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JEE-Main, unlike JEE-Advanced, has a fixed exam structure and is not subject to change every year. Up until 2018, the JEE-Main Paper-I was three hours long and consisted of thirty questions in each of the three subjects (physics, chemistry and maths). 4 marks are awarded for correct answers and 1 mark is deducted for incorrect answers.
The number of attempts which a candidate can avail at the examination is limited to three in consecutive years. As of 2018, the top 2,24,000 rankers of JEE-Main will qualify to take the second and final level of examination: JEE-Advanced. this number of 2.24 lakh is not fixed this may vary as per difficulty level of paper of JEE-Main. [7]
The optical path difference between the paths taken by two identical waves can then be used to find the phase change. Finally, using the phase change, the interference between the two waves can be calculated. Fermat's principle states that the path light takes between two points is the path that has the minimum optical path length.
These variations in the refractive index, due to the pressure fluctuations, may be detected optically by refraction, diffraction, and interference effects; [2] reflection may also be used. The acousto-optic effect is extensively used in the measurement and study of ultrasonic waves.
However, with 2022 JEE-Main being postponed from April/May to 20–29 June/21–30 July, JEE-Advanced 2022 was also postponed and subsequently held on 28 August 2022. On 5 November 2024, it was announced by IIT Kanpur , and Joint Admission Board(JAB) that the attempts of JEE-Advanced are now increased from 2 to 3. [ 72 ]
On 7 July 2018, the former Union HRD Minister Prakash Javadekar stated, during a press conference, that the NTA will be holding the Joint Entrance Examination–Main (JEE Main) and the National Eligibility cum Entrance Test-Undergraduate (NEET-UG) twice a year, and will also be holding the National Eligibility Test (NET), the Common Management ...
Because diffraction is the result of addition of all waves (of given wavelength) along all unobstructed paths, the usual procedure is to consider the contribution of an infinitesimally small neighborhood around a certain path (this contribution is usually called a wavelet) and then integrate over all paths (= add all wavelets) from the source to the detector (or given point on a screen).
which is the generalized diffraction grating equation. Here, θ m is the angle of incidence, φ m is the angle of diffraction, λ is the wavelength, and m = 0, 1, 2... is the order of diffraction. Under certain conditions, d m ≪ λ, which can be readily obtained experimentally, the phase term becomes [7] [10]