If the opening width approaches the wavelength of the light, the diffraction produced becomes more pronounced and the shadow becomes more fuzzy around the edges. The light is diffracted by the thin slit.
Light of wavelength 5.0 x 10 -7 m is used in a Young’s double slit interferometer. The distance between the double slits and the screen is 25 cm. The centre of the third bright fringe is a distance of 5.0 mm from the middle of the central bright fringe in the pattern. What is the separation of the slits?
Light of a certain wavelength produces an interference pattern with bright fringes 2.0 mm apart. The screen is 50 cm from the two slits which are separated by 1.0 x 10 -1 mm. Determine the wavelength of light used.
The emitted light gains in intensity by being reflected many times through the active material which is being stimulated, and then being released from the laser through a partially reflecting end mirror.
The resultant beam is highly monochromatic, coherent, intense and unidirectional.
A large number of equally spaced parallel slits which can also be called an ‘interference grating’. There are two types:
TRANSMISSION : Large number of equally spaced scratches (6000 per cm is common) are inscribed mechanically into a transparent material such as glass. Each scratch becomes an opaque line and the space in between becomes a slit.
Coherent light is directed on the diffraction grating by passing light through a collimator (light gatherer). The pattern can be seen through the telescope. The whole arrangement is called a spectrometer.
The pattern is similar to Young’s double slit pattern. The slits are narrow enough so that diffraction by each of them spreads light over a very wide angle on to a screen. Interference occurs with light waves from all slits.
For a grating, the waves from two adjacent slits will not be significantly out of phase but those from a slit maybe 500 away, may be exactly out of phase. Nearly all the light will cancel out in pairs this way. The more lines, the sharper the peaks will be.
Light from a sodium vapour lamp (m) falls on a grating with 5000 lines per centimetre. Find the angular positions of all the reinforcement positions observed. The wavelength of Sodium vapour (orange light) is 5.98 x 10 -7 metres.
White light containing wavelengths from 400 to 750 nm strikes a grating containing 4000 lines per centimetre. Show that the violet of the third order (m=3) overlaps the red of the second order (m=2) spectrum.