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With the increasing use of smartphones, computers, and modern appliances, understanding electronic devices has never been more important. This chapter focuses on semiconductors, the building blocks of electronic circuits.
You’ll learn about different types of semiconductors, how diodes and transistors work, and how these components are used in logic gates, amplifiers, and switching circuits. Though the topic may sound technical, it’s rooted in simple principles of physics, especially how materials conduct electricity at the atomic level. By the end of this chapter, you’ll know how basic electronic circuits are formed and how small silicon chips power the devices we use every day.
This study material for Class 12 explains the basics of Electronic Devices in an easy-to-understand way. Download the PDF as per last cbse class 12 physics syllabus to learn key concepts and prepare well for your exams.
Below we have provided the links to downloadable PDFs of class 12 science Ch 14 notes and get an in-depth explanation and understanding of the chapter.
a) Conductors, Insulators, and Semiconductors
b) Intrinsic and Extrinsic Semiconductors
c) p-n Junction Diode - A p-n junction is formed by joining p-type and n-type semiconductors. It behaves like a one-way valve for electric current.
d) Diode Applications
e) Transistor (Bipolar Junction Transistor) - A transistor is a three-layered semiconductor device with three terminals:
f) Working of Transistor - In common emitter configuration, a small input current at the base controls a larger current through the collector. Used to amplify weak signals in radios, TVs, and phones.
g) Transistor as an Amplifier - A small AC signal at the base results in a much larger AC output at the collector. This is how sound is amplified in speakers.
h) Logic Gates - Electronic circuits that follow Boolean logic.
Q1. What is a semiconductor?
Ans: A semiconductor is a material with conductivity between a conductor and an insulator, such as silicon or germanium.
Q2. Name one n-type and one p-type dopant.
Ans:
Q3. What is the direction of current in a forward-biased diode?
Ans: Current flows from the p-side to the n-side in a forward-biased diode.
Q4. What does a Zener diode regulate?
Ans: A Zener diode is used to regulate voltage in electronic circuits.
Q5. Name the three terminals of a transistor.
Ans: Emitter, Base, and Collector.
Q1. What is the difference between n-type and p-type semiconductors?
Ans:
Q2. What happens in a forward-biased p-n junction?
Ans:
The external battery pushes electrons and holes toward the junction, reducing the depletion region and allowing current to flow.
Q3. How does a transistor act as a switch?
Ans:
When a small current is applied to the base, it allows a large current to flow from collector to emitter. Without the base current, the transistor stays OFF, like a switch.
Q4. Explain the function of a rectifier.
Ans:
A rectifier converts alternating current (AC) to direct current (DC) using diodes that allow current to pass in only one direction.
Q1. Explain the working of a p-n junction diode in forward and reverse bias.
Ans:
Q2. Describe the structure and working of a transistor.
Ans:
A transistor has three layers: emitter, base, and collector.
Q3. What are logic gates? Explain with truth table.
Ans: Logic gates are circuits that perform logical operations.
🚫 Confusing n-type with p-type semiconductors
🚫 Assuming a diode conducts in both directions
🚫 Not identifying forward vs reverse bias correctly
🚫 Thinking transistors generate current — they control it
🚫 Forgetting the difference between analog (transistor amplifier) and digital (logic gate) circuits.
Chapter 14 Semiconductor Electronics forms the practical core of Physics in Class 12. With the growing role of electronics in modern life, understanding semiconductors, transistors, and logic gates is more than just exam preparation—it’s your entry into engineering, robotics, and computing fields. These well-structured notes simplify the theory, support numerical practice, and prepare you thoroughly for CBSE board exams.
Answer:
At 0 K, all electrons in a semiconductor are bound in the valence band, and there are no free electrons in the conduction band. Without any thermal energy to excite electrons across the band gap, no conduction occurs, so it behaves like an insulator.
Answer:
The depletion region is the area around the junction of a p-n diode where mobile charge carriers (electrons and holes) have diffused and recombined, leaving behind immobile ions. This region has no free charge carriers, acts as a barrier, and controls current flow in forward or reverse bias.
Answer:
A photodiode is a light-sensitive diode that operates in reverse bias. When light falls on it, it generates electron-hole pairs, increasing reverse current. It is used in light sensors, solar panels, and optical communication systems.
Answer:
As temperature increases, more electrons gain enough energy to jump from the valence band to the conduction band, increasing the number of free charge carriers. Thus, semiconductor conductivity increases with temperature, unlike metals.