Numerous times when you would have asked for advice about the important chapters of IIT JEE Physics syllabus, people would have suggested Mechanics, Electricity and Magnetism and so on without blinking once. That advice is not bad, however what most people forget is that Modern Physics is another important unit that is comparatively easier to master than all the other units that are considered important. One thing about IIT JEE is that in the past few years its pattern has changed drastically, and Modern Physics is being given more and more importance with each change.

What is IIT JEE without the tricks it plays with its questions however this is one unit where there isn’t much scope for much twists and turns, thus it is wise to concentrate on it. Use your basic IIT study material to master the concepts (H.C Verma in addition to NCERT books is recommended for concepts of Modern Physics). Follow this up with IIT JEE test series and AIEEE test series, because the questions from this unit would be more and less standardized ones that you can find in any good IIT JEE study material.
The question of discussion is from the chapter Atomic Structure, and goes as follows:
A 12.5 eV electron beam is used to bombard gaseous hydrogen at room temperature. What series of wavelengths will be emitted?
 
The difference in energies would be calculated first by using the formula for energy in nth orbit (-13.6/n2, where n is the number of the orbit) in Hydrogen atom as can be seen in the video. On obtaining the differences it is observed that the electron can go only till the 3rd orbit on excitation. The electron beam would come out as well along with the hydrogen atom because of its increasing Kinetic Energy.
For finding the emitted wavelengths, the Rydberg formula is used and as seen in the video it is observed that 2 lines are from Lyman Series, and 1 from Balmer series.
Practice many such similar problems from IIT JEE test series after mastering the concepts form free IIT study material, because one thing about IIT JEE must always be remembered: It cannot be cracked without a strong conceptual foundation.

 

 

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