ISC 2025 Electricity and Electronics Question Paper for Class 12

About this paper

This is the ISC Class 12 Electricity and Electronics paper from the 2025 board examination, code 1225-866. It carries 80 marks and lasts three hours, with an extra fifteen minutes for reading only. All thirteen questions are compulsory. Section A has twelve very short subparts worth 16 marks, including multiple-choice items, a matching exercise and true-or-false statements. Section B has eight questions of four marks each, and Section C has four questions of eight marks each. Internal choices are given in two questions in Section B and in one question in Section C. The work covers split-phase motors, rectifiers, loudspeakers, d.c. machines, domestic cables and transistor amplifiers, including a calculation of the generated emf of a shunt generator. This copy has the questions only.

Exam

ISC Class 12

Subject

Electricity and Electronics

Year

2025

Paper code

1225-866

Maximum marks

80

Time allowed

3 hours + 15 min reading

Questions

13

Pages

8

Answers included

No, questions only

Paper pattern

• Section A

  16 marks

  Question 1 with twelve very short subparts: multiple-choice items, short answers, a matching exercise and true-or-false statements

• Section B

  32 marks

  Questions 2–9, four marks each; internal choice in two questions

• Section C

  32 marks

  Questions 10–13, eight marks each; internal choice in one question

Topics covered

• Cathode ray oscilloscope
• DC generators and motors
• Armature reaction and back emf
• Split-phase induction motors
• Half-wave rectifiers
• Moving-coil loudspeaker
• Zener voltage regulator
• Power distribution and cables
• Transistor amplifiers
• Semiconductor diodes

Questions from this paper

1. With the help of a neat circuit diagram, explain the working of a split-phase a.c. motor.
2. Draw a neatly labelled circuit diagram of a half-wave rectifier using a semiconductor diode, and sketch its output graph.
3. Explain the working of a moving-coil loudspeaker.
4. A shunt generator delivers 450 A at 230 V. The shunt-field resistance is 50 Ω and the armature resistance is 0.03 Ω. Calculate the generated emf.
5. A 120 V d.c. shunt motor draws a current of 200 A. The armature resistance is 0.02 Ω and the shunt-field resistance is 30 Ω. Calculate the back emf.
6. With reference to transistors, obtain the relationship between the current amplification factors α and β.