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ISC Class XII Board Specimen 2023 : Electricity and Electronics

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ISC 12th
Indian School Certificate Examination (ISC), New Delhi

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ELECTRICITY AND ELECTRONICS ---------------------------------------------------------------------------------------------------Maximum Marks: 80 Time Allowed: Three hours (Candidates are allowed additional 15 minutes for only reading the paper. They must NOT start writing during this time). --------------------------------------------------------------------------------------------------------------------- Answer all questions in Section A, Section B and Section C. The intended marks for questions or parts of questions are given in brackets [ ]. --------------------------------------------------------------------------------------------------------------------- SECTION A 16 MARKS Question 1 (i) (ii) (iii) The purpose of synchronising control in a CRO is to: (a) focus the spot on the screen. (b) lock the display of the screen. (c) adjust the amplitude of the display. (d) control the intensity of the spot. For starting a D.C. motor, a starter resistor is required because: (a) it limits the speed of the motor. (b) it limits the starting current to a safe value. (c) it starts the motor. (d) this motor is not self-starting. A single phase induction motor is: (a) self-starting. (b) not self-starting. (c) self-starting with the help of an auxiliary winding. (d) None of the above. [1] [1] [1] --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 1 (iv) (v) In an NPN transistor ___________ are the minority charge carriers. (a) free electrons (b) donor ions (c) acceptor ions (d) holes A semiconductor diode has __________________. (a) one p-n junction (b) two p-n junctions (c) three p-n junctions (d) four p-n junctions [1] [1] (vi) The material used for making the stator of an induction motor is ______________ (copper, silicon steel). [1] (vii) A multimeter cannot measure _____________. (Capacitance, resistance) [1] (viii) Inductors are _________ devices. (active, passive). [1] (ix) An earphone converts __________________. (sound energy to electrical energy, electrical energy to sound energy) [1] (x) What happens to the speed of a D.C shunt motor if the load is increased? [1] (reduces slightly, increases slightly) (xi) (xii) Match the following: [4] (a) DC generator (1) Voltage regulator (b) Zener diode (2) Centrifugal switch (c) Induction motor (3) Transducers (d) Microphone (4) Split rings State whether the following statements are True or False: (a) The insulation colour used for Live wire is yellow. (b) Minority charge carriers in a p type semiconductor are electrons. [2] --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 2 SECTION B - 32 MARKS Question 2 (i) Explain why a single phase induction motor is not a self starting machine. (ii) Answer the following questions with reference to the circuit diagram shown in Figure 1 below. IM I S [2] MAIN WINDING IS V C ROTOR STARTING WINDING Figure 1 (a) What is the use of the centrifugal switch S ? [1] (b) State the function of the capacitor C in this circuit. [1] Question 3 [4] A diagram of a semiconductor diode is shown below. Label the parts from 1 to 4 by using technical terms/names. --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 3 Question 4 (i) [4] Which one of the graphs given below, shows that the semiconductor diode is a forward biased? (a) (b) (c) (d) (ii) Name the three terminals of vacuum triode. --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 4 Question 5 [4] Name the triode parameter which can be obtained from the ratio of each of the following: (i) Change in plate current ( ) against change in grid voltage ( ) at constant plate voltage. (ii) Change in plate voltage ( ) against change in plate current ( ) at constant grid voltage. (iii) Change in plate voltage ( ) against change in grid voltage ( ) at constant plate current. (iv) write the relationship between all the three triode parameters Question 6 [4] (i) Draw a neat circuit diagram of a full wave rectifier. Also, sketch the input and output graphs. (ii) Draw a neat, labelled diagram of a crystal microphone. Question 7 [4] Name the material used in the making of the following: (i) Filament of an electric bulb. (ii) Brushes for generators and motors. (iii) Core of a transformer. (iv) connecting wires Question 8 (i) [4] (a) What is the use of a lamp holder? Mention any two types of lamp holders. (b) Write a short note on junction box. OR --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 5 (ii) (a) Briefly explain why earth pin is made thicker and longer in a three-pin plug. (b) Write a short note on ceiling rose. Question 9 (i) [4] Draw a neat circuit diagram of a transistorised voltmeter. OR (ii) Draw a neat diagram of a cathode ray tube. SECTION C - 32 MARKS Question 10 (i) With the help of a neat diagram, explain how A.C. electrical power is distributed in a 3 phase 4 wire system. [4] (ii) Write a short note on any one type of insulation used for copper wires. [2] (iii) Draw two separate diagrams to show how a dual switch can be used to turn on and off a lamp from two different places. [2] Question 11 (i) Draw a neat, labelled circuit diagram of a transistor (NPN or PNP) as an amplifier. [4] (ii) Obtain the relationship between and (symbols have their usual meaning). [2] (iii) What is the difference between active and passive circuits elements? Name any one active circuit elements. [2] --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 6 Question 12 (i) Explain how self excitation is achieved in a shunt generator. [4] (ii) A 441V shunt wound D.C. motor has armature current ( ) = 60A. If armature resistance ( ) = 0 8 , calculate: [4] (a) back emf. (b) power supplied to the armature. OR (i) State two effects of armature reaction. [2] (ii) What is meant by commutation in a D.C. motor? [2] (iii) Name the two types of generators based on excitations. [2] (iv) State the function of the following parts of a generator: [2] (a) Poles (b) Brushes Question 13 (i) With the help of a neat circuit diagram, explain the filtering action of a section filter. (ii) Draw a neat circuit diagram of a power amplifier. [8] --------------------------------------------------------------------------------------------------------------ISC SPECIMEN QUESTION PAPER 2023 7

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