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In the Young's double slit experiment, a monochromatic light source is incident on two closely spaced narrow slits. The light waves pass through the slits and travel onward to a screen placed at some distance from the slits. As the light waves overlap, they create interference patterns on the screen.

When the waves have the same phase, they add together and cause constructive interference, leading to a bright fringe on the screen. Conversely, when the waves are out of phase, they cancel each other out and cause destructive interference, leading to a dark fringe on the screen. The pattern of alternating bright and dark fringes is called an interference pattern.

For a Young's double slit experiment, the path difference between the two light waves determines the interference pattern. When the path difference is an integer multiple of the wavelength, constructive interference occurs, and when the path difference is an odd integer multiple of half the wavelength, destructive interference occurs. The path difference between the two waves depends on the angle between the wavefronts and the screen. In the central position (where the angle is 0°), the path difference is 0, and we have a bright fringe. As we move away from the central position, the path difference increases, leading to alternating bright and dark fringes. The angle in which we observe the constructive interference is given by the formula: \[\sin{\theta} = \frac{m \lambda}{d}\] Where \(m\) is the order of the bright fringe, \(\lambda\) is the wavelength of the light, and \(d\) is the distance between the slits.

As we move away from the center on the screen, the points of constructive interference form a series of equally spaced fringes, which are straight lines. Therefore, in a Young's double slit experiment, the shape of the interference fringes formed on a screen is: (D) Straight line