Elective

Geophysics (25 marks)

Question 28 -

(a)

Gravimetric surveys collect raw gravity data which must be further processedby the application of a number of corrections.The following data table, map, and cross-section are the result of a small-scalegravimetric survey. Station

Gravitational reading (raw data) (mgal)

A (datum station)

919158.r

B

97916r.6

C

979r74.2

Map of survey area

10 km

Cross-sectionof survey arca

3

a

100

o )a

E -5 0 d.

go u.]

Question 28 continues on page 3L

- 30-

Marks Question28 (continued)

Gravity data reduction involves the application of the following corrections: Application comment

Correction

Quantity

0.8 mgaUkm Subtract a correction for each

Latitude correction

kilometre south of datum Free air correction

0.3 mgaVm

Add a coffection for each elevation metre above sea-level

Bouguer correction

0.1 mgaUm

Subtract a correction for each metre abovethe datum station

The data for stationA, the datum station, has been processedas below: Correctionor calculation item

Station A (datum)

Latitude correction

-(0 x 0.8)

Free air correction

+(50x 0.3) - ( 0 x 0.1)

Bouguer correction

+15.0

Total correction Observedg at station

919158.r

Correctedg at station

979173.r

Correctedg at datum station

919rt3.r

Gravity anomaly at station (correctedg - correcteddatum g)

0

(i)

Outline the role of the Bouguer correction in the reduction of gravity data.

(ii)

Using a table format and the information provided, reduce the gravity data for stationsB and C, anddraw an inference about the geology of the survey data.

Question 28 continues on page 32

-3r-

4

Marks Question28 (continued)

(b)

(i)

During your study of geophysics you carried out a first-hand investigation to model the principles of reflection and refraction of seismicwaves. Describe how you ensured that the data obtained in your investigation were reliable.

(ii)

The diagram shows the parh of seismic wavesthrough Earth. Account for the curved path followed by all the waves, and justify why the S-type wave stops at the outer core and the p-type wave does not.

Crust Mantle

Key S = S-typewave P = P-type wave O = epicentre

Outer core Inner core

(c)

'Our understanding of Earth has changed as a result of developmentsin geophysics.' Discuss this statementwith reference to the geophysicalmethods you have studied.

Question28 continueson page33

- 32-

Question28 (continued)

(d)

(i)

The map below shows a pattern of magneticanomaliesrecordedin the rocks of the seabed.The stripesrepresentareasof positive and negative magneticanomaly.

135"

I25'

135"

125"

45"

Explain the formation of thesepaleomagneticpatterns.

Question 28 continues on page 34

Marks Question28 (continued)

(ii)

The spreadingrate of an ocean can be calculated using paleomagnetic data as shown. Use the information provided to calculate the spreading rate of the ocean,in units of mm/yr. 1.0

Age (Myr) 0 Normal

ffi

iiiiii:iiiiiiiiiri

Reversed

iiriiiiffi

'riiiiiiiii'iiii

Boundary

r.67

0.73 0.900.97 Magneticpolaritytime scale

AB(p tesla) 1.0

km from centre of ridge

-1 . 0 Magnetic anomaly profile acrossthe mid-oceanridge This diagram is to scale. mm 10 0

20

30

40

50

60

70

1 mm=1 km

End of Question28 - 34-

80

90

100

Marks

Question29 - Medical physics(25 marks) (a)

The acoustic impedance and density of a number of different types of body tissue,ultrasound gel and air are shown in the table: Acoustic impedance (kg.-2s-l x 106)

9.25x 102 1.00x 103 1.01x 103

(i) (ii)

Calculate the velocity of sound in fat tissue. ultrasound gel is usedto overcomethe excessivereflection from the skin during a scan.

2 3

Explain why this is necessary,justifying your response with calcurations.

(b)

During your study of Medical Physicsyou identified data sources,and gathered, processedand presentedinformation to explain why MRI scanscan be used to detect abnormalitiesin the body. (i)

(ii)

(c)

Describ-ethe criteria you would use to determine the reliability of a data sourcefor this purpose.

3

Explain why MRI scanscan be usedto detectcancerous tissues.

3

Advances in our understandingof the electromagnetic spectrum have allowed scientiststo investigatethe human body in more ietail. Assess the impact of these advances on the development of medical technologies.

Question29 continueson page36

- 35-

M

Question 29 (continued)

(d)

Bones can be v_iewedwith a range of different medical imaging techniques.The images shown below were obtained using three different techniques.

B (i)

C

The images shown above are an X-ray, a CAT scan and a bone scan (in no particular order). Identify the images labelled A, B and C.

(ii)

Compare the advantagesand disadvantagesof CAT scans to X-ray images.

(iii)

contrast the information provided by bone scanswith that obtained by CAT scansand X-ray images.

End of Question29

- 36-

Marks Question30 -Astrophysics (25 marks) (a)

(i)

Describe the spectroscopicobservationsthat would determinewhether a particular star is really a binary star system.

(ii)

The graph representsthe variation in brightnessof a binary star system.

3

a a O n -o b li

14

2t 28 Time(days)

Given that the mass of the system is determined to be 6 x 1032kg, calculate the averagedistancebetween the starswithin the system.

(b)

During your study of Astrophysics you performed a first-hand investigationinto the spectraproduced by different objects under different conditions. (D

Explain how you determinedthat the data you obtained were reliable.

)

Explain how the absorption spectrum of a star is produced, and how it can be usedto determinethe star'scomposition.

4

Astronomers employ arange of instrumentsand techniquesto observecelestial objects.

7

(ii)

(c)

Assess the impact of technological advanceson our understandingof the cosmos.

