• # question_answer Direction: For the following questions, choose the correct answers from the codes [a], [b], [c] and [d] defined as follows Statement I An ideal black body always appears black irrespective of me temperature of the black body. Statement II An ideal black body absorbs all the radiations falling on it and no radiant energy has been reflected. A)  Statement I is true. Statement II is also true and Statement n is the correct explanation of Statement I. B)  Statement I is true. Statement II is also true and Statement II is not the correct explanation of Statement I. C)  Statement I is true. Statement II is false. D)  Statement I is false. Statement II is true.

Statement II is correct and because of this only the black body appears black but if the temperature of black body is very high than it would be self-luminous and won't appear black. Direction: A plate was cut from a quartz crystal and is used to control the frequency of an oscillating electrical circuit. Longitudinal standing waves are set up in the plate with displacement antinodes at opposite faces. The fundamental frequency of vibration is given by the equation of ${{f}_{0}}=\frac{2.87\times {{10}^{4}}}{s}$${{f}_{0}}$ is n Hz and s is the thickness of plate in cm. Face area of the plate is 50 cm2, density of quartz is 2660 kg/m3. Based on above information, answer the following questions: