Set 1 kho tài liệu bách khoa

C.B.S.E Examination Papers — 2003 OUTSIDE DELHI SET – I Write the S.I unit of (i) electric field intensity and (ii) electric dipole moment What are superconductors ? Name the temperature for a thermocouple, at which its (i) thermo emf changes sign, (ii) thermoelectic power becomes zero What should be the orientation of a magnetic dipole in a uniform magnetic field so that its potential energy is maximum? An object is placed at the focus of a concave lens Where will its image be formed? Two point charges qA = +3 µ C and qB = – µ C are located 20 cm apart in vacuum (i) Find the electric field at the mid point of the line AB joining the two charges (ii) If a negative test charge –9 of magnitude 1.5 × 10 C is placed at the centre, find the force experienced by the test charge What is a button cell? Name any two types of button cells Or Write the equations for chemical reactions taking place at the (i) anode and (ii) cathode of a lead accumulator during its charging In a given circuit, inductor L and resistor R have identical resistance Two similiar electric lamps B1 and B2 are connected as shown When switch S is closed, (i) which one of the lamps lights up earlier, (ii) will the lamps be equally bright after some time ? Justify your answer S Chand & Company Limited 10 11 12 13 14 Explain with an example, whether the nuetron-proton ratio in a nucleus increases or decreases due to beta (β) decay Name the gate obtained from the combination of gates shown in the figure Draw its logic symbol Write the truth table of the combination How is a p-type semiconductor formed? Name the major charge carriers in it Draw the energy band diagram of a p-type semiconductor What is an ‘analog signal’ and a ‘digital signal’? How can an analog signal be converted into a digital signal ? Are the paths of electrons straight lines between successive collisions (with positive ions of the metal) in the (i) absence of electric field (ii) presence of electric field? Establish a relation between drift velocity ‘vd’ of an electron in a conductor of cross-section ‘A’, carrying current ‘i’ and concentraion ‘n’of free electrons per unit volume of conductor Hence obtain the relation between current density and drift velocity Six resistors, each of value Ω, are joined together in a circuit as shown in the figure Calculate equivalent resistance across the points A and B If a cell of emf 2V is connected across AB, compute the current through the arms AB and DF of the circuit S Chand & Company Limited 15 16 17 18 19 20 Drive an expression for the force acting on a current carrying conductor placed in a uniform magnetic field Name the rule which gives the direction of the force Write the condition for which this force will have (i) maximum, (ii) minimum value Where on the earth’s surface is the value of vertical component of the earth’s magnetic field zero ? –4 The horizontal component of the earth’s magnetic field at a given place is 0.4 × 10 Wb/m and angle of dip is 30° Calculate the value of (i) vertical component, (ii) the total intensity of the earth’s magneitc field A pure inductor is connected across an a.c source Show mathematically that the current in it lags behind the applied emf by a phase angle of π/2 What is its inductive reactance? draw a graph showing the vriation of inductive reactance with the frequency of the a.c source Or An alternating emf is applied across a capacitor Show mathematically that current in it leads the applied emf by a phase angle of π/2 What is its capacitive reactance? Draw a graph showing the variation of capacitive reactance with the frequency of the a.c source A town situated 20 km away from a power plant generating power at 440V, requires 600 kW of electric power at 220 V The resistance of the two wire line carrying power is 0.4 Ω per km The town gets power from the line through a 3000 – 220 V step down transformer at a substation in the town (i) Find the line power losses in the form of heat (ii) How much power must the plant supply, assuming there is negligible power loss due to leakage? What is a wave front? What is the geometrical shape of a wave front of light emerging