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Physics mock paper I 2016-17

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Udayan Sathe
Mumbai University (MU), Mumbai
Msc and M.Ed physics

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Physics mock paper I 2016-17 Section I Question 1 a) Find the weight of a body of mass 15 kg. Also, calculate the force acting on it. b) Explain, how two agents doing the same work have different powers. c) What is the function of the split ring in a d.c. motor ? d) What is the effect on the kinetic energy of a moving car if (i) mass is doubled. (ii) its velocity is halved ? e) Draw a labeled diagram to illustrate the working of an optical fibre and mention two uses. Question 2 a) Give the difference between forced vibration and resonance. b) Why is it not advisable to wear damp clothes ? c) The specific latent heat of fusion of lead is 5.9 kcal/kg. A block of lead at its melting point needs 177 kcal of heat for complete melting. What is the mass of the lead ? d) list the factors and how they effect the internal resistance of a cell. e) Water in an electric kettle connected to a 220 V supply took 5 minutes to reach its boiling point. How long would it have taken if the supply had been of 200 V ? Question 3 a) Give the principle of operation of a D.C. motor. Also, state the energy changes that take place in it. b) Name the process responsible for the energy generation in the sun. Give a representative equation for this process. c) State two differences each between a D.C moter and an A.C. generator. d) i) Write specific heat capacity of water. ii) 1 calorie is equal to _______. e) What are damped vibrations ? Question 4 a) In a three pin plug, how would you identify the earth pin ? In which connecting wire should a switch be connected ? b) List the radiations in the order of their increasing frequencies, which make up the complete electromagnetic spectrum. c) A 9 volt battery has a capacity of giving 60 amperes of current for 1 hour. How long can the battery keep a 60 W lamp on ? d) State the factors on which the heat absorbed by a body depends. e) What are thermionic emissions ? Section II (Answer any four questions) Question 5 a) A body of mass 10 kg is moving with a velocity of 15 m/s When a force is applied on it, its velocity becomes 35 m/s after 10 sec. Calculate the applied force. b) What kind of energy is possessed by a body in the following case (i) moving bullet (ii) a pinning top c) Draw a neat diagram of a pulley system having a velocity ratio 5. If the above pulley system is 75% efficient and lifts a load of 2000 N, find the effort required. Question 6 a) An immersion heater having a resistance 60 is connected to a 220 V mains. How much time would be required to heat 2 kg of water from 30 C to 100 C. b) Give three characteristics of image formed by a concave lens. c) Write any two advantages of Ring system. Question 7 a) The diagram below shows an object OA and its image IB formed by a lens. Complete the ray diagram and locate the focus of the lens by labeling correctly. State the type of the lens used. b) c) Give three uses of infrared radiations. What is the function of the following in a directly heated diode valve : Question 8 a) A ray of light is incident on the face AB of a glass prism as shown. i) show the path of light within the prism and out of it. ii) Name the prism. iii) At what angle of incidence does this ray strike the face AC ? b) c) Explain with reference in refraction effect : i) Mirage ii) Looming Does the apparent depth of a tank of water change, normally ? Question 9 a) What is meant by the term i) echo ii) reverberation. b) State the energy changes in the following : i) the sun ii) electric bell iii) steam engine iv)electric cell c) Why are infrared radiations used for photography in fog ? Question 10 a) i) State the SI unit of (1) electric power and (2) electrical energy. ii) A lamp is rated 40 W, 250 V. Calculate the current flowing through the lamp. b) i) Give two precautions that you would take while putting off an electric switch. ii) An electric heater is rated 220 V, 550 W. 1. What does this statement mean ? 2. Calculate the electrical energy consumed in 3 hours. 3. Electric energy is also measured in kWh. What do you understand by a kilowatt-hour ? Physics Answer :-1 a) W = mg = 15 x 10 = 150 N F = mg = 150 N Force acting on the body = weight of the body b) Power = W/t, the two agents can have different powers to do the same work if they take different amounts of time. c) The split ring acts as a commutator. The direction of the current through the coil is reversed after every half rotation so that the direction of the rotating couple remains unchanged and coil continues to rotate in the same direction. d) i) K.E.= mv2 If mass is doubled, K.E. gets doubled. ii) If velocity is halved, the K.E. becomes one fourth. e) 1] Communication 2] Medical endoscopy etc. Answer : 2 a) When an oscillatory system is made to oscillate under the action of an externally applied periodic force, it is said to execute a forced vibration. Resonance is a special case of forced vibration. In this case; the externally applied periodic force has the same frequency as the natural frequency of oscillation of the given oscillatory system. b) The water content in the damp clothes evaporates rapidly taking latent heat from the body for vapourizing. This causes over cooling. The chill lowers the resistance of the body to colds and fever. c) d) e) H = mL m = H = 177 = 30 kg L 5.9 The internal resistance of a cell depends on 1] nature, concentration and temperature of the electrolyte. 2] surface area of the dipped part of the electrode. 3] distance between the electrolyte. V1 = 220 V; t1 = 5; t2 = x; R = Constant for the same kettle; V2 = 200 V H = V2t V21t1 = V22t22 R R R i.e. 220 x 220 x 5 = 200 x 200 x 220 x 220 x 5 = 200 x 200 22 x 11 x 5 = 200 1210 = 200 6.05 min = Answer :- 3 a) The principle of operation of a D.C. motor is that when a current carrying coil is placed in a magnetic field, it experiences a torque that tends to rotate it. In a D.C. motor electrical energy to mechanical energy. b) The process responsible for the energy generation in the sun is the process of nuclear fusion. 