Question30 continueson page38

i

-37 -

Marks Question30 (continued) (d)

(H-R) diagram depicts a possible life cycle path of a TheHertsPrung-Russell known star.

-1 0 104

-5 c)

tl

IO2 E

F .o

cA

h .h

o)

Itr

=+ 1

d.

ct) 'l

t0-2

+1 0

+1 5 0 25 000 -0.6

A 10000 0.0

G 5000 +0.6

M 3000 +2.0

spectraltYPe temperature(K) colourindex

(i)

Describe the reactions that occur in stars at the points marked A, B and C in its life cycle.

(ii)

A' Explain what type and mass of star is most likely to be formed at point

2

(iii)

compare the life cycle of a star that has a mass gteaterthan 10 solar masseswith the one depicted at point A'

2

End of Question30

-38-

I

Marks From Quanta to Quarks (25 marks)

Question 31I

(a)

The Bohr picture of the atom explains the energy of the photons emitted when an electron falls from an initial orbit n, to find an orbit of nt. (, t) The various energiesdepend upon the quantity | ; - -:- | and the values for this term are given in the table. 1"7 ", )

rableof values "(+

ni-'-t I

2

I

2 0.7500

values of n, andnrfromlto 6 Afor 6

4

5

0.8889

0.9375

0.9600

0.9722

0.1389

0.1875

0.2100

0.2222

0.0486

0.0711

0.0833

0.0225

0.0347

3

-J

4

0.0122

5 6

(b)

(i)

Identify the physical reason for about one-half of the table appearing blank.

(ii)

Calculate the energy of the photon emitted when an elecffon falls from ni= 4 to nr= J.

You have gathered, processed and analysed information related to the developmentof atomic theory. (i)

Describe how you ensured that the information you gathered was reliable.

2

(ii)

The atomic theory changed as a result of the contributions of both Heisenbergand Pauli.

4

Analyse how the work of both scientistsmodified the atomic theory at that time.

Question31 continueson page40

- 39 -

Marks Question31 (continued)

( c)

Australiahas a large supply of uranium which may be usedin fissionreactorsto createenergy.The equation describesthe relevant transmutationreaction:

7

zllu + 10"-+ tr*Jsu * ZZKI+ 3jn Analyse how the processdescribedin this equationhas been developedinto a technologywhich producesa sustainedand controlledamountof energy.

(d)

The cyclotron, invented rn 1932, accelerateschargedparticlesto a very high speed.The diagram showsthe basic designof a cyclotron.The Dees provide a strong magnetic field into the plane of the page. Dee

Path of charged particle

Charged particle source

Supply of high frequency alternating voltage

(i)

Explain the physicalprinciplesinvolved in the designof the cyclotron.

3

(ii)

Account for the use of the cyclotron (or other accelerator) in the developmentof our understandingof matter.

)

(iii)

Quarks are an important part of the StandardModel of Matter. The table showsthe six typesof quark and their charge(in units of e,the chargeon an electron). Quark

Up

Down

Charge

+4e

-Ie

J

J

Strange Charm

-Ie J

*?,

Bottom

Top

-I"

+?e

J

Identify the quark composition of the proton and the neutron.

End of Question 31 _40_

J

Marks Question 32 -

(a)

Lately, traffic control authoritiesin NSW have beenreplacingthe incandescent bulbs in traffic lights with arrays of light emitting diodes (LEDs). Describethe structureand operationof an LED.

,,

(ii)

Explain why LEDs are preferableto ordinary light bulbs when used in traffic lights.

3

(i)

During your study of the Age of Silicon you identified data sources,and gathered, processed and analysed information to outline the rapid developmentof electronics.

(i)

(b)

The Age of Silicon (25 marks)

Describe the criteria you would use to determinethe reliability of a data sourcefor this purpose. (ii)

Circuits containinglogic gatesare an integralpart of modernelectronics. An exampleof such a circuit is given below.

,2

s

Identify each gate labelled1^,-Rand€ and, using a truth table, determine the value of p when A = 0, B = | and C = L

(c)

ComputerdevelopmentssinceWorld War II (1945) have beencharacterisedby increasingperformanceat decreasingcost.This trend may or may not continue in the future. Assessthis statement.

Question32 continueson page42

-4r-

Mr Question32 (continued)

(d)

The resistanceof a thermistor as a function of temperatureis as shown.

t2 1l

10 \ 9

t'I I

8 g

n< C)

()

6

a (t) 0)

5 4

\: \ \

a J

2

\

1 0

-20

- ,;- j '..''''''.- ...

20

40

60

80

100

120

("C) Temperature (i)

Deduce the sign of the temperaturecoefficient of the thermistor.Explain vour answer.

Question32 continueson page43

- 42-

Marks Question32 (continued)

(ii)

A potential divider sensor circuit using this thermistor and a fixed resistoris built as shown.

12Y

A chamber temperatureof +20oC is required. On connecting a resistor, the sensoroutput voltage as a function of temperatureis measuredand plotted as below. Determine the approximate sensitivity of the potential divider sensorin the temperaturerange 6'C to 20"C.

I2 11 10 '/

9 C)

oo

I

8 l

*

/'

6 /

5 li a d.

v)

/

4

{

a J

2

/"

I

I 0

-20

20

40

60

("C) Temperature

Question32 continueson page44 - 43-

80

100

r20

Marks Question 32 (continued)

(iii)

The output of the potential divider sensor is to be converted to give a -10.0V signal at20"C. Design a suitable feedback amplifier to achieve this conversion. Base your circuit on an operational amplifier and assume a +15 V power supply. Show,using a fully labelled diagram, how your circuit should be connectedto the temperaturesensor.

End of paper

- 44O Board of StudiesNSW 2006

4