Question

In Young's double-slit experiment, both slits were illuminated by a laser beam and the interference pattern was observed on a screen. If the viewing screen is moved farther from the slits, what happens to the interference pattern? a) The pattern gets brighter. b) The pattern gets brighter, and the maxima are closer together. c) The pattern gets less bright, and the maxima are farther apart. d) There is no change in the pattern. e) The pattern becomes unfocused. f) The pattern disappears.

Short answer

Answer: The pattern gets less bright, and the maxima are farther apart.

Step-by-step solution

Recall the formula for fringe spacing

In Young's double-slit experiment, the formula for fringe spacing (distance between consecutive maxima) is given by: d = \frac{L \lambda}{a}, where d is the fringe spacing, L is the distance between the slits and the screen, λ is the wavelength of the light, and a is the slit separation.

Analyze the effect of moving the screen farther from the slits on fringe spacing

According to the formula in step 1, fringe spacing (d) is directly proportional to the distance (L) between the screen and the slits. Thus, as the screen moves farther away from the slits (L increases), the fringe spacing will also increase. Consequently, the maxima will be farther apart from each other.

Analyze the effect of increasing distance on the pattern brightness

The brightness of the interference pattern is determined by the intensity of light reaching the screen. As we move the screen farther from the slits, the intensity of light (energy per unit area) decreases, as light spreads out over a larger area. As a result, the pattern will become less bright.

Choose the correct option

With the conclusions from steps 2 and 3, it is clear that the interference pattern becomes less bright and the maxima are farther apart when the screen is moved farther from the slits. This corresponds to option c, so the answer is: c) The pattern gets less bright, and the maxima are farther apart.