2012 H2 P2 Prelim (for Other Jcs)

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NANYANG JUNIOR COLLEGEJC 2 PRELIMINARY EXAMINATIONHigher 2

CANDIDATENAME

CLASSTUTORSNAME

PHYSICS 9646/02Paper 2 Structured Questions 12 September 2012

1 hour 45 minutes

Candidates answer on the Question Paper.

No Additional Materials are required

READ THESE INSTRUCTIONS FIRST

Write your name and class on all the work you hand in.Write in dark blue or black pen on both sides of the paper.You may use a soft pencil for any diagrams, graphs or rough working.Do not use staples, paper clips, highlighters, glue or correction fluid.

Section AAnswer all questions.It is recommended that you spend about 1 hour 15 minutes on this section.

Section BAnswer Question 7.

It is recommended that you spend about 30 minutes on this section.

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 partquestion.

For Examiners Use

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Total

This document consists of 17 printed pages.

[Turn over


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NYJC 9646/02/PRELIM/2012

2

Data

Formulae

uniformly accelerated motion, s = ut +at2

v2 = u2 +2as

work done on/by a gas, W = pV

hydrostatic pressure, p = gh

gravitational potential, = /Gm r

displacement of particle in s.h.m. x = xosint

velocity of particle in s.h.m. v = vo cos t

= ( )22 xxo mean kinetic energy of a moleculeof an ideal gas

E =3

2kT

resistors in series, R = R1 + R2 +

resistors in parallel, 1/R = 1/R1 +1/R2 +

electric potential, V = Q/ 4or

alternating current/voltage, x = xosint

transmission coefficient, T = exp(-2kd)

where k = (((( ))))2

2

8 m U E

h

radioactive decay, x = xoexp (-t)

decay constant =

21

693.0

t

speed of light in free space, c = 3.00 x 108 m s-1

permeability of free space, o = 4 x 10-7 H m-1

permittivity of free space, o = 8.85 x 10-12 Fm-1

(1 / (36 )) x 10-9 Fm-1

elementary charge, e = 1.60 x 10-19 C

the Planck constant, h = 6.63 x 10-34 J s

unified atomic mass constant, u = 1.66 x 10-27 kg

rest mass of electron, me = 9.11 x 10-31 kg

rest mass of proton, mp = 1.67 x 10-27 kg

molar gas constant, R = 8.31 J K-1 mol-1

the Avogadro constant, NA = 6.02 x 1023 mol-1

the Boltzmann constant, k = 1.38 x 10-23 J K-1

gravitational constant, G = 6.67 x 10-11 N m2 kg-2

acceleration of free fall, g = 9.81 m s-2acceleration of free fall g = 9.81 m s-


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Section A

Answer all questions.It is recommended that you spend about 1 hour 15 minutes on this section.

1 A uniform ladder of weight Wrests against a rough vertical wall, and is tilted at an angle from the rough horizontal ground. Fig. 1 shows the free-body diagram of the ladder. NG is thenormal reaction force acting on the ladder due to the ground while NW is the normal reaction

force acting on the ladder due to the wall.

Fig. 1

(a) Complete Fig.1 by including the frictional forces fWand fG exerted by the wall and theground respectively. [1]

(b) By taking moments about an appropriate point, show that

tan2

W G

WN N=

[2]

(c) Given that W= 100 N, = 40, and NG= 70 N, determine the value of fG.

fG= N [2]

W

NG

NW

Wall

Ground


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(d) Some rubbery material is attached to the top of the ladder. State with explanations, ifany, how NGand NWwill change.

[2]

2 A piece of resistance wire PQ is connected to a cell of e.m.f. E1 of internal resistance r inseries with external resistor Ras shown in Fig. 2.1. The resistance of PQ is 1.2R.

Fig. 2.1

(a) Show that the potential difference across PQ is 11.2

2.2

RE

R r+.

[2]

(b) A potentiometer shown in Fig. 2.2 is set up to determine the internal resistance rof thecell E1 which is placed in series with a variable resistor R. A standard cell of e.m.f. E2ofnegligible internal resistance is used in the secondary circuit. The galvanometer readszero when the jockey is placed at J, such that PJ:JQ = 1:3.

Fig. 2.2

E1 r R

P Q

E1 r R

P QJ

E2


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(i) Given E1 = 12.0 V, E2 = 1.5 V and R = 2.0 , find the value of the internalresistance, r.

r= [3]

(ii) Determine the values for the current through E1 and E2when the jockey is at J.

current through E1= A

currentthrough E2= A [2]

(iii) While still in contact with the wire PQ, the jockey is shifted nearer to Q. Suggest apossible change so that the galvanometer reads zero again.

[1]

3 A space station orbits the Earth once every 200 minutes. Its orbit is 4900 km above thesurface of the Earth, which has a radius of 6400 km.

(a) Show that the acceleration of the space station is 3.1 m s-2.

[2]

(b) Hence determine the mass of the Earth.

mass of Earth= kg [2]


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(c) A crate of mass 5.2 kg is found inside the space station. Determine the magnitude anddirection of the resultant force acting on the crate.

magnitude of resultant force= N

direction of resultant force= [2]

(d) Explain why the crate in (c) can be said to experience weightlessness.

[1]

4 (a) Laser beams are described as being highly coherent. Explain what being coherentmeans, and the way in which a laser beam is coherent.

