What Do You Know About The Speed Of Red And Blue Light (i) In Vacuum, (ii) In Glass? The Refraction Index Of Glass For Blue Light Is 1.665 And For Red Light Is 1.645. (The Speed Of Light In Vacuum Is ).

Why Kaysons ?

Video lectures

Access over 500+ hours of video lectures 24*7, covering complete syllabus for JEE preparation.

Online Support

Practice over 30000+ questions starting from basic level to JEE advance level.

Live Doubt Clearing Session

Ask your doubts live everyday Join our live doubt clearing session conducted by our experts.

National Mock Tests

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.

Organized Learning

Proper planning to complete syllabus is the key to get a decent rank in JEE.

Test Series/Daily assignments

Give tests to analyze your progress and evaluate where you stand in terms of your JEE preparation.



What do you know about the speed of red and blue light (i) In vacuum, (ii) In glass? The refraction index of glass for blue light is 1.665 and for red light is 1.645. (The speed of light in vacuum is ).


Correct option is


(i) In vacuum, the speed of light of all colours (or of all wavelengths) is the same. Hence in vacuum, the speed of both red and blue light is   

(ii) According to wave-theory, the speed of light in glass is given by   


Where c is the speed of light in vacuum (on air) and n is the refractive index of glass. The refractive index of glass for blue light is 1.665. hence the speed of blue light in glass is  


The refractive-index of glass for red light is 1.645. Hence the speed of red light in glass is


Clearly in glass red light travels faster than blue light. 



The equation of the progressive wave is y = 0.5  where yand x are in cm and is in second. What is wave velocity?



The equation of a simple harmonic progressive wave is 


Where y and x are in cm and t in second. Calculate the amplitude, frequency and speed of the wave and the phase difference between two particles at a distance of 2.0 cm apart at any instant. 


The equation of a simple harmonic progressive wave is y = 0.30 sin (314 t– 1.57 x), where tx and y are in second, meter and cm respectively. Calculate the frequency and the wavelength of the wave


The equation of motion of a wave is  where the distances are in metre and the time is in second. Determine the amplitude and the frequency of wave, and the maximum velocity of the particle. What are the velocity and the direction of the wave?


A wave has a speed of 330 metre/second and frequency 500 hertz. The phase difference between two adjacent points is π/3 radian. What will be the path difference between them? 


The equation of a simple harmonic wave is y1 = 0.40 sin (314 t – 1.57 x) meter, and that of another similar wave is y2 = 0.20 sin (314t – 1.57x + 1.57) meter. Find the phase difference between these two waves and the ratio of their intensities. 


In the figure given below is shown displacement-distance (y – x) graph of a transverse wave travelling along a string at the instant t = 0.25 s. At the instant t = 0, the end A of the string was in the mean position. Find out: (i) Frequency, wave-length and velocity of the wave, (ii) Equation of the wave, (iii) Displacement of B at the instant t = 1 second.



A transverse harmonic wave is travelling on a string with a speed of 25 m/s. A particle on the string has maximum velocity and maximum acceleration 4 m/s and 100 m/s2 respectively. What is the waveform?


A wave whose amplitude is 0.07m and frequency is 400 hertz travels in a medium with a velocity of 300 m/s. Determine the displacement equation of oscillation at a distance x metre from the source due to this wave.



(a) The wavelength of a given light is 0.00006 cm. Express this wavelength in micron and in angstrom. 

(b) What will be its wavelength in water, if the refractive index of water be 4/3.