Important Unit Conversions in Physics | Question-Answer, FAQS, Worksheet, MCQS, Test Paper

This article provides a detailed explanation of key concepts required for JEE, NEET, and CBSE Board Class 11 exams. It includes conceptual discussions, question-answer formats, MCQs with explanations, worksheets, and a test paper with marks distribution.

Important Unit Conversions

• Pressure Units
  • 1 bar = 10⁶ dyne/cm² = 10⁵ Nm⁻² = 10⁵ pascal
  • 76 cm of Hg = 1.013×10⁶ dyne/cm² = 1.013×10⁵ pascal = 1.013 bar
  • 1 torricelli (torr) = 1 mm of Hg = 1.333×10³ dyne/cm² = 1.333 millibar
• Velocity Conversion
  • 1 kmph = (5/18) ms⁻¹
• Force and Power Conversions
  • 1 dyne = 10⁻⁵ N
  • 1 H.P = 746 watt
• Energy and Work Units
  • 1 kilowatt-hour = 3.6×10⁶ J
  • 1 kgwt = g newton
  • 1 calorie = 4.2 joule
  • 1 electron volt (eV) = 1.602×10⁻¹⁹ joule
  • 1 erg = 10⁻⁷ joule

Conceptual Questions & Answers

Q1: Why is pressure measured in multiple units like bar, torr, and Pascal?

A: Different measurement systems and scientific applications require different units. The SI unit is Pascal, while bar and torr are often used in meteorology and laboratory experiments.

Q2: What is the significance of 1 kilowatt-hour in electricity billing?

A: 1 kilowatt-hour (kWh) represents the amount of energy consumed when a device of 1 kW runs for 1 hour. It is the standard unit used in electricity billing.

Q3: How does the conversion of kmph to m/s help in solving physics problems?

A: Many physics formulas use SI units, where velocity is in m/s. Converting kmph to m/s ensures consistency in calculations.

Multiple-Choice Questions (MCQs)

Q1: Which of the following is equivalent to 1 bar?

A) 10⁶ dyne/cm²
B) 10⁵ Nm⁻²
C) 10⁵ pascal
D) All of the above
Answer: D

Explanation: 1 bar is equivalent to all the given values as per standard conversion.

Q2: The value of 1 calorie in joules is:

A) 3.8 J
B) 4.2 J
C) 4.8 J
D) 5.2 J
Answer: B

Explanation: By definition, 1 calorie = 4.2 joules.

Q3: 1 erg is equal to how many joules?

A) 10⁻⁷ J
B) 10⁻⁵ J
C) 10⁻¹⁰ J
D) 10⁻⁸ J
Answer: A

Explanation: 1 erg is defined as 10⁻⁷ joules.

Do You Know?

• The SI unit of pressure is Pascal (Pa).
• 1 mm of Hg is called 1 Torr, named after Evangelista Torricelli.
• Horsepower (HP) is commonly used for engines but is not an SI unit.
• The erg is mainly used in the field of astrophysics and classical mechanics.

Worksheet

Section A: Conceptual Questions

1. Define 1 bar in terms of dyne/cm² and Pascal.
2. Convert 100 kmph into m/s.
3. How many joules are there in 5 electron volts?

Section B: Numerical Problems

4. A car moves with a speed of 90 kmph. Convert it into m/s.
5. Convert 500 erg into joules.

Test Paper (Marks Distribution)

Total Marks: 50

Section A (1 mark each)

1. Define 1 bar in terms of Pascal.
2. What is the value of 1 H.P in watts?

Section B (2 marks each)

3. Convert 10 kmph to m/s.
4. Write the significance of the unit “erg”.

Section C (5 marks each)

5. Explain the importance of SI units in physics with examples.
6. Solve: A device consumes 2 kW power for 3 hours. Calculate energy consumed in joules.

Important Points for Quick Revision

• 1 bar = 10⁵ pascal.
• 1 kmph = (5/18) ms⁻¹.
• 1 calorie = 4.2 J.
• 1 erg = 10⁻⁷ J.
• 1 H.P = 746 watts.

Test Your Knowledge (Quiz)

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