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### What is diffraction

• It is a common observation with the waves of all kinds that they bend round the edge of an obstacle.

• Light like other waves also bends round the corner but in comparison to sound waves small bending of light is due to very short wavelength of light which is of the order of 10-5 cm.

• This effect of bending of light beams round the corner was first discovered by Grimaldi (1618-1663).

• We now define diffraction of light as phenomenon of bending of light waves around the corners and their spreading into geometrical shadow.

• Fresnel first explained that the diffraction phenomenon was the result of mutual interference between the secondary wavelets from the same wavefront.

• Thus we can explain diffraction phenomenon using Huygen's principle.

• The diffraction phenomenon is usually divided into two classes
1. Fresnel class of diffraction phenomenon where the source of light and scteen are in general at finite distance from the diffracting aperture
2. Fraunhofer class of diffraction phenomenon where source and the screen are at the infinite distance from the aperture , this is easily achieved by placing the source of light on the focal plane of a convex lens and placing screen on focal plane of another convex lens. This class of diffraction is simple to treat and easy to observe in practice.

• ### Solve out mechanics problems (IITJEE tips and tricks for mechanics)

Hi all here in this article i am giving some tips and tricks to solve problems in mechanics. To master problem solving skill you need to practice more and more problems as said practice makes a man perfect. Look at examples in your text books identify the steps and then try solving out problems on your own.

Motion in a Two dimensional Plane

1. Select a coordinate system and resolve the initial velocity vector into x and y components.
2. Find out acceleration in each direction and solve in each direction according to one rectilinear motion equation.
3. If the acceleration is in vertical direction only.Follow the techniques for solving constant-velocity problems to analyze the horizontal motion. Follow the techniques for solving constant-acceleration problems to analyze the vertical motion. The x and y motions share the same time of flight t.
4. There might be question about trajortory in the Problem ,find out the motion in x and y direction with respect to time from previous point.And then find the value of t from one equation and then put that value in another equation to find out the equation of trajactory

Motion in a Three dimensional Plane
1. Select a coordinate system and resolve the initial velocity vector into x , y and z components
2. Find out acceleration in each direction and solve in each direction according to one rectilinear motion equation.

Uniform Circular Motion
1. Draw a simple, neat diagram of the system.
2. Firstly consider the origin of the forces acting on the each object.To do this find out the field forces acting on the each object.Wherever contact in available account the contact force carefully
3. Find out the force acting on the body.The resultant force should provide the required centrepatal required for Circular motion
4. Centrepatal force=mv2/R will give the velotiy accordingly
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