A source of light is placed in front of a screen. Intensity of light on the screen is \( I \). Two Polaroids \( P_1 \) and \( P_2 \) are so placed in between the source of light and screen that the intensity of light on screen is \( \dfrac{I}{2} \). \( P_2 \) should be rotated by an angle of __________ (degrees) so that the intensity of light on the screen becomes \( \dfrac{3I}{8} \).
