# ISC Electricity and Electronics Class 12 Syllabus

There is one paper of three hours duration of 100 marks. The paper is divided into two parts. Part I consists of short answer questions. This part is compulsory. Part II consists of eight questions. You are required to answer five questions.

### 1. Distribution of electric power

Idea of a simple distribution system. Mention of the local power system should be made.

Overhead and underground cables: advantages and uses. D.C and A.C distribution systems: D.C 2 wire system, 3 wire system; AC distribution transformer (3 phase 3 wire system, 3 phase 4 wire system).

### 2. The D.C. generator and motor

Use of split-ring commutators; constructional features. Shunt series and compound field connections and their characteristics. Starting of D.C. motors. Ideas on back e.m.f.

Single loop D.C. generator (circuit diagram); parts of a practical generator, lap and wave windings of armature conductors; armature reactions, commutation and period of commutation (Tc ), use of interpoles, emf equation Eg = φPN/60 × Z/A (derivation not required); types of generators;

Excitation of poles: Self-excited and separately excited; generator construction: shunt, series & compound types; no-load and load characteristics, voltage, current and power equations, critical resistance; causes of failure to build up voltage for generators, applications and simple numericals.

Motors: Working principle of a DC motor; voltage equation; significance of back emf; D.C motor characteristics. Types of D.C motor constructionsshunt, series and compound; necessity of motor starter and protective devices; power equation applications, uses and numericals.

### 3. The A.C. motor

Ideas on A.C. motors (single phase only). The rotating field. Methods of shunting: capacitance start, split phase start. Single-phase induction motor types.

A.C. motors (single phase only); idea of rotating magnetic field: split phase start, capacitor start single phase induction motor types. Uses of AC motors.

### 4. Wires, cables and electrical wiring

Construction of various types in domestic and industrial use. (Solid and stranded cables - how insulated and protected. Flexes). Selection of cable sizes, voltage drop and simple calculation on current-carrying capacity. (Linking of size of cables and flexes with maximum current flow particularly in relation to the circuits below. Regulation B 23 (voltage drop).

Brief description of the wiring systems. Simple circuitry. (Separation of lighting and power circuits. Layout of lighting circuits. Switch in phase line. Dual switching of lamps. Layout of power circuits - ring and spur/ tree systems.) types - limitations). Introduction to rules and regulations, both local and that of I.E.E. (Sequence of equipment).

Effects of overloading. Protection of circuits and individuals by (a) fuses and trips, (b) earthing of metal, (c) mechanical protection of cables. Regulations for bathrooms. Commonsense appreciation of dangerous practices (Simple testing).

Different types of insulations used in cables; Vulcanised Indian Rubber (VIR), Tough Rubber Sheathed (TRS), Poly Vinyl Chloride (PVC).

### 5. Electrical accessories

Structure and uses of various types of switches, power outlets, lamp holders, ceiling roses and junction boxes. (Familiarity with these is expected - detailed knowledge of structure is not required). Where and how they are used.

Structure and uses of switches; types: quick break knife switch, main switch, metal clad switch, air break switch, tumbler switch, piano-key switch, finger touch switch; essential qualities of a switch and its position in circuits and layouts; power outlets - Plug and Sockets; lamp holders types: bracket holder, batten holder, pendant holder, angle holder. Ceiling roses; junction boxes. Where and how they are used.

### 6. Introduction to electronics

Concept of electron flow. Common components employed in electronic circuits; resistors, capacitors and inductors; their structure, types and uses.

Concept of electron flow; passive components employed in electronic circuits. Types of Resistors: wire wound, carbon composition type, variable type (potentiometers, rheostat); colour code. Types of Inductors: air core, iron-core, ferrite core inductors.

Types of Capacitors: fixed and variable types. Fixed type: electrolytic capacitor, non-electrolytic (paper capacitors, mica capacitor, ceramic capacitors); variable type - ganged capacitors, their structure, types, voltage equations and uses.

### 7. Diodes

Thermionic diode; semiconductor diode. Structure of vacuum diode and semiconductor diode.

Thermionic diode: construction, operation characteristics of vacuum diodes; A.C and D.C plate resistances, space charge, space charge limiting region.

Semiconductor diodes: bonds in semiconductors, crystal structure of Germanium and Silicon; effect of temperature on semiconductor; concept of hole current; intrinsic and extrinsic semiconductors; doping, n-type, p type semiconductors, energy band diagrams; majority and minority charge carries; properties of p-n junction diode, forward bias and reverse bias diagrams and graphs; volt-ampere characteristics of p-n junction.

Definitions of the following: break down voltage, knee voltage, maximum forward current, Peak inverse voltage (PIV), maximum power rating.

### 8. Power supply for electronic apparatus

Mains transformer. The diode; half wave, full wave and bridge rectifiers, voltage doubler. Filters; RC filters, chokes, bleeder resistance and its functions.

Mains transformer; semiconductor diodes as half wave rectifier, full wave rectifier, bridge rectifier. Forward resistance, forward current, reverse current, derivation for: d.c (average current Idc). Root mean square (rms) current (Irms), efficiency of rectification (η); advantages, disadvantages and uses, ripple factors; simple numericals.

Voltage doublers: Types of filters: RC filter, choke Input (I/P) filter, -section filter. Input (I/P) and Output (O/P) graphs. Zener diode for voltage stabilisation, importance of series Resistor in the stabilization circuit, simple numericals. Chokes, bleeder resistors and their functions.

### 9. Vacuum triode

Structure of the vacuum triode valve. The control grid. Triode valve characteristics. Triode parameters; anode resistance, mutual conductance and amplification factors; relationship between the above parameters. Triode as a voltage amplifier. Bias voltage, cathode resistor and cathode bypass capacitor.

Structure of the vacuum triode, control grid, triode value characteristics, grid cut off voltage. Plate characteristics, mutual characteristics; vacuum tube constants (Triode parameters), relationship between them, simple numericals. Triode as voltage amplifier: bias voltage, cathode resistor and cathode bypass capacitor; current in vacuum, causes of tube failure. Significance of vacuum in tubes.

### 10. Semiconductor Transistors

The junction transistor: PNP and NPN types. Introduction to various methods of construction; their characteristics including handling procedures and precautions.

Self-explanatory.

### 11. Transistor amplifier

Introduction to the commonbase, common emitter and common collector amplifiers. Comparison of the voltage, current and power gains and input and output resistances (elementary approach only). Phase relationship. Bias stabilization.

Modes of connections: Common-Base (CB), Common-Emitter (CE), Common-Collector (CC) amplifiers: current amplification factors (α, β and 𝛾) and their relationship. Simple numericals on the above.

I/P and O/P characteristics, comparison of the voltage, current and power gain, I/P & O/P resistance (elementary approach only). Phase relationship, bias stabilization, single stage RC coupled amplifier circuit, bias circuit, emitter bypass capacitor, transistor current equation ∆ IE= ∆IB +∆IC. Phase reversal in CE mode.

### 12. The amplifier

A typical amplifier voltage and power amplification. Matching of the power output stage to a speaker.

Voltage Amplifier (RC Coupled) circuit; Power amplifier circuit, impedance matching of the power (O/P) stage to the speaker; advantages, disadvantages, frequency responses (qualitative), Applications. Differences between transistors and tubes.

### 13. Apparatus for reproducing and recording sounds

Range of hearing, recording and reproducing.

Characteristics of microphones; types of microphones: carbon, crystal, moving-coil and ribbon types. The common types of gramophone pick-ups. The earphone, crystal and magnetic tapes. The moving-coil loudspeakers; permanent magnet. Electrostatic speaker.