Maximum Marks: 70Marks Time Allowed: 3hours
General Instructions:
(1) All questions are compulsory. There are 33 questions in all.
(2) This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
(3) Section A contains ten very short answer questions and four assertion
reasoning MCQs of 1 mark each, Section B has two case based questions of 4 marks each, Section C contains nine short answer questions of 2 marks each, Section D contains
fiveshortanswerquestionsof3markseachandSectionEcontainsthreelonganswer questions of 5 marks each.
(4) There is no overall choice. However internal choice is provided. You have to attempt only one of the choices in such questions.
Section – A
Sr.No. All questions are compulsory. In case of internal choices, attempt any one of them.
Marks
1 Is electric flux a scalar or a vector? 1
2 Predict the direction of induced current In a metal ring when the ring is moved Toward a straight conductor with constant
speed v. The conductor is carrying a constant current in the direction shown in the figure.
1
3 How does the angle of minimum deviation of a glass prism vary if the incident violet light is replaced by red light?
OR
What are the direction of electric and magnetic field vectors relative to each other and relation to the direction of propagation of electromagnetic waves?
1
4
How does the angular separation of interference fringes changes in Young’s experiment, if the distance between the slits is increased?
1
5 What is the value of angular momentum of electron in the second orbit of Bohr’s model of hydrogen atom?
1 6 In a tropical nuclear reaction e.g. , + → + + 3.27
,although number of nucleons is conserved , yet energy is released. How?
1 v
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7 How does the width of a depletion region of a p-n junction vary if doping concentration is increased?
1 8 In half wave rectification, what is the output frequency if input frequency
is 25 Hz.
1 9 9 State the factors on which the refractive index of a material medium for a
given wavelength depends.
1 11 10 Two lenses of power 3D and -5D are in combination, finf the effective
focal length of this combination.
1 For question numbers 11,12,13and14,two statements are given-one
labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (a), (b), (c) and (d) as given below.
a) Both A and R are true and R is the correct explanation of A b) Both A and R are true but R is NOT the correct explanation of A c) A is true but R is false
d) A is false and R is also false 11
Assertion(A):
A charged particle free to move in an electric field always moves along an electric field line.
Reason(R):
The electric field lines diverge from a negative charge and converge at positive charge.
1
12 Assertion(A):
A parallel plate capacitor is connected across battery through a key. A dielectric slab of dielectric constant K is introduced between the plates. The energy which is stored becomes K times.
Reason(R):
The surface density of charge on the plate remains constant or unchanged.
1
13 Assertion (A):
A ray of light is incident from outside on a glass sphere surrounded by the air. This ray may suffer total internal refraction at the second interface.
Reason (R):
If a ray of light goes from denser to rarer medium, it bends away from the normal.
1
14 Assertion(A):
A convex lens of focal length 30 cm can’t be used as a simple microscope in normal setting.
Reason (R):
For normal setting, the angular magnification of simple microscope is M=D/f
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Section – B
Q Questions 15 and 16 are Case Study based questions and are compulsory. Attempt all 3 sub parts from each question.
15
A group of students while coming from school noticed a box marked “Danger H.T 2200 V” at a substation in the main street.They did not understand the utility of such a high voltage ,while they argued, the supply was only 220 V.They asked their teacher this question the next day.The teacher thought it to be an important question and therefore explained to the whole class.
(a) What device is used to bring the high voltage down to low voltage of A.C current and what is the principle of its working?
(b) Is it possible to use this device for bringing down the high D.C voltage to the low voltage ? Explain
(c) Write the value displayed by the students and the teacher.
4
16 Asha’s uncle was adviced by his doctor to have an MRI( Magnetic Resonance Imaging ) scan of his brain .Her uncle felt that it was too expensive and wanted to postpond it.When Asha learnt about this , she took the help of her family and when she approached the doctor,he also offered a substantial discount .She thus convinced her uncle to undergo the test to enable the doctor to know the condition of his brain. The resulting information greatly helped his doctor to treat him properly. Based on the above paragraph , answer the following questions:
a) What according to you are the values displayed by Asha,her family and Doctor.
b) What in your view could be the reason for MRI test to be so expensive ?
c) Assuming that MRI test was performed using a magnetic field of 0.1 T,find the maximum and minimum values of the force that the magnetic field could exert on a proton (charge = 1.6 × 10 C)that was moving with a speed of 10 / .
44 4
Section – C
All All questions are compulsory. In case of internal choices, attempt anyone.
17
Deduce Coulomb’s law from Gauss’s theorem. OR
A cylinder is placed in a uniform electric field ⃗ with its axis parallel to the field.Show that the total electric flux through the cylinderis zero.
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18 Show mathematically that the potential at a point on the equatorial line of an electric dipole is zero.
2
19 Why does the capacitance of a conductor increase, when an earthed connected conductor is placed near it? Briefly explain.
OR
Three capacitors = 10 , = 5 = 5 are connected to a 6V battery, as shown in fig. Find the charges on the three capacitors.
2
20 If the horizontal component of earth’s magnetic field at a place where the angle of dip is 60 is 0.4 × 10 , calculate the vertical component and the resultant magnetic field at that place.
