A 25 watt bulb emits monochromatic yellow light of wavelength of 0.57 μm. Calculate the rate of emission of quanta per second.


Correct option is


Energy emitted by the bulb = 25 watt = 25 J s–1  (∵ 1 watt = 1 Js–1

Energy of one photon (E) = hv   






∴ No. of photons emitted per sec  





Calculate the uncertainty in the velocity of a wagon of mass 3000 kg whose position is known to an accuracy of ±10 pm

(Planck’s constant = 6.63 × 10–34 Js) 


Calculate the uncertainty in the position of an electron if the uncertainty in its velocity is 5.7 × 105 m/sec (h = 6.6 × 10–34 kg m2 s–1, mass of the electron = 9.1×10–31 kg).


A golf ball has a mass of 40 g and a speed of 45 m/s. If the speed can be measured within accuracy of 2%, calculate the uncertainty in position.



If an electron is moving with a velocity 600 ms–1 which is accurate upto 0.005%, then calculate the uncertainty in its position. 

  (h = 6.63 × 10–34 Js, mass of electron = 9.1 × 10–31 kg) 


What is the transition in the hydrogen spectrum would have the same wavelength as the Balmer transition, n = 4 to n = 2 of He+ spectrum?



Calculate the energy required for the process

           He+ (g) → He2+ (g) + e   

The ionization energy for the H atom in the ground state is

 2.18 × 10–18 J atom–1.  


What is the wavelength of the light emitted when the electron in a hydrogen atom undergoes transition from an energy level with n = 4 to an energy level with n = 2? What is the colour corresponding to this wavelength? (Rydberg constant = 109,677 cm–1  


A certain particle carries 2.5 × 10–16 C of static electric charge. Calculate the number of electrons present in it.


An ion with mass number 37 possesses one unit of negative charge. If the ion contains 11.1% more neutrons then the electrons, find the symbol of the ion.    


An ion with mass number 56 contains 3 units of positive charge and 30.4% more neutrons than electrons. Assign the symbol to this ion.