out of a convex lens, when point source is placed at its focus? Using Huygens’ principle show that, for a parallel beam incident on a reflecting surface, the angle of reflection is equal to the angle of incidence Two slits in Young’s double slit experiment are illuminated by two different lamps emitting light of the same wavelenegth Will you observe the interference pattern? Justify your answer S Chand & Company Limited 21 22 Find the ratio of intensities at two points on a screen in Young’s double slit experiment, when waves from the two slits have path difference of (i) 0, (ii) λ/4 A converging lens of focal length 6.25 cm is used as a magnifying glass If the near point of the observer is 25 cm from the eye and lens is held close to the eye, calculate (i) the distance of the object from the lens, (ii) the angular magnification (magnifying power) Also find the angular magnification (magnifying power) when the final image is formed at infinity Draw a graph to show the variation of the angle of deviation ‘D’ with that of the angle of incidence ‘i’ for a monochromatic ray of light passing through a glass prism of refracting angle  D + A sin  m    µ= ‘A’ Hence deduce the relation  A sin   2 23 24 25 26 Draw a labelled diagram of a common base amplifier using a p-n-p transistor Define the term ‘voltage gain’ and write an expression for it What are inferior planets? Give an example of an inferior planet Describe Copernicus method to determine the distance of an inferior palnet from the Earth Give the principle of working of a Van de Graff generator With the help of a labelled diagram, describe its construction and working How is the leakage of a charge minimised from the generator? Or Obtain the expression for the capacitance of a parallel plate capacitor Three capacitors of capacitances C1, C2 and C3 are connected (i) in series, (ii) in parallel Show that the energy stored in the series combination is the same as that in the parallel combination A schematic arrangement for transmitting a message signal (20 Hz to 20 kHz) is given below: S Chand & Company Limited 27 Give two drawbacks from which this arrangement suffers Describe briefly with the help of a block diagram the alternative arrangement for the transmision and reception of the message signal Derive the expression for the de Broglie wavelength of an electron moving under a potential difference of V volt Describe Davisson and Germer experiment to establish the wave nature of electrons Draw a labelled diagram of the apparatus used ANSWERS –1 (i) newton/coulomb (NC ) (ii) Coulomb-metre (Cm) See Ans 24, Page 74 (i) Temperature of inversion; (ii) Neutral temperature The magnetic dipole moment vector must be opposite to the magnetic field vector 1 fu − = ⇒ v = v u f f +u Let the focal length be x Then with proper sign, (− x ) (− x ) x = − v= −x − x Thus the image is formed at half the focal length from the lens, on the same side as the object S Chand & Company Limited (i) Fields at the midpoint due to both the charges are equal and are directed towards B Therefore, the resultant field is E =2 kq A r2 = × × 10 × × 10 −6 (0.1)2 = 3.6 × 10 N/C , directed towards B (ii) Force experienced by the negative test charge has the magnitude F = qE = 1.5 × 10 −19 × 3.6 × 10 = 5.4 × 10−3 N It is directed towards A See Ans 88, Page 119 Or See Ans 69, Page 116 (i) Bulb B2 lights up earlier because induced emf in the inductor delays the growth of current in B1 (ii) When the study state is reached, the inductor plays no role and so both the bulbs will become equally bright Beta decay : A ZX → A Z + 1Y + − 1e neutron-proton ratio in X = A− Z Z neutron-proton ratio in Y = A − ( Z + 1) Z +1 Thus the neutron - proton ratio decreases due to β-decay S Chand & Company Limited 10 11 12 13 NOR Gate See Ans 65, 66, Page 368 See Ans Page 362 & Ans 32, 33, Page 365 See Ans 2, 3, Page 380 Conversion of analog signal into digital signal : This requires the following steps : (i) Sampling : See Ans 28, Page 383 (ii) Quantization : This is process of dividing the maximum value of an analogue signal into a fixed number of levels, in order to convert the pulse amplitude modulated signal