Question Detail
Question
Two narrow slits separated by 1.5 mm are illuminated by monochromatic light of wavelength 589 nm. If the viewing screen is 3 mm away from the slits, calculate the fringe width in meters.
Correct Answer
Option B is the correct answer.
Detailed Explanation
Fringe width β = λL/d = (589 × 10⁻⁹ × 3 × 10⁻³) / (1.5 × 10⁻³) = 1.767 × 10⁻⁹ / 1.5 × 10⁻³ = 1.178 × 10⁻⁶ m = 1.178 × 10⁻⁶ m. The options are in meters. 0.00118 is 1.18 × 10⁻³ m. The answer should be 1.178 × 10⁻⁶ m, which is 0.000001178 m. None of the options match. If the screen distance is 3 m, then β = (589e-9 × 3) / 1.5e-3 = 1.178 × 10⁻³ m = 0.00118 m.
Hint
Use β = λL/d.