question_answer1) What is sky wave propagation?
View Answer play_arrowA ball of superconducting material is dipped in liquid nitrogen and placed near a bar magnet. |
(i) In which direction will it move? |
(ii) What will be the direction of its magnetic moment? |
Sketch the output waveform obtained from NOR gate for the inputs A and B as shown in the figure. |
Input waveform of A and B |
Mohan was crazy for watching World Cup Soccer 2018 final, but he was very much dissatisfied with his present TV set. So he decided to buy a new TV set, he was now confused with different features and functions of the TV sets presently available in the market. He then discussed all the features of digital and analog circuits with his uncle Ranjan, who is an electronic engineer. With his uncle's help, finally he bought a TV to enjoy world cup final. Read the above passage and answer the following questions: |
(i) Which types of signals are better? Show diagrammatic representation of analog and digital signals. |
(ii) What type of nature Ranjan has? |
A radioactive isotope has a half-life of T years. How long will it take the activity to reduce to |
(i) 3.125% |
(ii) 1% of its original value? |
OR |
A neutron is absorbed by \[\text{a}\,\,_{3}^{6}\] Li nucleus with subsequent emission of an alpha particle. Write the corresponding nuclear reaction. Calculate the energy released in this reaction. Given, \[m\,(_{3}^{6}Li)=6.015126\,\,amu\] |
\[m\,(_{2}^{4}He)=4.0026044\,\,amu\] |
\[m\,(_{0}^{1}n)=1.0086654\,\,amu\] |
\[m\,(_{0}^{1}H)=3.016049\,\,amu\] |
Prajapati went to the market to buy some cells for his TV remote. But later on, he felt that those cells were not working properly. So, in order to rectify his doubt, he took those cells to his college's Physics laboratory and checked their emf with the help of potentiometer. |
He was surprised to see that the emf values were less than those printed on the cells by the manufacturer. He then complained the consumer forum regarding this and received the deserving response. |
Read the above passage and answer the following questions. |
(i) What values are displayed by Prajapati? |
(ii) Why does Prajapati especifically used only potentiometer to find out the value of emf of the cells instead of voltmeter. |
A rectangular loop of sides 8 cm and 2 cm with a small cut is moving out of a region of uniform magnetic field of magnitude 0.3 T directed normal to the loop. What is the voltage developed across the cut, if velocity of loop is \[1\text{ }cm{{s}^{-1}}\] in a direction normal to the |
(i) longer side |
(ii) shorter side of the loop For how long does the induced voltage last in each case? |
A network of six identical capacitors, each of capacitance C is made in figure. Find the equivalent capacitance between the points A and B. |
Network of six identical capacitors |
(i) light passes through two polaroids \[{{P}_{1}}\] and \[{{P}_{2}}\] with pass axis of \[{{P}_{2}}\] making an angle, \[\theta \] with the pass axis of \[{{P}_{1}}.\] For what value of \[\theta \] is the intensity of emergent light zero? |
(ii) A third polaroid is placed between \[{{P}_{1}}\] and \[{{P}_{2}}\] with its pass axis making an angle, \[\beta \] with the pass axis of \[{{P}_{1}}.\] Find the value of \[\beta \] for which the intensity of light from \[{{P}_{2}}\] is \[\frac{{{I}_{0}}}{8},\] where \[{{I}_{0}}\] is the intensity of light on the Polaroid \[{{P}_{1}}.\] |
In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \[2\times {{10}^{10}}\] Hz and amplitude 48 V/m. |
(i) What is the wavelength of the wave? |
(ii) What is the amplitude of the oscillating magnetic field? |
(iii) Show that the average energy density of the E field equals the average energy density of the B field. |
Calculate the rate at which the flux linked with the generated area changes with time when a rod of length x is |
(i) translated |
(ii) rotated in a uniform field of induction B as shown in figure. |
Or |
An inductor, L of reactance, \[{{X}_{L}}\] is connected in series with a bulb B to an AC source as shown in the figure. Briefly explain how does the brightness of the bulb change, when |
AC source |
(i) number of turns of the inductor is reduced |
(ii) a capacitor of reactance, \[{{X}_{C}}={{X}_{L}}\] is included in series in the same circuit? |
Ragini was worried about her grand mother who stays all alone in her residence in a crowded area of Varanasi. To ensure safety of her grand mother, she installed a device known as Burglar's alarm under the guidance of her Physics teacher. While doing the experiment, she recorded the following observations. When radiations of frequency \[{{10}^{15}}\] Hz are incident on two photosensitive surfaces A and B, in Burglar's alarm, |
For surface A No photoemission took place. |