into a binary code (i) Yes; (ii) No Relation : See Ans 1, Page 82 I = ne v d A The upper part of the network is a balanced Wheatstone brige Therefore, the resistor between F and D can be ignored The equivalent circuit becomes Current density = 14 Equivalent resistance is given by or 1 1 = + + = R 8 R = 2Ω S Chand & Company Limited = 1A Current through DF = zero Force on a Current Carrying Conductor in a Magnetic field In a conductor the current is due to the motion of free electrons As a magnetic field exerts a force on a moving charge, so there is a force on the free electrons drifting in the conductor and hence on the conductor as a whole The force f on an electron is f = Be v sin θ " !" where v is the drift velocity and θ is the angle between the directions of B and v If A is the area of cross-section of the conductor and n is the electron density, then the total number of free electrons in the conductor at any instant is nAl Therefore, the total force on the conductor is Current through AB = 15 F = (nAl ) f = nAlBev sin θ = B (nAev )l sin θ Since nAev = I, we have F = BI l sin θ Direction of this force is given by Fleming’s left hand rule: Stretch the index finger, the central finger and the thumb of the left hand mutually perpendicular If the index finger points in the direction of the field and the central finger in the direction of current, then the thumb points in the direction of force Force is maximum when θ = 90° ; F max Force is minimum when θ = 0° ; F = BI l = zero S Chand & Company Limited 16 BV is zero at the magneitic equator Numerical (i) BV = BH tan δ = 0.4 × 10 −4 × tan 30° = 2.3 × 10 −5 Wb/m (ii) B = 17 18 BH 0.4 × 10 −4 = = 4.6 ×10 −5 Wb/m cos δ cos 30° See Ans 83, Page 230 & Ans 48, Page 227 Or See Ans 84, Page 231 & Ans 48, Page 227 (i) Total length of the wire = × 20 = 40 km Resistance of the wire = 0.4 × 40 = 16 Ω P 600 × 10 = = 200 A 3000 V 2 Power loss = I R = (200) × 16 = 640 × 10 W = 640 kW (ii) Power to be supplied by the plant = 600 + 640 = 1240 kW 19 See Ans 1, Page 261 & Ans 88, Page 267 The wavefront emerging out of the convex lens is plane 20 No, because the sources are not coherent Numerical : Current I = Resultant intensity I µ cos ( φ / ) S Chand & Company Limited cos ( φ1 / ) I1 = I2 cos ( φ / ) ⇒ φ2 = Here φ1 = 0, 2π  λ  π   = So, λ 4 I1 = =2 I2 cos ( π / ) 21 (i) 1 − = v u f = ⇒ u = fv f−v 6.25 × ( −25 ) 6.25 − ( −25 ) =− 6.25 × 25 = − cm 31.25 (ii) Angular magnification when the image is formed at the least distance of distinct vision =1+ D 25 =1+ =5 f 6.25 D 25 Angular magnification when the image is formed at infinity = f = 6.25 = S Chand & Company Limited 22 23 24 25 26 27 See Ans 35, Page 290 & Ans 103, Page 301 See Ans 74, Page 369 Out of course See Ans 13, Page 34 The leakage of charge is minimized by making the generator perfectly spherical, thus avoiding sharp points Or See Ans 10, Page 32 Drawbacks (i) Audio frequencies cannot be efficiently radiated and cannot be transmitted over long distances (ii) Simultaneous transmission by different transmitters can cause confusion at the receiver end due to overlapping of frequencies Alternative arrangement: In order to overcome these difficulties, the audio signal is superimposed on high frequency radiowave before transmission, with the help of a modulator The signal is recovered at the receiver with the help of a demodulator Different transmitting stations are allotted different frequency carrier waves and a single receiver can tune into these transmitters without any overlap See Ans 1, ; Pages 328, 329 S Chand & Company Limited ... kq A r2 = × × 10 × × 10 −6 (0 .1) 2 = 3.6 × 10 N/C , directed towards B (ii) Force experienced by the negative test charge has the magnitude F = qE = 1. 5 × 10 19 × 3.6 × 10 = 5.4 × 10 −3 N It is... Z + 1Y + − 1e neutron-proton ratio in X = A− Z Z neutron-proton ratio in Y = A − ( Z + 1) Z +1 Thus the neutron - proton ratio decreases due to β-decay S Chand & Company Limited 10 11 12 13 NOR... Chand & Company Limited 16 BV is zero at the magneitic equator Numerical (i) BV = BH tan δ = 0.4 × 10 −4 × tan 30° = 2.3 × 10 −5 Wb/m (ii) B = 17 18 BH 0.4 × 10 −4 = = 4.6 10 −5 Wb/m cos δ cos