We can find the angle at which a first minimum is obtained in the diffracted light by the following reasoning. The light from a source located at the top edge of the slit interferes destructively with a source located at the middle of the slit, when the path difference between them is equal to λ λ / 2 . Similarly, the source just below the top of the slit will interfere destructively with the source located just below the middle of the slit at the same angle. We can continue this reasoning along the entire height of the slit to conclude that the condition for destructive interference for the entire slit is the same as the condition for destructive interference between two narrow slits a distance apart that is half the width of the slit. The path difference is approximately d sin ⁡ ⁡ ( θ θ ) 2 so that the minimum intensity occurs at an angle θ θ min given by d sin ⁡ ⁡ θ θ min = λ λ , where d is the width of the slit, θ θ min is the angle of incidence at which the minimum intensity occurs, and λ λ is the wavelength of the light.