[2]

(b) Explain the meaning of the term population inversion.

[2]

(c) Describe how population inversion facilitates the formation of a coherent laser beam.

[2]


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Fig. 5.1

T

C

adjustment

spring balance

D

SN N

5 A loudspeaker magnet NSN has its movingcoil C attached to a spring balance, asshown in Fig. 5.1. (The paper cone,normally attached to the cardboard cylinderforming the coil, is not shown.)

Current was passed through the coil C, andthe spring balance support T was adjusted

so that the coil C was restored to its originalposition. The readings F on the balance(which has a certain zero error present) forvarious current I were plotted in Fig. 5.2.

(a) Draw the best fit line and determine the gradient of the line.

gradient = N A-1 [3]

Fig. 5.2

F / N vs/ A3.50

3.00

2.50

2.00

1.50

1.000.100 0.200 0.300 0.400 0.500 0.600 0.700 0.800 0.900


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(b) Determine the zero error of the balance.

zero error = N [2]

(c) If the mean diameter, D, of the coil is 0.025 m and the number of turns is 50, calculatethe flux density at the coil, assuming that the field is radial.

flux density = T [3]

6 (a) An experiment was performed to investigate photoelectric effect. Fig. 6.1 shows theresult for one value of wavelength.

0

1

2

3

4

5

6

0 1 2 3 4 5 6

Fig. 6.1

(i) Give one observation of photoelectric effect that provides evidence for theparticulate nature of electromagnetic radiation.

[1]

Workfunction

/ eV

Stopping potential Vs/ V


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(ii) Explain how the observation stated in (a)(i) illustrates the particulate nature ofelectromagnetic radiation.

[1]

(iii) Mark on Fig. 6.1 the result of shining light of wavelength 1.55 10 -7 m on thesame material. [1]

(b) Fig. 6.2 shows a filament bulb emitting white light surrounded by a region of cooler

helium gas.

State and explain the type of helium spectrum observed from

(i) point B

[2]

(ii) point A

[1]

B

A

bulb emitting

white light

coolerhelium gas

Fig. 6.2


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(c) An interesting quantum mechanical effect occurs in alpha decay. Fig. 6.3 shows how

the potential energy of an -particle inside a nucleus varies with distance and thedotted line gives the total energy of an -particle. R0 is the radius of the nucleus.

Classically, it is impossible for an -particle to escape.

Explain how alpha decay occurs.

[3]

Potentialenergy U

Fig. 6.3

Total energy

of -particle

R0distance


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7 The diagram below shows a gamma ray detector receiving gamma radiation from aradioactive source. S is the number of gamma photons emitted per unit time. The detectorwill only detect a fraction of this number. Nis the number of gamma photons detected by thedetector per unit time.

Unless otherwise stated, background count has already been corrected for.

(a) Suggest two reasons why the quantity Sis not equal to N.

[2]

The efficiency of the detector, is defined as N / S.

Table 7.1 shows how varies with the energy of the gamma photons, E.

(b) Complete the first four columns in Tables 7.1. [2]

Energy of GammaPhoton, E/ keV

S/ s-1 N/ s-1 Efficiency,

60 2000000 42400 0.0212

86 1850000 69005 0.0373

123 1589000 0.0330

345 1480000 35520

769 11978 0.0186

962 820000 14186 0.0173

1406 1170000 0.0153

Table 7.1

It is suggested by a scientist that energy of Gamma photon is related to the efficiencyaccording to the equation shown below up till the lower limit of 80 keV.

BAE=

where A and Bare constants.

RadioactiveSource

Entry Window

for photons

Body ofDetector


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(c) Plot a suitable graph on the grid provided below for a range of86 keV 1406 keVE to determine the value of A and B in SI units where

applicable. Quote all values to 3 significant figures. (You may use the two extracolumns on the right of Table 7.1 to tabulate other quantities.)

A =

B= [4]


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(d) There is a general trend of an increase in the efficiency with decreasing Gamma rayenergy. However, when the energy of the gamma ray is 60 keV, the efficiency dropssuddenly. Suggest two possible reasons for this.

[2]

(e) This detector is now used to study the activity of an unknown Gamma ray source. Theaverage energy of each gamma photon is 200 keV. The detector registered a totalcount of 26157600 in a time interval of 10 minutes. Calculate the activity detected bythe detector, N.

N= Bq [2]

(f) Calculate the actual activity, S, of the source.

S= Bq [2]

(h) Suggest one possible problem when using this detector to study the activity of aradioactive source that emits 1 MeV gamma photons. The radioactive sample isuniform and has a half-life of 10 minutes.

[1]


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Section B

It is recommended that you spend about 30 minutes on this section.

8 Beta particles can be deflected by magnetic fields.

Design a laboratory experiment to investigate how magnetic flux density affects the anglethrough which beta particles are deflected when they pass through a uniform magnetic field.

The only radioactive source that is available to you is a Radium-226 source which emits , and radiation.

You should draw a diagram showing the arrangement of your apparatus. In your account youshould pay particular attention to

(a) the procedure to be followed

(b) the method by which beta particles only would be detected

(c) the method of measuring angle of deflection

(d) how the magnetic field would be produced, measured and changed

(e) any safety precautions you would take.

[12]


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Diagram


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2012 H2 P2 Prelim (for Other Jcs)