Level 3 Science, 2006

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Level 3 Science, 2006

90732 Describe selected properties and applications of

EMR, radioactive decay, sound and ultrasound

9 0 7 3 2

For Supervisor’s use only

3

Credits: Four

9.30 am Tuesday 28 November 2006

Check that the National Student Number (NSN) on your admission slip is the same as the number at the top of this page.

You should answer ALL the questions in this booklet.

If you need more space for any answer, use the page(s) provided at the back of this booklet and clearly number the question.

Check that this booklet has pages 2–11 in the correct order and that none of these pages is blank. YOU MUST HAND THIS BOOKLET TO THE SUPERVISOR AT THE END OF THE EXAMINATION.

For Assessor’s

use only Achievement Criteria

Achievement Achievement _{with Merit} _{with Excellence}Achievement

Describe selected properties and applications of EMR, radioactive decay, sound and ultrasound.

Explain selected properties and applications of EMR, radioactive decay, sound and ultrasound.

Discuss selected properties and applications of EMR, radioactive decay, sound and ultrasound.

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You are advised to spend 45 minutes answering the questions in this booklet.

QUESTION ONE: RADIOACTIVE DECAY

Radioactive isotopes that emit gamma rays are regularly used in medical diagnosis. One of the common radioactive isotopes used in medical imaging is technetium-99m.

Technetium-99m (Tc-99m) is an unstable form of technetium-99 (Tc-99). Tc-99m is generated by hospitals from molybdenum-99 (Mo-99) as it is needed.

(a) Complete the equation below for the decay of molybdenum-99 to form technetium-99m

Mo

42 99

+ Tc

43m

99

(b) How many protons and neutrons are contained in the nucleus of one Tc-99m atom? Number of neutrons

Number of protons

Tc-99m forms Tc-99 by emission of gamma radiation. Tc-99m emits gamma radiation with a half-life of 6 hours.

(c) After a patient is injected with a sample of Tc-99m, a Geiger counter initially records

12 400 counts per second.

Calculate the expected count rate from the patient 24 hours later.

Assessor’s use only

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(d) Technetium exists in a number of isotopes other than Tc-99. Describe what is meant by the term isotope.

(e) Discuss why radioisotopes with short half-lives (like Tc-99m at 6 hours) are used for medical

diagnosis.

Include both advantages and disadvantages in your answer.

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QUESTION TWO: ELECTROMAgNETIC RADIATION

Part of an advertisement showing an out-of-date method to fit shoes.

Adapted from: http://www.orau.org/ptp/collection/shoefittingfluor/shoe.htm

During the 1930s, 1940s and 1950s, simple X-ray machines were found in some shoe shops. Customers put their foot in the shoe and then into the machine. X-rays passed through the foot and made an image of the foot and the outline of the shoe on a screen. The image on the screen could be viewed through an eyepiece and showed if the shoe was a correct fit.

(a) Explain how the properties of X-rays allow an image of the foot and shoe to be formed.

For copyright reasons, this resource

cannot be reproduced here.

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Science 90732, 2006

(b) Explain why these machines are not used in shoe shops now.

(c) An X-ray machine emits X-rays with a period of 1.3 × 10–18 _s.

(i) Calculate the frequency of the X-rays.

(ii) Calculate the wavelength of the X-rays. The speed of light is 3.0 × 108_{m s}–1_.

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QUESTION THREE: ECLIPSES AND SHADOWS

Total solar eclipses are observed somewhere in the world nearly every year. Below is a diagram of a solar eclipse.

SUN

MOON EARTH

Shadow 2 Shadow 1

(a) (i) Name the TwO types of shadow shown on the diagram above. Shadow 1

Shadow 2

(ii) Describe the property of light that causes an eclipse to be formed.

(b) Explain why there are two types of shadow produced in an eclipse.

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(c) On the diagram below, show the shadow produced when the source of light is very tiny. Label your diagram.

Dot shows size of light source. Object Screen 7 Assessor’s use only

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QUESTION FOUR: SOUND AND ULTRASOUND

(a) while standing inside an empty concert hall with smooth hard walls, a science student notices that the sound of a single clap takes several seconds to die away.

Discuss why the sound takes several seconds to die away.

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(b) The diagram below is a side view of a concert hall showing some of the features which enable the sound to be projected to the different seating areas in the auditorium.

member of audience upper seating (Dress Circle) middle seating (Circle) Reflector 2 Reflector 1 Performer lower seating (Stalls)

Roof

Modified from UB Science Paper, 1995, page 11

(i) Explain which seating area of the concert hall Reflector 2 is designed to reflect sound into. Draw the path taken by sound waves onto the diagram above to assist your answer.

(ii) A member of the audience is seated 40 m in a direct line from the performer. The speed of sound through is 330 m s–1_{. Calculate how long the sound takes to travel directly}

through the air from the performer to the audience member. Show all working.

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(c) A recording booth is built beside the concert hall. The walls of the recording booth have been designed to make them as sound-proof as possible. The diagram below shows the structure of the recording booth’s walls.

Wall (view from above)

stud _{acoustic insulation}

wall lining

stud

Discuss why the wall structures help to keep the recording booth sound-proofed. Refer to the properties of sound waves in your answer.

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Question number

Extra paper for continuation of answers if required. Clearly number the question.

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