When a tiny circular obstacle is placed in the path of light from a distant source, a bright spot is seen at the centre of the shadow of the obstacle. Explain why?

In Fraunhofers' diffraction, the source of light and screen are kept at __________ distance from the obstacle.

Consider a light beam incident from air to a glass slab at Brewster's angle as shown in figure . A polaroid is placed in the path of the emergent ray at point P and rotated about an axis passing through the centre and perpendicular to the plane of the polaroid .

Select the correct option from the given alternatives.A horse is ties to a post by a rope.If the horse moves along a circular path,always keeping the rope tight and describes 88 metres when it traces the angle of 72^@ at the centre,then the length of the rope is

A point source is placed at co-ordinates (0, 1) in X-Y plane. A ray of light from the source is reflected on a plane along the X-axis and peipendicular to the X-Y plane. The reflected ray passes through the point (3,3). What is the path length of the ray from (0, 1) to (3, 3)?

In Young's double slit experiment the slits are 0.5 mm apart and interference is observed on a screen placed at a distance of 100 cm from the slits. It is found that the 9th bright fringe is at a distance 8.835 mm from the second dark fringe from the centre of the fringe pattern. Find the wavelength of light used.

Figure given below shows a beam of light converging at point P. When a concave lens of focal length 16 cm is introduced in the path of the beam at a place O shown by dotted line such that OP becomes the axis of the lens, the beam converges at a distance x from the lens. The value x will be equal to

In a biprism experiment, the fringes are observed in the focal plane of the eye piece at a distance of 1.2m from the slits. The distance between the central bright band and 20th bright band is 0.4 cm. When a convex lens is placed between biprism and the eyepiece, the distance between the two vertical magnified images is found to be 0.9 cm. Determine the wavelength of light used.

When a monochromatic point source of light is at a distance of 0.2 m from a photoelectric cell, the cut-offf voltage and the saturation current are respectively 0.4 V and 12 mA. If the same source is placed 0.4 m away from the photoelectric cell, then