GCSE Additional Applied Science June 2008 Communications Paper B

GENERAL CERTIFICATE OF SECONDARY EDUCATION A326/02 TWENTY FIRST CENTURY SCIENCE ADDITIONAL APPLIED SCIENCE A Communications (Higher Tier) FRIDAY 20 JUNE 2008 Morning Time: 45 minutes Candidates answer on the question paper. Additional materials (enclosed): None Calculators may be used. Additional materials: Pencil Ruler (cm/mm) H * C U P /T 4 3 7 7 5 * This document consists of 11 printed pages and 1 blank page. SP (SJF4643/TC) T43775/5 © OCR 2008 [A/103/3783] OCR is an exempt Charity [Turn over INSTRUCTIONS TO CANDIDATES • Write your name in capital letters, your Centre Number and Candidate Number in the boxes above. • Use blue or black ink. Pencil may be used for graphs and diagrams only. • Read each question carefully and make sure that you know what you have to do before starting your answer. • Answer all the questions. • Do not write in the bar codes. • Write your answer to each question in the space provided. INFORMATION FOR CANDIDATES • The number of marks for each question is given in brackets [ ] at the end of each question or part question. • The total number of marks for this paper is 36. FOR EXAMINER’S USE Qu. Max Mark 1 6 2 7 3 5 4 8 5 5 6 5 TOTAL 362 © OCR 2008 Answer all the questions. 1 John is a disc jockey. (a) He likes to play old music recorded on vinyl discs. The old music is recorded on the disc as an analogue signal. He knows that music sometimes sounds better when it is recorded as a digital signal. (i) Here are four oscilloscope traces of signals. AC BD Which one is a digital signal? answer .......................................................... [1] (ii) Why might music sound better when it is recorded as a digital signal? .......................................................................................................................................... ..................................................................................................................................... [1]3 [Turn over © OCR 2008 (iii) Suggest another advantage of recording music as a digital signal. .......................................................................................................................................... ..................................................................................................................................... [1] (b) John decides to transfer part of his favourite vinyl recording to the hard disc of his computer. The analogue recording is converted into a digital signal. This is stored as a file in the computer. Here is some information about the conversion process. digital sample 12 bits sample rate 42 000 samples per second length of recording 15 seconds (i) Show that 504 000 bits are needed to store each second of the recording. [1] (ii) How many bits are needed to store 15 seconds of the recording? answer .................................................. bits [1] (iii) How would you convert this file size from bits into bytes? .......................................................................................................................................... ..................................................................................................................................... [1] [Total: 6]4 © OCR 2008 2 Sue uses an oscilloscope to test a radio transmitter. © OCR (a) Here is one of the signals that she observes. 2 V 0.005 s Use the information to calculate: (i) the amplitude of the signal. amplitude = ..................................................... V [1] (ii) the frequency of the signal. frequency = ................................................... Hz [2]5 [Turn over © OCR 2008 (b) Here is a block diagram for the radio transmitter. microphone oscillator modulator amplifier aerial (i) Describe the function of the amplifier. .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [2] (ii) Describe the function of the aerial. .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [2] [Total: 7]6 © OCR 2008 3 The circuit diagram shows an integrated circuit powered by a 6V battery. integrated circuit 80 Ω 6V (a) The switch is closed to power the integrated circuit. The voltage across the LED is 2V. (i) Explain why the voltage across the resistor is 4V. .......................................................................................................................................... ..................................................................................................................................... [1] (ii) Calculate the current in the 80Ω resistor. Use I = VR . current = ..................................................... A [2] (b) The switch needs a current rating of 1A. Suggest why this needs to be much greater than the current in the LED. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. ............................................................................................................................................. [2] [Total: 5]7 [Turn over © OCR 2008 4 One fax machine sends a copy of a document to another fax machine. An optical fibre links the two machines. optical fibre link first fax machine second fax machine (a) Complete this block diagram for the system. encoder decoder processor input processor link output [3] (b) Describe the function of the input block and encoder. Include the form of the signal passed onto the link. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. ............................................................................................................................................. [3] (c) The link between the fax machines could be made with copper wires instead of optical fibre. This would cost less. Suggest advantages of using optical fibre instead of copper wire for the link. .................................................................................................................................................. .................................................................................................................................................. ............................................................................................................................................. [2] [Total: 8]8 © OCR 2008 5 Matt gets some money from a cash machine. (a) He presses buttons on a keyboard to enter his security number. The number is sent across the internet to his bank. (i) Explain why the number is encrypted before it enters the internet. .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [2] (ii) The number can only be encrypted if it is in digital form. This also means that it can be compressed. Explain the advantages of compressing digital information. .......................................................................................................................................... .......................................................................................................................................... ..................................................................................................................................... [2] (b) The cash machine uses programmable electronic systems. Why does this reduce the cost of the machine? .................................................................................................................................................. ............................................................................................................................................. [1] [Total: 5]9 [Turn over © OCR 2008 6 Live outside broadcasts allow people all over the world to watch a sporting event. (a) Here is an incomplete block diagram for a live outside TV broadcast system. editing suite receiver Complete the block diagram. Use words from this list. cameras microphones transmitter satellite [2] (b) The system is managed by the people in the editing suite. Describe what these people do to produce the broadcast. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. .................................................................................................................................................. ............................................................................................................................................. [2]10 © OCR 2008 (c) The receiver contains an aerial. What is the best type of aerial for the receiver? Put a ring around the correct answer. dish dipole rod wireless [1] [Total: 5] END OF QUESTION PAPER11 © OCR 2008 BLANK PAGE PLEASE DO NOT WRITE ON THIS PAGE12 © OCR 2008 PLEASE DO NOT WRITE ON THIS PAGE Permission to reproduce items where third-party owned material protected by copyright is included has been sought and cleared where possible. Every reasonable effort has been made by the publisher (OCR) to trace copyright holders, but if any items requiring clearance have unwittingly been included, the publisher will be pleased to make amends at the earliest possible opportunity. OCR is part of the Cambridge Assessment Group. Cambridge Assessment is the brand name of University of Cambridge Local Examinations Syndicate (UCLES), which is itself a department of the University of Cambridge.