A Level Physics Practice Exam

In a double slit experiment, what factor increases the fringe separation?

1. Increasing the slit width

2. Decreasing the wavelength of light used

3. Decreasing the distance to the screen

4. Increasing the distance between the slits

The correct answer is: Increasing the distance between the slits

In a double slit experiment, the fringe separation is defined by the interference pattern created when coherent light waves pass through two closely spaced slits and overlap on a screen. The formula for fringe separation (also known as fringe width) is given by: \[ \Delta y = \frac{\lambda L}{d} \] where: - \( \Delta y \) is the fringe separation, - \( \lambda \) is the wavelength of the light, - \( L \) is the distance from the slits to the screen, - \( d \) is the distance between the slits. Increasing the distance between the slits \( d \) leads to a decrease in \( \Delta y \). In contrast, when the distance \( d \) is increased, it means that the interference pattern becomes more compact, leading to a smaller angle of separation for the fringes on the screen. The correct answer indicates that increasing the distance between the slits is the factor that directly influences the fringe separation. The fringe width is inversely proportional to the slit separation, meaning that a larger distance between the slits results in closer spaced fringes. In contrast, increasing the slit width does not change the separation of the fringes; rather, it