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P510/2 PHYSICS JULY 2012 Paper2 1 2 hrs 2 GAYAZA HIGH SCHOOL S.6 MOCK EXAMINATIONS PHYSICS PAPER 2 2HOURS 30MINUTES INSTRUCTIONS TO CANDIDATES Attempt five questions altogether. Attempt only one question from section A and B. Do not attempt more than two questions from section C and D. Assume where necessary: Acceleration due to gravity, g = 9.8ms 2 Speed of light in a vacuum, c = 3.0 10 8 ms 1 Electron Charge, e = 1.6 10 19 C Electron mass = 9.11 10 31 kg Permeability of free space = 4.0 10 7 Hm 1 Permittivity of free space, o = 8.85 10 12 Fm 1 The constant 1 4 o ©[email protected] GHS-Never Give Up1 = 9.0 10 9 F 1 M SECTION A 1.(a) Distinguish between real and virtual images. (2) (b) Show that an image formed by a plane mirror is as far behind the mirror as the object is in front. (4) (c) Explain with the aid of a diagram how you can determine the focal length of a convex mirror using a convex lens. (5) (d) A concave mirror forms a real image which is three times the linear size of a real object. When the object is displaced through a distance 𝑑,the real image formed is now four times the linear size of the object. If the distance between the two image positions is 20.0cm,find (i) the focal length of the mirror. (3) (ii) the distance d. (3) (e) Explain how a mirage is formed. (3) 2.(a) Define refractive index of a medium. (1) 1 1 1 (b) Derive the formula for two thin lenses in contact by f1 f 2 f considering a point object O placed on their principal axis. (4) (c ) Describe an experiment to determine the refractive index of a small quantity of liquid using a plane mirror and a convex lens. (5) (d)(i) What is chromatic aberration. (1) (ii) Write down the expression for the focal length f of a lens in terms of n the refractive index of glass in which the lens is made, r1 , r2 are the radii of curvature of the lens surfaces. (1) (ii) The refractive index of crown glass for blue light is 1.523,while that for red light is 1.513,suppose the radii of curvature of the surfaces of the lens are 15cm and 12cm,find the separation of the foci for red and blue light. (2) (e)(i) Draw the diagram of a Galilean telescope with final image at near point. (3) (ii) With the aid of a diagram derive the expression for the angular magnification of the telescope in e (i) above. ©[email protected] GHS-Never Give Up2 (3) SECTION B (WAVES) 3.(a) Explain what is meant by (i) (ii) (iii) wavefront the principle of superposition of waves. doppler effect (1) (2) (2) (b) Use the principle of superposition of waves to explain the formation of (i) (ii) stationary waves. beats (c ) Derive an expression for the frequency of sound waves received by an observer in terms of the frequency of the sound, the speed of the source of the sound waves ,and the speed of the sound, (i) when the source is approaching the observer. (ii) when the source and the observer are both moving towards each other. (3) (d) A stationary observer notices the pitch of a siren of a police car change in the ratio of 4:3 on passing him. If the speed of sound is 350ms-1,calculate the speed of the car. (5) (2) (2) 4.(a) What is meant by interference of light waves? (b) State the conditions necessary for the observation of interference pattern. (3) (1) (2) (c ) Two coherent sources a distance 𝑎 apart produce light of wavelength,𝜆,which overlap at a point on a screen a distance,D,from the sources to form an interference pattern. (i) Show that the fringe width 𝑦 is given by 𝑦 = (ii) In Young’s double slit experiment the 8th bright fringe is formed 5mm away from the centre of the fringe system when the wavelength of light used is 6.2 × 10−7 𝑚.Calculate the separation of the two slits if the distance from slits to the screen is 80cm. (3) ©[email protected] GHS-Never Give Up3 𝜆𝐷 𝑎 (6) (ii) State one advantage of using Fresnel’s biprism over Young’s double slit experiment in determining in obtaining an interference pattern. (1) (d) State one application of interference. (e) Explain with the aid of diagrams what you understand by the terms Division of wavefront (3) Division of amplitude. (3) (i) (ii) (1) SECTION C (MAGNETISM) 5.(a)Define (i) the Tesla (1) (ii) magnetic moment of a coil. (1) (b)(i) Write the expression for the force on a charge of Q coulombs moving with a velocity v ms 1 at an angle to a uniform magnetic field of flux density B tesla. (1) (ii) Use the expression in b(i) above to deduce the force on a conductor carrying current in a magnetic field. (3) (iii) A straight horizontal conducting rod of length 0.45m and mass 60g is suspended by two vertical wires at its ends. A current of 5A is set up in the rod through the wires. What magnetic field should be set up normal to the conductor in order that the tension in the wires is zero? (4) (c) A rectangular coil of N turns and area Am 2 is suspended in a uniform magnetic field of flux density B tesla. Initially the plane of the coil is at right angles to the magnetic field. Derive the expression for the initial couple on the coil when a current I amperes flows through the coil. (5) (d ) A small circular coil of 10 turns and mean radius 2.5cm is mounted at the centre of a long solenoid of 750 turns per metre with its axis at right angles to the axis of the solenoid. If the current in the solenoid is 2.0A, calculate (i) the magnetic flux density inside the solenoid. (ii) the initial torque on the circular coil when a current of 1.0A is passed through it. (2) ©[email protected] GHS-Never Give Up4 (3) 6.