Answer
48.1 percent
Work Step by Step
Let the initial intensity be $I_o$.
Use equation 24–5. For the first polarizer, the angle between the light’s polarization axis and the polarizer’s axis is $21.0^{\circ}$.
After the light emerges it is polarized along that axis, and when it passes through the second polarizer, the angle between the light’s polarization axis and the second polarizer’s axis is $42.0^{\circ}$.
Use Eq. 24–5 twice.
$$I_1=I_ocos^2\theta=I_o cos^2 21.0^{\circ}$$
$$I_2=I_1cos^2\theta= I_o (cos^2 21.0^{\circ})(cos^2 42.0^{\circ})=0.481I_o$$