How Light Spreads OutLesson 4

What’s the deal?The Sun is one

medium size star.The Andromeda

Galaxy is a cluster of hundreds of billions of stars*, most are larger than the Sun.

Why is the Sun so incredibly much brighter than the whole Andromeda Galaxy?

*710,000,000,000 solar masses according to Wikipedia.

What should I put in my data table?

Ideal Data (Don’t Change Yours)

Distance from Light

Source

Area of Illumination

(Lit Area)10 cm 1 cm2

20 cm 4 cm2

30 cm 9 cm2

40 cm 16 cm2

50 cm 25 cm2

What kind of graph should we use?

Extrapolating: Estimating beyond the measured/recorded data.

10 30 50 70 900

20

40

60

80

100

120

Distance from Light vs. Area of Il-lumination

Distance from Light (cm) vs. Area of Il-lumniation (cm2)

Are

a o

f Il

lum

inati

on

(cm

2)

Distance from Light Source (cm)

Exponential Relationship

10 20 30 40 50 60 70 800

10

20

30

40

50

60

70

Distance from Light Source vs. Area of Illumination

Area of Illumination

Distance from the Light Source

Are

a o

f Il

lum

inat

ion

Formula:Area of Illumination = (Distance to Light

Source/10)2

y=(x/10)2 Where y=Area of Illumination and x=Distance to the Light Source

Big idea: As light leaves the source the light spreads

out and becomes weaker (less energy) exponentially.