Why does Malus law give I₀ at 0° but textbook shows I₀/2?

[Suyash Singh]

Homework Statement

It is just a conceptual doubt

Homework Equations

According to malus law intensity of light through polaroid is
I=(Io)cos^2(theta) where theta is the angle between axis of polaroid and incident light.

The Attempt at a Solution

But when Theta=0 then I=Io but in my book it is I=Io/2.
why??

and also is my diagram below correct?

--->(light)(I) [](polaroid) --->(I/2) [] --->(I/4) (theta=0 degrees for both polaroid)

 

[gneill]

$I_o$ is generally taken to be the intensity of the light after an unpolarized source has passed through one polarizer (hence polarizing it). Half of intensity of the source is lost by the first polarization.

Take a look at the diagram for the Law of Malus entry on the Hyperphysics web site:

http://hyperphysics.phy-astr.gsu.edu/hbase/phyopt/polcross.html#c1

 

[Suyash Singh]

Thankyou :)