Level 3 Science, 2008

Transcription

1 For Supervisor s Level 3 Science, Describe selected properties and applications of EMR, radioactive decay, sound and ultrasound Credits: Four 2.00 pm Thursday 20 November 2008 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 12 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 Achievement Describe selected properties and applications of EMR, radioactive decay, sound and ultrasound. Achievement Criteria Achievement with Merit Explain selected properties and applications of EMR, radioactive decay, sound and ultrasound. Overall Level of Performance Achievement with Excellence Discuss selected properties and applications of EMR, radioactive decay, sound and ultrasound. New Zealand Qualifications Authority, 2008 All rights reserved. No part of this publication may be reproduced by any means without the prior permission of the New Zealand Qualifications Authority.

2 2 You are advised to spend 45 minutes answering the questions in this booklet. QUESTION ONE : NUCLEAR DECAY (a) Complete this decay equation for the radioactive decay of caesium-137 (Cs-137) to barium-137 (Ba-137) Cs Ba + γ (b) Caesium exists in a number of different isotopes. Give the number of protons and neutrons in these two common caesium isotopes: Cs and Cs (c) Using the graph below, show that the half-life of Cs-137 is 34 years. 10 Decay of Cs Mass (g) Time (years)

3 (d) A sample of Cs-137 has an initial activity of MBq (MBq = mega becquerel). How long would it take for the activity of this sample to drop to MBq? Show your working. 3 (e) Alpha particles are a form of ionising radiation. Explain how alpha particles cause the formation of ions in the material they are moving through.

4 (f) One method of inspecting welded joints involves the use of radioactive decay. Welding is the process of attaching two pieces of metal together. A welder uses heat to melt the areas that are to be joined and then uses a molten filler material to help bond the metal pieces together. The radiation source is placed above the joint to be inspected and a film is placed below. The film when developed shows darker areas where it has been exposed to more radiation, as shown below. 4 For copyright reasons, this resource cannot be reproduced here. Adapted from One radiation source used is the radioisotope caesium -137 (Cs-137). By referring to the above diagram, discuss why gamma rays are more suitable for inspecting welds than alpha or beta particles.

5 5 QUESTION TWO : SOUND AND ULTRASOUND Long-tailed bats use echolocation by producing a series of ultrasonic pulses. These pulses reflect from objects and the echoes are detected when they return to the bats ears. The time taken for the echo to return to the bat indicates the distance from the object. The most common wavelength of ultrasound used by these bats is m. (a) Calculate the frequency, in Hertz, of the most common wave produced by these bats. The speed of sound in air is 330 m s 1.

6 (b) Sound travels as a longitudinal wave. Describe the movement of the particles in a longitudinal wave. A diagram may assist your answer. 6 (c) The floor of the cave is 20 m below the bat. How long would it take for the sound wave to return to the bat s ears once it has been produced? Give your answer to an appropriate number of significant figures. Give an appropriate unit with your answer.

7 7 Bats can use echolocation to identify the difference between solid objects and soft objects such as moths. The following graph shows the relative amplitude of the pulse sent by the bat. 1 Relative amplitude Time 1 (d) On the grids below sketch a graph showing the possible reflected waves (echoes) received by the same bat from: (i) the smooth floor of a cave Relative amplitude 1 Time 1 ` (ii) a moth. 1 Relative amplitude Time 1

8 (e) Discuss reasons for any changes the bat would observe in the echo from the moth if the moth was flying directly towards the bat. 8

9 QUESTION THREE : EMR X-rays are used to make images of luggage at airports to help identify potential weapons. (a) Explain how X-rays can be used to make images of the items within the luggage. Refer to the objects labelled in the diagram. 9 For copyright reasons, this resource cannot be reproduced here. previews/757/ jpg (b) The following diagram shows a typical electromagnetic radiation (EMR) wave. Relative amplitude 1 Time 1 Complete the diagram above by clearly labelling the : (i) (ii) amplitude of the wave wavelength of the wave. Question Three continues on the following page.

10 (c) One property of electromagnetic radiation is that it normally travels in straight lines. Shortwave radio waves are an example of electromagnetic radiation that can be used to transmit radio signals from one country to another. Discuss how short-wave radio waves transmitted in the UK can be heard as far away as the USA and also in China. A labelled diagram may assist your answer. 10 UK USA China

11 (d) 11 An aerial is built with a length equal to half of the wavelength of the radio wave it is trying to receive. One short-wave radio frequency commonly used is khz ( Hz). Given that radio waves travel at m s 1, calculate the length of the aerial that needs to be used to receive the signal broadcast at a frequency of khz. Give your answer to an appropriate number of significant figures and with an appropriate unit.

12 12 Extra paper for continuation of answers if required. Clearly number the question. Question number 90732