Does bringing slits closer together increase or decrease intensity of interference pattern Does bringing the slits together affect the intensity of maxima for double slit experiment and also the diffraction grating? Does decreasing slit width affect the intensity of the maxima for a single slit experiment. 
 A: First, let me tell you that amplitude is proportional to slit width because as slit width increases, more light gets through, so more energy is transmitted, and therefore, the amplitude must also get bigger (by the same factor).
Furthermore, intensity is proportional to amplitude squared.
By applying the 2 above statements, we get that intensity is proportional to slit width squared.
For the picture below, the x and y only represent that there is some kind of part in the equation, it is just not shown here, instead, it is denoted as x and y.

Answering below to: Does decreasing slit width affect the intensity of the maxima for a single slit experiment?
So, if we for example, reduce the width of the slit by a factor of two (we halve the width), what is going to happen, is that intensity will decrease by a factor of four.
$I$ = the central intensity before the width of the slit is reduced.
$I_1$ = the central intensity after the width of the slit is reduced by 2.
And since intensity is proportional to slit width squared, we will have $$I_1 = z\left(\frac d2\right)^2 = z(\frac{d^2}{4})$$ So, $d^2$ is reduced by 4, and because $d^2$ is directly proportional to intensity, $I$ (intensity) is reduced by 4. (The z represents some part of the equation).
So, yes, reducing the width of a slit decreases the intensity of the central maxima in a single slit experiment.
I hope that this helped! :)