2
21 Use Biot-Savart law to obtain an expression for the magnetic field at the centre of a coil bent in the form of a square of side 2a currying current .
22 2 22 Arrange the following electromagnetic waves in the order of their
increasing wavelength:
a) γ – rays b) Microwaves c) X- rays d) Radio waves.
What role does infra-red radiation play in maintaining the Earth’s warmth?
22 2
23 A region is illuminated by two sources of light. The intensity at each point is found to be equal to + , where is the intensity of light at the point when source 2 is absent. is similarly defined. Are the sources coherent or incoherent? Explain.
OR
Draw the diagram showing intensity distribution of light on the screen for diffraction of light at a single slit. How is the width of central maxima affected if (i) the width of the slit is doubled; (ii) the wavelength of the light used is increased?
22 2
24 Draw reverse characteristics of a junction diode. Why do we get reverse saturation current?
2
25 An electron and a proton each have the same de-Broglie wavelength. Which one of these has higher kinetic energy? Which one is moving faster?
2 6 V
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OR
Plot a graph showing variation of de-Broglie wavelength versus √ ,where V is accelerating potential for two particles A and B carrying same charge but of masses , ( > ). Which one of the two (A or B) represents a particle of smaller mass and why?
Section -D
Q Questions are compulsory. In case of internal choices, attempt anyone.
26 Two free point charges +4 and + are placed a distance “a” apart. Where should a third point charge q be placed between them such that the entire system may be in equilibrium? What should be the magnitude of q? What type of an equilibrium will it be?
OR
An electric dipole of dipole moment ⃗is placed in a uniform electric field ⃗.Show diagrammatically the orientation of the dipole in the field for which the torque is (i) maximum (ii)half the maximum value (iii) zero.
3
27 A ray of light goes from medium 1 to medium 2. Velocities of light in the two media are respectively. For an angle of incidence in medium 1, the corresponding angle of refraction in medium 2 is /2 .
(i) Which of the two media is optically denser and why? (ii) Establish the relationship between , .
OR
Two monochromatic waves emanating from two coherent sources have the displacements represented by = cos ,and = cos( + ), where is the phase difference between the two displacements. Show that the resultant intensity is given by = 4 ( ) where ∝
.Hence obtain the conditions for constructive and destructive interference.
3
28
Figure shows a rectangular conducting loop PQRS in which arm QR of length “ ” has movable. The loops kept in a uniform magnetic field “B” directed downward perpendicular to the plane of the loop.The arm QR is moved with a uniform speed “ ".
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Deduce the expression for:
(i) the emf induced across the arm “QR”
(ii) the external force required to move the arm, and the power dissipated as heat.
3
29 A 12.9 eV beam of electrons is used to bombard gaseous hydrogen at room temperature. Up to which energy level the hydrogen atoms would be excited? Calculate the wavelength range of Paschen series.
3
30 Draw a circuit diagram of a full wave rectifier. Explain its working principle. Draw the input/output, wave forms indicating clearly the functions of the two diodes used.
3
Section – E
All questions are compulsory. In case of internal choices, attempt anyone.
31 Define the terms (i) ‘cut-off voltage’ and (ii) ‘threshold frequency’ in relation to the phenomenon of photoelectric effect.
Using Einstein’s photoelectric equation show how the cut-off voltage and threshold frequency for a given photosensitive material can be determined with the help of a suitable plot/graph.
OR
(a) Consider two different hydrogen atoms. The electron in each atom is in an excited state. Is it possible for the electrons to have different energies but same orbital angular momentum according to the Bohr model? Justify your answer.
( b) Obtain an expression for the frequency of radiation emitted when a hydrogen atom de-excites from level n to level (n-1).For large n, show that this frequency equals the classical frequency of revolution of the electron in the orbit .
5
P Q
R S
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32 a) Derive the expression for the current flowing in an ideal
inductor and its reactance when connected to an ac source of emf €=€0sinωt.
b) Draw its phasor diagram.
c) If resistance is added in series to inductor what changes will occur in the current flowing in the circuit and phase angle between voltage and current.
OR
In series LCR circuit connected to an ac source of variable frequency and emf €=€0sinωt , draw a plot showing the variation of current ( ) with
angular frequency (ω) for two different values of resistance
( > ).Write the condition under which the phenomenon of resonance occurs. For which value of the resistance out of the two curves, a sharper resonance is produced? Define Q-factor of the circuit and gives its
significance.
5
33
(a) Define fringe width. Calculate the value of fringe width (for bright fringe only) using Young’s double slit experiment, draw required diagram.
(b) Explain two advantages of a reflecting telescope over a refracting telescope.
OR
(a)There are two sets of apparatus of Young’s double slit experiment. In set A, the phase difference between the two waves emanating from the slits does not change with time, whereas in set B, the phase difference between the two waves from the slits changes rapidly with time. What difference will be observed in the pattern obtained on the screen in the two set up’s?
(b) Deduce the expression for the resultant intensity in both the above-mentioned set ups (A and B), assuming that the waves emanating from the two slits have the same amplitude A and same wavelength λ.