For surface B Photoemission took place but photoelectrons have zero velocity. Read the above passage and answer the following questions: |
(i) What are the values displayed by Ragini? |
(ii) Explain the above observations on the basis of Einstein's photoelectric equation. |
A neutron, a proton, an electron and an\[\alpha \text{-particle}\] enter in a region of uniform magnetic field with equal velocities. The magnetic field is directed to the plane of paper. The tracks of the particles are shown in figure. Relate the tracks to particle. |
(i) Why are coherent sources necessary to produce a sustained interference pattern? |
(ii) Describe briefly the formation of diffraction pattern on screen due to a narrow slit illuminated by a monochromatic light. Obtain the condition for angular width of secondary minima. |
An electric field is uniform in the positive X-direction for positive x and uniform with the same magnitude in the negative X-direction for negative x. It is given that |
\[E=200\,\hat{i}\,N{{C}^{-1}}\] for x > 0 |
\[E=-\,200\,\hat{i}\,N{{C}^{-1}}\] for x < 0 |
A right circular cylinder of length 20 cm and radius 5 cm has its centre at the origin and its axis along the X-axis, so that one face is at \[x=+10\text{ }cm\] while other is at \[x=-10\text{ }cm.\] |
(i) What is the net outward flux through each flat face? |
(ii) What is the net outward flux through the cylinder? |
(iii) What is the net charge inside the cylinder? |
Physics teacher Mr. Sharma conducts viva-voce for board practical and asks the following two questions from every student. |
(i) Why a potentiometer be preferred over a voltmeter for the measurement of emf of a cell? |
(ii) Why should a six wire potentiometer be preferred over a three wire potentiometer? The student A who could not answer any question was teacher's ward. However another student B who answered both questions correctly was not teacher's ward. Mr. Sharma awarded full marks to student B. Answer the following questions on the basis of given informations. |
(a) Which values are displayed by Mr. Sharma? |
(b) Figure shows a potentiometer circuit for comparison of two resistances. The balance point with a standard resistor \[R=10\Omega \] is found to be 60 cm, while that with the unknown resistance X is 70 cm. Determine the value of X. What might you do, if you failed to find a balance point with the given cell \[\varepsilon ?\] |
An inductor L, a capacitor C and a resistor R are connected in series in an AC circuit. Deduce with the help of suitable phasor diagram, a mathematical expression for impedance of this circuit. What is meant by resonance of this circuit? Prove that this circuit exhibits resonance at a frequency given by \[1/2\pi \sqrt{LC}.\] |
OR |
(i) A series L-C-R circuit is connected to an AC source of voltage V and angular frequency co when only the capacitor is removed, the current lags behind the voltage by a phase angle \['\phi '\] and when only the inductor is removed, the current leads the voltage by the same phase angle. Find the current flowing and the average power dissipated in the L-C-R circuit. |
(ii) An alternating voltage given by V=140 sin 314t is connected across a pure resistor of resistance 50 Q. Find (a) the frequency of the source (b) the rms current through the resistor. |
(i) How does an unpolarised light incident on a polaroid get polarised? Describe briefly with the help of necessary diagram, the polarisation of light by reflection from a transparent medium. |
(ii) Two polaroids ‘A’ and ‘B’ are kept in crossed position. How should a third polaroid ‘C’ be placed between them, so that the intensity of polarised light transmitted by polaroid B reduces to 1/8 the of the intensity of unpolarised light incident on A? |
OR |
A compound microscope consists of an objective lens of focal length 2,0 cm and an eye piece of focal length 6.25 cm separated by a distance of 15 cm. How far from the objective lens should an object be placed in order to obtain the final image |
(i) At least distance of distinct vision \[(D=25cm)\] |
(ii) At infinity What is the magnifying power in each case? |
Explain the formation of depletion layer and potential barrier in a p-n junction with the help of diagram and also with the help of a labelled diagram, explain the use of p-n junction diode as full wave rectifier. Draw the input and output waveforms. |
OR |
(i) Explain briefly, with the help of a circuit diagram, how V-I characteristics of a p-n junction diodes are obtained in |
(a) forward bias |
(b) reverse bias? |
Draw the shape of the curves obtained. |
(ii) A photodiode is fabricated from a semiconductor with a band gap of 2.8 eV Can it detect wavelength of 6000 nm? Justify. |
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