2013 JJC H2 Physics P2

JJC 2013 9646/Prelims P2/2013 [Turn Over JURONG JUNIOR COLLEGE 2013 Preliminary Examination Name Class 12S PHYSICS Higher 2 Structured Questions Candidates answer on the Question Paper. No additional materials are required. 9646/2 4 Sep 2013 1 hour 45 minutes READ THESE INSTRUCTIONS FIRST Do not open this booklet until you are told to do so. Write your name and class in the space provided at the top of this page. Write in dark blue or black pen. You may use a soft pencil for any diagrams, graphs or rough working. Do not use highlighters, glue or correction fluid. There are eight questions in this paper. Answer all questions. At the end of the examination, fasten all your work securely together. The number of marks is given in brackets [ ] at the end of each question or part question. For Examiner’s Use 1 /5 2 /6 3 /10 4 /7 5 /10 6 /8 7 /14 8 /12 Total /72 (This question paper consists of 20 printed pages)

JJC 2013 9646/Prelims P2/2013 [Turn Over 2 Data speed of light in free space, c = 3.00  108 m s1 permeability of free space, o = 4  107 H m1 permittivity of free space, o = 8.85  1012 F m1 = (1/(36))  109 F m1 elementary charge, e = 1.60  1019 C the Planck constant, h = 6.63  1034 J s unified atomic mass constant, u = 1.66  1027 kg rest mass of electron, me = 9.11  1031 kg rest mass of proton, mp = 1.67  1027 kg molar gas constant, R = 8.31 J K1 mol1 the Avogadro constant, NA = 6.02  1023 mol1 the Boltzmann constant, k = 1.38  1023 J K1 gravitational constant, G = 6.67  1011 N m2 kg2 acceleration of free fall, g = 9.81 m s2 Formulae uniformly accelerated motion, s = ut + 1 2 at2 v2 = u2 + 2as work done on/by a gas, W = p V hydrostatic pressure, p = gh gravitational potential,  =  Gm r displacement of particle in s.h.m., x = xo sin t velocity of particle in s.h.m., v = vo cos t v = 22() ox x mean kinetic energy of a molecule of an ideal gas E = 3 2 kT resistors in series, R = R1 + R2 + . . . resistors in parallel, 1/R = 1/R1 + 1/R2 + . . . electric potential, V = o Q ε r4 alternating current / voltage, x = xo sin t transmission coefficient, T  exp(2kd) where k = 2 2 8( )mU E h  radioactive decay x = xo exp(-λt) decay constant λ = 1/ 2 0.693 t

JJC 2013 9646/Prelims P2/2013 [Turn Over 3 1 The period of oscillation of a pendulum is given by the equation 2 lT g where l is the length of the pendulum and g is acceleration of free fall. To determine g, a student obtained the following data: Period of oscillation = (0.910  0.005) s Length of pendulum = (20.6  0.1) cm (a) Determine the percentage uncertainty in g. percentage uncertainty = % [2] (b) Express g together with its associated uncertainty. g = (  ) m s-2 [3]

JJC 2013 9646/Prelims P2/2013 [Turn Over 4 2 A person supports a load of 20 N in his hand as shown in Fig 2.1. The system of the hand and load is represented by Fig 2.2. The rod represents the forearm and T represents the tension exerted in the biceps. The forearm weighs 60 N. (a) Show that the tension T in the biceps is 433 N. [2] (b) Determine the magnitude and direction of the force acting at the elbow. Fig. 2.1 Fig. 2.2 Elbow Forearm Rod

JJC 2013 9646/Prelims P2/2013 [Turn Over 5 magnitude of force = N [3] direction of force = [1] 3 (a) In one type of C.R.O., the electrostatic def lection system consists of two parallel metal plates with a separation of 0.50 cm, as shown in Fig. 3.1. Fig. 3.1 The centre of the plates is situated 15 cm from a screen. A potential difference of 80 V between the plates provides a uniform electric field in the region between the plates. Electrons of speed 3.1 x 10 7 m s-1 enter this region at right angles to the field. The electron takes a time of 6.5 x 10-10 s to pass between the plates. Calculate (i) the force on an electron due to the electric field, force = N [2] (ii) the acceleration of the electron along the direction of the electric field, acceleration = m s -2 [1] c.r.o. screen 15 cm electrons 3.1 x 107 m s-1 - + 0.50 cm

JJC 2013 9646/Prelims P2/2013 [Turn Over 6 (iii) the speed of the electron at right angles to its original direction of motion as it leaves the region between the plates. speed = m s -1 [2] (b) Hence, by considering your answer to (a)(iii) and the original speed of the electron, estimate the deflection of the electron beam on the screen. deflection = cm [2] (c) (i) Figure 3.2 represents the front of the screen of the c.r.o. Fig. 3.2 Mark on Fig. 3.2 the position of the deflected beam of electrons. Label your answer A. [1] 1 cm 1 cm undeflected beam

JJC 2013 9646/Prelims P2/2013 [Turn Over 7 (ii) On Fig. 3.2, draw a sketch diagram to show the trace on the screen if the p.d. across the plates varies sinusoidally with r.m.s. value 80 V. Label your sketch S. [2] 4 (a) Define the tesla. [1] (b) Two wires X and Y, which are at right angles to the plane of the paper, carry currents Ix, and Iy out of the plane of paper and are separated by a distance r as shown in Fig. 4.1. The magnitude of Iy is twice the magnitude of Ix. (i) Sketch the pattern of magnetic field due to these wires on Fig. 4.2. [2] Y r X Ix Iy Fig. 4.1 Y X Fig. 4.2

JJC 2013 9646/Prelims P2/2013 [Turn Over 8 (ii) B, the magnetic flux density due to a long straight wire, is given by the expression oμB= 2πr I where permeability of free space, µo is 4 x 10-7 H m-1. In terms of Ix, Iy, r and µo, 1. write an expression for the magnetic flux density of wire X at wire Y, [1] 2. hence derive an expression for the force per unit length on wire Y. [1] (iii) One particular overhead powerline consists of 2 parallel cables with a separation of 5.0 m. The current in the first and second cable is 100 A and 200 A respectively. Explain why it is not possible, by looking at the cables, to detect the instant at which the current is switched on. [2] 5 (a) A scanning tunnelling microscope (STM) is able to map out atomic-scale images of surfaces by using the “tunnelling” effect of electrons across an energy barrier. (i) State what constitutes the energy barrier when using the STM. [1]

JJC 2013 9646/Prelims P2/2013 [Turn Over 9 (ii) Hence, describe briefly how the STM is able to map out atomic-scale images of surfaces. [2] (b) Distinguish between conduction band and valence band. [2] (c) A junction is formed between slices of p-type and of n-type semiconductor material, as shown in Fig 5. Fig. 5 (i) Describe the origin of the depletion region at the junction. [4] p-type material n-type material

JJC 2013 9646/Prelims P2/2013 [Turn Over 10 (ii) On Fig. 5, draw the symbol for a battery, connected so as to increase the width of the depletion region. [1] 6 (a) Explain what is meant by half-life. [1] (b) The thickness of a sheet of aluminium foil is to be monitored using β-radiation as illustrated in Fig. 6. Fig. 6 The separation of the rollers is controlled by the output from the detector with the intention of maintaining a constant foil thickness. (i) State and explain what would happen to the separation of the rollers if the output from the detector were to decrease.