A Level Physics Practice Exam

If the slits' separation is increased while keeping the slit width constant, what will happen to the fringe pattern?

1. The fringe separation increases

2. The fringe separation decreases

3. The fringe pattern will disappear

4. The fringe pattern will become blurred

The correct answer is: The fringe separation increases

When the separation between the slits in a double-slit experiment is increased, while keeping the width of each slit constant, the fringe separation actually increases. This occurs due to the relationship between slit separation, wavelength, and fringe spacing in the interference pattern formed on a screen. The formula for the fringe separation (the distance between successive bright or dark fringes) in a double-slit interference pattern is given by: \[ x = \frac{\lambda L}{d} \] where \( x \) is the fringe separation, \( \lambda \) is the wavelength of the light used, \( L \) is the distance from the slits to the screen, and \( d \) is the separation between the slits. As the separation \( d \) is increased, keeping the wavelength \( \lambda \) and the distance \( L \) constant, the value of \( x \) increases. This means that the fringes move further apart from each other, resulting in a larger spacing between the bright and dark fringes on the screen. This behavior is crucial in understanding wave phenomena and interference, illustrating how manipulating physical parameters can alter observable patterns. The options relating to blurring or disappearance of the fringe pattern would only arise under different