Plane electromagnetic waves of wavelength 589 nm (yellow light) from a sodium la
ID: 1454962 • Letter: P
Question
Plane electromagnetic waves of wavelength 589 nm (yellow light) from a sodium lamp are incident horizontally from the left on an opaque vertical screen having a single slit - shaped opening of height D = 1.25 x 10^-6 m, and are diffracted. Light emerging from the slit forms an at the center of the vertical screen 25.0 cm to the right. Maximum brightness is observed at the center of the pattern, corresponding to an undeflected light beam. At what angle theta below the horizontal is the first dark fringe or minimum in brightness, i. e. what is the angular half - width of the central bright spot 0.471 deg 28.1 deg 30.4 deg 0.506 deg 34.9 degExplanation / Answer
b)28.1 degrees
we know,
for first diark fringe,
D*sin(theta) = lamda
sin(theta) = lamda/D
theta = sin^-1(lamda/D)
= sin^-1(589*10^-9/(1.25*10^-6))
= 28.1 degrees