Young’s Double Slit Experiment

Couple

A couple is a special case of a torque with two equal but oppositely directed parallel forces acting at different points of a body.

 

• A couple acts on a rigid body, that is, a body in which none of the internal parts move relative to one another.

• Note 1: We can consider torques about any point between the forces.

• Note 2: Although there is no resultant force, there will be acceleration

Young’s Double Slit Experiment

The initial experiment setup consisted of a candle, as light source, and two sets of pinholes, which produced coherent light waves.

• Light emitted from large source (e.g. light bulb) is not coherent since emission is generally a random process. Each particle emits a “wave burst” at a different time.
• However, light from a point source is coherent. One can produce coherent light by letting light waves pass through a very small opening. The opening acts as a single secondary point source (Huygens principle).
• Laser (Light Amplification by Stimulated Emission of Radiation) sources are coherent as all particles in a material are stimulated to produce wave bursts at the same time

• Light from the same wave front is incident on both slits. The slits become coherent point sources.

• Interference occurs on a distant screen, as alternating bright and dark bands, called fringes.

• The central fringe (q = 0) appears as a result of constructive interference for all wavelengths, therefore it will be white if white light is used.