(a)(i)State the laws of electromagnetic induction. (2) (ii) State the factors upon which the magnitude of emf induced in a conductor depends, if the conductor is situated in a changing magnetic field. (2) (iii) Describe an experiment to demonstrate each of the laws in a(i) above. (7) (b) An aeroplane has a wing span of 20m.The plane is flying on a straight horizontal North –south course at a speed of 200ms 1 .If at some point of the plane’s course the magnetic flux density is 5.0 10 5 T and the angle of dip is 70 0 ,calculate the emf induced between the tips of the plane’s wings. (5) (c) A copper ring is suspended by a thread in a vertical plane. One end of a magnet is brought horizontally towards the ring as shown in the figure below. Thread. Copper ring N (i) (ii) S What observation is made? Explain the observation in c(i) above. (1) (3) 7. (a) (i)Distinguish between root mean square value and peak value of an alternating current. (2) (ii) What is the peak value of the voltage from a 240 a.c mains? (2) (b) Describe with the aid of a labelled diagram the structure and action of a hot wire instrument. (5) (c)(i) What is meant by the term inductive reactance? (ii) (1) Derive the expression for the reactance of an inductor of inductance L when a sinusiodally varying alternating current of frequency f ,passes through it. (5). ©[email protected] GHS-Never Give Up5 (iii) (d) A 50mH inductor is connected to a 220V,50Hz ac supply. Determine the r.m.s value of current in the circuit. (3) State two advantages of a.c over d.c (2) SECTION D (ELECTRICITY) 8.(a) Define electric field intensity. (1) (b)(i) Find the electric field intensity at point P in the diagram below given that a 5C charge is placed at A and a 3.6C is placed at B and that the charges are situated in a vacuum. (5) 5C A 8cm 3.6C B 10cm 6cm P (ii) The bob of a pendulum of mass 80mg and having a charge of 2 10 8 C is swinging in a uniform horizontal electric field of 2 10 4 V / m. Find the tension in the string of the pendulum and the angle made by it with the vertical. (4) (c) A and B are plates of a charged capacitor ,M is a metal ball placed between them. Draw the lines of force in the region between the plates. + M (d) (i) Derive the expression relating electric potential and electric field intensity. (2) (3) (ii) Explain why the electric field intensity close to the surface of a charged conductor is always at right angles to the surface of the conductor. (2) (e) A positively charged metal sphere P is placed adjacent to a neutral conductor R as shown in figure below. ©[email protected] GHS-Never Give Up6 P R + Sketch the graph to show how the electric field intensity varies with distance from the left of P to a point on the right of R. (3) 9.(a) (b)(i) Define the terms electromotive force and internal resistance. (2) With the aid of a labelled diagram describe how a slide wire potentiometer can be used to measure low voltages of the order of milli volts. (5) (ii) Explain the reasons why a Wheatstone bridge circuit is not suitable for comparison of resistances which are either very low or very high. (2) (c) A dry cell gives a balance length of 84.8cm on a potentiometer wire. When a resistor of resistance 15Ω is connected across the terminals of the cell ,a balance length of 75.0cm is obtained. Find the internal resistance of the cell. (3) (d ) X 994Ω A 996Ω D B 2 S 1 G (i) In the circuit above ,X, is an accumulator of negligible internal resistance. AB is a uniform wire of resistance 10Ω.G is a galvanometer connected to a sliding contact D. When switch S is thrown to position 1, G shows no deflection when AD is 60.0cm,when S is thrown to position 2 ,G shows no deflection when AD is 40.0cm. Find the e.m.f of the thermocouple. (3) (ii) e.m.f of cell X. ©[email protected] GHS-Never Give Up7 (3) (d) State two advantages of a potentiometer over a voltmeter in the measurement of voltage. (2) 10.(a) Sketch field lines between two large parallel metal plates across which a p.d is applied. (1) (b) Describe how you would investigate the factors which affect the capacitance of a parallel plate capacitor using a gold leaf electroscope. (6) ( c)(i) Explain why a charged spherical conductor loses charge faster when a pin is attached to it. (3) (d) (e) A charged oil-drop of radius 1.3 10 6 m is prevented from falling under gravity by the vertical field between two horizontal plates charged to a difference of potential of 8340V.The distance between the plates is 16mm,and the density of oil is 920kgm-3.Calculate the magnitude of the charge on the drop. (4) Describe with the aid of a diagram, how a high voltage can be generated using a Van de Graaf generator. (6) ©[email protected] GHS-Never Give Up8