =
(I1)(d12)
d2
2
W
=
(1m2)(4 m)2
(8 m)
2
= 0.25 W/m2
=
d22
d12
; I2 =
(I1)(d12)
d22
=
(500 N)(6378 km)2
(19,134 km)2
= 55.6 N
Venus has a gravitational force of 8.87 N/kg. Its radius is 6,051 km. How far away from
the center of Venus would you need to move in order to experience a gravitational force
of 0.556 N/kg?
I1
I2
7.
=
d22
Earth’s radius is 6,378 km. If you weigh 500. N on Earth’s surface, what would you
weigh at a distance of 19,134 km from Earth?
I1
6.
At 3 m, the sound intensity will be 1/9th the intensity at 1 m away from the
parrot.
You stand 4 m away from a light and measure the intensity to be 1 W/m2. What will be
the intensity if you move to a position 8 m away from the bulb?
I1
5.
The field that is 1 m from the source has 16 times the intensity as the field 4
m from the source.
You are standing 1 m from a squawking parrot. If you move to a distance 3 m away, the
sound intensity will be what fraction of its original value?

4.
The light at 2 m will have 9 times the intensity as at 6 m from the match.
=
d22
(I1)(d12)
d1
I2
2 ; d2 = √
=√
(8.87 N/kg)(6051 km)2
(0.556 N/kg)
= 24200 km
Mercury has a gravitational force of 3.70 N/kg. Its radius is 2,439 km. How far away
from the center of Mercury would you need to move in order to experience a
gravitational force of 0.925 N/kg?
I1
I2
=
d22
(I1)(d12)
d1
I2
2 ; d2 = √
=√
(3.70 N/kg)(2439 km)2
(0.925 N/kg)
= 4878 km