CBSE Class 11 Computer Science – Number Systems & Encoding Schemes

Subject Code 083 | Session 2026–27 | Free TeachGyan Study Resource

Detailed Explanation

Computers use positional number systems. Class XI includes binary, octal, decimal and hexadecimal and conversion between them. Binary uses powers of 2, octal powers of 8, decimal powers of 10 and hexadecimal powers of 16. Character encoding maps characters to numerical representations. ASCII covers a limited character set, ISCII supports Indian scripts, and Unicode provides a much broader standard; UTF-8 and UTF-32 are Unicode encoding forms.

Key Points Explained

• Learn the terminology rather than memorising isolated lines.
• Connect each rule or component with its purpose.
• Use examples to test whether you can apply the concept.
• For Python, trace the program before predicting its output.
• For theory, support answers with a relevant example or comparison.

Worked Application

Explain why Unicode is suitable for a website containing English, Kannada and Hindi text whereas a limited legacy encoding may not be.

Chapter-Specific MCQs

1. Which number system uses digits 0–9 and A–F? (A) Hexadecimal (B) Binary (C) Octal (D) Decimal.
2. Which approach best demonstrates understanding of this chapter? (A) Applying its specific rule to a new situation (B) copying an unrelated answer (C) memorising headings only (D) ignoring conditions. Answer: A.
3. When a question changes the numbers or context but tests the same principle, the student should: (A) apply the underlying concept (B) reject the question (C) memorise a new answer blindly (D) omit reasoning. Answer: A.
4. Which is most useful for checking an answer in Computer Science? (A) Testing with suitable cases (B) Guessing output (C) ignoring edge cases (D) skipping execution. Answer: A.
5. A technically strong answer should use: (A) correct terminology and reasoning (B) unrelated facts (C) only a heading (D) decorative text. Answer: A.

HOTS & Competency-Based Questions

1. Convert 45 decimal to binary and hexadecimal, showing each place-value step.
2. Construct a new real-world or programming situation in which this chapter’s main concept is necessary. Explain your reasoning.
3. Identify one common beginner mistake related to this topic and show the corrected approach.

Short-Answer Practice

1. Define three important terms from this chapter and explain each in one or two sentences.
2. Differentiate two closely related concepts from this chapter using at least three points.
3. Explain the worked application above in your own words and identify the rule or principle used.
4. Give one original example that demonstrates the chapter concept.

Long-Answer Practice

Write a structured answer covering the concept, its components or steps, one worked example, common mistakes and one application. Use a table, flowchart or code block where it improves clarity.

Practical / Programming Practice

For programming topics, write and execute at least two original programs related to this chapter. Test normal input, boundary input and an unexpected input. Record the expected output before execution and explain any difference.

Quick Revision

• Definitions and terminology
• Rules / syntax / sequence
• Worked example
• Common errors
• One competency application
• One fresh practice problem

Exam Tip

Answer the command word precisely. “Define” needs a concise meaning; “explain” needs mechanism or reasoning; “differentiate” needs paired differences; “justify” needs evidence; and programming questions require readable, logically correct code.