Sample Paper – 2013
Class – XII
Subject – Physics
Time Allowed : 2 hours Maximum Marks : 70
Dual nature and Atomic nucleus (a) All questions are compulsory (b) Question numbers 1 to 8 are very short answer type questions, carrying one mark each. (c) Question numbers 9 to 18 are short answer type questions, carrying two marks each. (d) Question numbers 19 to 27 carry three marks each. (e) Question numbers 28 to 30 are long answer type questions, carrying five marks each. (f) Use of calculators is not permitted. However, you may use log tables, if necessary. Q.1> With what purpose was the Davisson and Germer experiment performed. Q.2> Briefly explain hertz’s observation regarding Photo-emission? Q.3> What was Hallwach’s observation? What was Lenard’s observation regarding Photo-emission? Q.4> Draw a graph showing the variation of stopping potential as a function of frequency. What are the two main implications of this graph. Q.5> Find the De’Broglie wavelength of an electron accelerated by 50 volts. Q.6> What was the drawback ofRutherford’s model? Q.7> A material has a threshold frequency fo. What would be the stopping potential if light of frequency f is incident on it. What basic condition must be satisfied for the emission to take place. Q.8> Plot a graph showing the variation of number of scattered particles as a function of scattering angle for rutherford’s experiment. Q.9> Light of frequency 6 x 1014 Hz has a power of 2mW. What is the energy of the photon? How many photons are emitted by the source in one second. Q.10> A proton and an electron have the same De’Broglie wavelength. Which of them will have smaller kinetic energy. Q.11> Mention 3 ways by which an electron can be removed from a material. Q.12> Mention 4 laws of photo-emission. Q.13> When light of wavelength 620nm falls on a material, the stopping potential is found to be 0.5eV. What will be the stopping potential if light of wavelength 310 nm falls on the same material. Q.14> Draw an energy level diagram to depict various spectral series. Q.15> Mention 3 conclusions ofRutherford’s experiment. Q.16> An alpha particle having 7.7MeV is fired into a gold foil. Find the distance of closest approach if atomic number of gold is 79. Q.17> Give 2 reasons to show that the wave theory in insufficient to explain the photo-electric effect. Q.18> Mention 2 drawbacks of the Bohr’s model. Q.19> A hypothetical atom has a muon with the same charge but mass 207 times that of electron, revolving around a proton. Assuming Bohr’s theory to be valid, find the value of first bohr radius and ground state energy. Q.20> A 10kg satellite revolves around the earth every 2 hours in an orbit of radius 8000km. Assuming Bohr’s theory to be valid for this system, find the quantum number of its orbit. Q.21> De’Broglie said that an electron in the nth shell, completes exactly n wavelengths during one rotation. Using this data, show that the angular momentum of the electron is quantized. Q.22> State the three postulates of Bohr’s theory. Q.23> Hydrogen gas is bombarded with 12.5eV electron beam. What series of wavelengths will be emitted. Q.24> What are photons. Mention 3 properties. Q.25> Chlorine has two isotopes having masses 34.98 u and 36.98 u. The relative abundance of these isotopes is 75% and 25%. What is the atomic mass of chlorine. Q.26> What are isobars and isotones. Give 2 examples of each. Q.27> Show that the nuclear density is independent of mass number. What is its value? Q.28> Draw the binding energy curve and mention 4 conclusions. Q.29> What are nuclear forces? Mention 2 properties and plot the variation of potential energy. Q.30> Derive the radioactive decay law and prove that (a) Activity of a sample is proportional to the concentration (b) Rate of change of activity is inversely proportional to the square of half life.