A-LEVEL Electronics. ELEC1 Introductory Electronics Mark scheme June Version V1: Final Mark Scheme

Transcription

1 A-LEVEL Electronics ELEC Introductory Electronics Mark scheme 40 June 05 Version V: Final Mark Scheme

2 Mark schemes are prepared by the Lead Assessment Writer and considered, together with the relevant questions, by a panel of subject teachers. This mark scheme includes any amendments made at the standardisation events which all associates participate in and is the scheme which was used by them in this examination. The standardisation process ensures that the mark scheme covers the students responses to questions and that every associate understands and applies it in the same correct way. As preparation for standardisation each associate analyses a number of students scripts. Alternative answers not already covered by the mark scheme are discussed and legislated for. If, after the standardisation process, associates encounter unusual answers which have not been raised they are required to refer these to the Lead Assessment Writer. It must be stressed that a mark scheme is a working document, in many cases further developed and expanded on the basis of students reactions to a particular paper. Assumptions about future mark schemes on the basis of one year s document should be avoided; whilst the guiding principles of assessment remain constant, details will change, depending on the content of a particular examination paper. Further copies of this mark scheme are available from aqa.org.uk Copyright 05 AQA and its licensors. All rights reserved. AQA retains the copyright on all its publications. However, registered schools/colleges for AQA are permitted to copy material from this booklet for their own internal use, with the following important exception: AQA cannot give permission to schools/colleges to photocopy any material that is acknowledged to a third party even for internal use within the centre.

3 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 Question Part Subpart Marking Guidance Mark Comments Temperature (a) sensor Adjustable voltage ref Comparator Logic gate Audio signal generator Audio amplifier Loud speaker 7 Light sensor unit (b) Each box or dotted combination to be worth mark each if in correct sequence Op-amp comparator OR audio signal generator OR light sensor unit Potentiometer adjustable voltage reference Power MOSFET audio amplifier of

4 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 A B a b c d e f g Display L mark for row L mark for row S (both) mark for row H (a) S S 0 0 H (b) EXOR gate (c) Common cathode display requires logic applied to segment as all cathodes are held low Two points made Common anode requires logic 0 to be applied to light each segment (d) (i) Different combinations produce different brightness Disadvantage (d) (ii) R=V/I; (5V.V) / 0mA;.8V/0mA = 40Ω mark for.8v drop mark for answer (d) (iii) E4 = 50Ω mark for answer 4 of

5 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 V R X S (a) PROJECT 0V Y mark for Zener symbol mark for orientation (b) (i) 80mA + 5mA = 85mA Answer (b) (ii) V 5. V = 6.9V Calculation and answer (b) (iii) R = 6.9V/ 85mA = 8Ω Calculation and answer (c) (i) P = V / R P = (6.9 x 6.9) / 75 P = 0.64W Hence P is approx. 0.6W Calculation and answer (c) (ii) I = V/R I = 6.9 / 75 I = 9mA Calculation and answer 5 of

6 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 4 (a) D = C + B E = A G = A + B INPUTS INTERMEDIATE OUTPUTS C B A D E G marks for each of correct columns D & G mark for column E (b) of

7 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 Q = ( A. B ) + ( A. C) + ( A. B) Q = A (B + B ) + ( A. C) mark (X +X) = reduction mark for (+ X) = Q = A () + ( A. C) Q = A ( + C) Q = A 4 (c) Final gate is a NOT gate (Accept A ) Karnaugh map alternative OR mark for final gate A.B A. B A. B A. B C 0 0 C 0 0 mark for table with values mark for cluster mark for final gate 7 of

8 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 5 (a) (i) Log graph enables a wide range of values to be displayed on the same axis. Allow (enables values to be displayed as straight line) 5 (a) (ii) 7 lux V 0kΩ R 5 (b) X Y kω 0V mark for connections correct way round 5 (c) (i) 60 kω / (60kΩ + 0kΩ)) x V = 8V Working Answer 5 (c) (ii) R = kω to give same value at Y as switching voltage at X (: ratio) (No ecf on value) Reason / calculation Answer 5 (d) The op-amp is not ideal and will saturate above 0V Need to drop voltage Acceptable method Saturation Voltage drop Method 8 of

9 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 V 5 (e) Signal from Op Amp 0V 4 0V Lamp in independent mains circuit in correct position. Electromagnetic relay in correct position. Protection diode in correct position. N-channel MOSFET in correct position. mark mark mark mark 9 of

10 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 INPUTS OUTPUTS Tunnel Sensor T Car Sensor C Lorry Sensor L Message Display M Red Stop light R Green Go light G 6 (a) Column M marks Column G marks 6 (b) R = T +(C.L) mark for terms mark for OR Or for full expression S = T +(T.C.L) Max mark 0 of

11 MARK SCHEME GENERAL CERTIFICATTE OF EDUCATION (AS-LEVEL) ELECTRONICS ELEC JUNE 05 T 6 (c) (i) C G L T 6 (c) (ii) Allow reduced solution of