| Kamal and his girlfriend Mira, were at the restaurant. The restaurant was very clean, there were no flies and insects at that place. Mira asked him about the fluorescent UV-lamp presented there at the corner. |
| He explained the importance of that lamp. |
| (i) What values did Kamal show to Mira? |
| (ii) Write down the one natural source of the UV-rays. |
| Give reasons for the following. |
| (i) For ground wave transmission, size of antenna should be comparable to wavelength of signal. |
| (ii) Audio signals converted into an electromagnetic wave, are not directly transmitted as such. |
| (iii) The amplitude of modulating signal is kept less than the amplitude of carrier wave. |
| Kanchan and Mansi students of class XIIth, were assigned a project based on magnetism. In their project work, they had calculate the value of earth's magnetic field. When they submit their project work for verification, Mr. Sanjay Sharma, their Physics teacher corrected the mistakes. He also suggested, few books which were useful to them. |
| (i) What values did Mr. Sanjay Sharma exhibit towards their students? |
| (ii) Mention the three magnetic elements regarding the earth's magnetic field and draw the related diagram. |
| On a field Ram and Shyam were playing football. Suddenly, a player kicked out the ball outside the field and the ball reached an electric power substation. One of the players was planning to go and bring back the ball to the field but, Ram and Shyam stopped him saying that it is dangerous to go to the substation as warmed up body can be caught by the strong magnetic field, which is created by high voltage current in conduction of the switch yard and that may result in death. |
| (i) Ram and Shyam are the students of class 12. What values do you infer from the character of Ram and Shyam? |
| (ii) A current is set-up along a hollow copper pipe. Is there magnetic field |
| (a) inside? |
| (b) outside the pipe? |
| Determine the potential difference across the plates of the capacitor C i of the network shown in the figure. (Assume, \[{{E}_{2}}>{{E}_{1}}\]). |
|
| OR |
| A 600 pF capacitor is charged by a 200 V supply. It is then disconnected from the supply and is connected to another uncharged 600 pF capacitor, How much electrostatic energy is lost in the process? |
| The value of ground state energy of hydrogen atom is -13.6 eV. |
| (i) What does the negative sign signify? |
| (ii) How much energy is required to take an electron in this atom from the ground state to the first excited state? |
| It is desired to supply a current of 2A through a resistance of \[10\,\Omega .\] 20 cells are provided, each of them has 2V emf and internal resistance of \[0.5\,\Omega .\] Two students of class XIIth, Shikha and Shahana try their hand on the requirement. Shahana succeeds but Shikha not. |
| (i) Justify the set up of Shahana. |
| (ii) What might have gone wrong with Shikha, when she gets 12 A current in the load? |
| (iii) What are the basic values shown by Shahana and Shikha in their work? |
| (i) Compute the equivalent resistance of the network. |
| (ii) Obtain the voltage drops \[{{V}_{AB}}\] and \[{{V}_{CD}}.\] |
| (i) What is the net electric field on the C1 atom due to eight Cs atoms? |
| (ii) Suppose that the Cs atom at the corner A is missing. What is the net force now on the C1 atom due to seven remaining Cs atoms? |
| A man with normal near point (25 cm) reads a book with small print using a magnifying glass of a thin convex lens of focal length 5 cm, |
| (i) What is the closest and the farthest distance at which he should keep the lens from the page, so that he can read the book when viewing through the magnifying glass? |
| (ii) What is the maximum and the minimum angular magnification (magnifying power) possible using the above simple microscope? |
| A glass prism of refracting angle \[60{}^\circ \] and refractive index 1.5, is completely immersed in water of refractive index 1.33. Calculate the angle of minimum deviation of the prism in this situation. |
| \[(given,si{{n}^{-1}}0.56=34.3{}^\circ )\] |
| Or |
| (i) The refractive indices of crown glass for red and violet colours are 1.515 and 1.523 respectively. Find the dispersive power of crown glass between these colours. |
| (ii) If a crown glass prism produces a mean deviation of \[40{}^\circ ,\] what will be the angular dispersion? |
(Given, \[{{\mathbf{V}}_{\mathbf{1}}}\mathbf{<}{{\mathbf{V}}_{\mathbf{2}}}\mathbf{<}{{\mathbf{V}}_{\mathbf{3}}}\mathbf{<}{{\mathbf{V}}_{\mathbf{4}}}\]) The four equipotential surfaces are shown in the figure. Draw the corresponding electric field lines for the given pattern of the equipotential surfaces. Also, state the region in which the electric field intensity is more, | In a plot of photoelectric current versus anode potential, how does |
| (i) the saturation current vary with anode potential for incident radiations of different frequencies but same intensity? |
| (ii) the stopping potential vary for incident radiations of different intensities but same frequency? |
| (iii) photoelectric current vary for different intensities but same frequency of incident radiations? |
| Justify your answer in each case. |
| Disha's younger sister Divya watching coloured soap bubbles and eagerly asked her elder sister Disha, why it happens? Disha is a student of class XIIth and explained that phenomenon to her sister. |
| (i) What values did Disha show to her? |
| (ii) Name the phenomenon involved in coloured appearance of the bubbles. |
| (iii) Explain that phenomenon. |
| A 1 m long conducting rod rotates with an angular frequency of 400 rad \[{{s}^{-1}}\] about an axis normal to the rod passing through its one end. |
| The other end of the rod is in contact with a circular metallic ring. A constant magnetic field of 0.5 T parallel to the axis exists everywhere, |
| Find an expression for the emf induced between the centre and the ring and then calculate the value of induced emf from the given data, |
| Or |
| A circuit containing a 80 m H inductor and a \[60\,\mu F\] capacitor in series is connected to a 230 V 50 Hz supply. The resistance of the circuit is negligible. |
| (i) Obtain the current amplitude and rms values. |
| (ii) Obtain the rms values of potential drops across each element. |
| (iii) What is the average power transferred to the inductor? |
| (iv) What is the average power transferred to the capacitor? |
| (v) What is the average power absorbed by the circuit? |
| Light consisting of two wavelengths 400 nm and 560 nm is incident normally on Young's double slit of separation 0.1 mm. An interference pattern is formed on the screen placed 1.0 m from the slits. Calculate the separation between successive regions of total darkness. |
| Or |
| Find an expression for the linear width of central maxima in diffraction pattern obtained from a single slit. Also, draw a graph of intensity distribution pattern on the screen. |
| (i) what will be the forward current at a forward voltage of 0.6V? |
| (ii) what will be the increase in the current, if the voltage across the diode is increased to 0.7V? |
| (iii) what is the dynamic resistance? |
| (iv) what will be the change in current, if reverse bias voltage changes from 1V to 2V? |
| Or |
| (i) Give some practical application of LED. Explain, why the semiconductor used for fabrication of visible light LEDs must have a band gap of at least (nearly) 1.8 eV |
| (ii) Draw a circuit diagram and show the biasing of a light emitting diode (LED). Give its two advantages over conventional incandescent lamps. |
| (iii) Draw energy band diagram of n-type and p-type semiconductor. |
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