411H 42He + 201e + energy c) D.C. Motor A.C. Generator 1. Converts electrical energy to mechanical 1. Converts mechanical energy to energy. electrical energy. 2. Uses split ring commutator. 2. Uses pair of slip rings. d) i) 4.2 J g-10C-1. ii) 4.2 joules. e) The periodic vibrations of continuously decreasing amplitude are called damped vibrations, e.g., oscillation of a simple pendulum in air. Answer : 4 a) The earth pin is thicker and longer. The switch should always be connected to the live wire. b) Radio waves (107 Hz) < Microwaves (1011 107) < Infrared (3.7 x 1017 1011) < Visible light (7.5 x 1014 3.7 x 1014) < Ultraviolet (1016 7.5 x 1014) < X-rays (1010 1016) < Gamma rays (1024 1019). c) d) Energy released by battery in 1 hr. E=VxIxt = 9 x 60 x 1 = 540 Wh E = Pxt E =t P T = 540 = 9 hrs. 60 i) Mass of the body. ii) Increase in temperature. iii) Specific heat capacity of the body. e) It is the process by which electrons are ejected out from the surface of a metal by heating that metallic substance or surface. SECTION II Answer :- 5 a) Final velocity = 35 m/s, initial velocity u = 15 m/s, t = 10 seconds. a= -u t a = 35-15 = 20 = 2 m/s2 10 10 F = m x a = 10 x 2 = 20 N. b) i) Kinetic energy c) V.R. = 5 = 75 , L = 2000 N 100 = M.A. V.R. 75 = M.A. 100 5 M.A. = 375 = 3.75 100 Also, M.A. = L E 3.75 = 2000 E E = 533.33 N ii) Kinetic energy Answer 6 :a) I = V = 240 = 4A R 60 Let t be the time required. Heat required = Heat produced mC = I2Rt 2 x 4 x 103 x (100 30) = 42 x 60 x t 2 x 4 x 103 x 70 = t 4 x 4 x 60 560000 = t 960 t = 583.3 sec = 9.72 min. b) Virtual, erect and diminished. c) 1] Reduces cost of wiring. 2] In installing a new appliance, a new line upto the distribution box is not required. Appliance can easily be connected to the ring, main in the room. 3] Plugs and sockets of the same size can be used. Answer 7 :a) Lens used is convex, Image is real, inverted and magnified. b) 1. They are used in the photography at night or in fog because they are not scattered much. 2. They are used as signals during war because of their long wavelengths and less scattering, the actual signal does not change its direction. 3. Photographic dark rooms are provided with infrared lamps since they do not affect the ordinary photographic film. c) i) Plate cylinder connected to positive of high tension battery. It attracts thermions from the cathode cylinder. ii) Cathode cylinder is coated with oxides of alkali metals and absorbs thermions on absorbing heat energy from the filament. iii) Filament is connected to low tension battery. It provides necessary heat energy so that the cathode cylinder can emit thermions. Answer 8 :- a) i) This is a right angled isosceles prism called a totally reflecting prism. ii) Angle of incidence at face AC = 45 . b) i) Mirage It occurs when the hot air near the surface causes the light rays to bend upwards when a beam of light travels from the top of a tree it suffers successive refraction as it enters a medium of progressively low density and ultimately reaches the stage when i, becomes greater than critical angle between the two layers. The light suffers total internal reflection and is returned into the same medium. When the reflected beam enters the eye of the observer it appears as if an inverted image of the object is formed on the same giving an impression of presence of water. ii) Looming It occurs when colder air near the surface causes light rays to bend downwards. In cold region the lower layer of air are cooled so much that its density increases downwards. Rays from distant object bend more and more away from the normal and suffer total internal reflection and ultimately appear to be emanating from an object hanging inverted in the sky. c) When viewed normally Snell s law fails and hence no refraction takes place, i.e., depth remains the same. Answer 9 :a) i) Echo the phenomenon due to which a reflected sound is heard after reflection from a distant rigid object after the original sound dies off is called an echo. ii) Reverberation When a series of echoes falls on the ear from various reflections one after another, thereby forming a continuous rolling sound is called reverberation. b) i) Nuclear energy ii) Electrical energy iii) Heat energy iv) Chemical energy heat and light energy sound energy mechanical energy electrical energy c) Infrared radiations are used because they are not scattered by mist or fog and can penetrate appreciably through it. Answer ;- 10 a) i) 1] Watt and 2] Kilowatt hour or joule. ii) P = VI I = P = 40 = 0.16 A V 250 b) i) We will make sure that no naked wire is touching the button of the switch and neither the hand nor the switch is wet. ii) 1] The statement means that the heater should be connected to 220 V supply and it consumes 550 W power. 2] Energy consumed in 3 hr. = 550 x 3 = 1.65 kWh 1000 = 1.65 x 3600 = 5940 kJ 3] It is the energy consumed in a resistor when the potential difference is 1 V and 1 A current flows for 1000 hours. Physics Answer 1:A] W = FS cos F = 30 N; S = 10 m; = 60 hence cos 60 = W = 30 x 10 x W = 150 J B] F = m x g = 10.5 x 10 = 105 N. This is also the weight of 10.5 kg mass. C] i. M.A. is always less than 1 as effort arm is always smaller than load arm. ii. It is called a speed multiplier as load moves through a larger distance as compared to effort. D] By placing the concave lens in the path of a converging beam, a real image can be obtained. E] The frequency of 3.6 m wave is lesser than that of the 1.8 m wave. Hence, the sound would be more flat and dull. Answer 2 :A] Dispersion of light is the phenomenon due to which a ray of white light on passing through a prism splits into seven colours.

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