## Saturday, September 5, 2009

### IIT-JEE-Physics-Revision Questions - Set 3

1. A laser beam λ = 666 nm has a power of 3 mW. Find the pressure exerted on a surface by this beam if the cross sectional area is 3 nm². Assume perfect reflection as normal incidence.

2. A hydrogen-like atom (described by the Bohr model) is observed to emit six wavelengths, originating from all possible transitions between a group of levels. These levels have energies between -0.85 eV and -0.544 eV (including both these values). Find the atomic number of the atom.

Take hc = 1240 eV-nm, ground state energy of hydrogen atom = -13.6 eV.

3. The recoil speed of a hydrogen atom after it emits a photon in going from n = 5 state to n = 1 state is

(a) 2.82 ms-1
(b)4.178 ms-1
(c)8.356 ms-1
(d)6.817 ms-1

4. An electron makes transition inside a hydrogen atom. The orbital angular momentum of the electron may change by

(a) h/2π (b) h/π (c)h/4π (d)h/3π

Multiple options are possible

5. Nuclei of radioactive element A are being produced at a constant rate α. The element has a decay constant λ. At time t = 0, there are N0 nuclei of the element. Calculate the number N of nuclei of A at time t.