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
- Define 1 bar in terms of dyne/cm² and Pascal.
- Convert 100 kmph into m/s.
- How many joules are there in 5 electron volts?
Section B: Numerical Problems
- A car moves with a speed of 90 kmph. Convert it into m/s.
- Convert 500 erg into joules.
Test Paper (Marks Distribution)
Total Marks: 50
Section A (1 mark each)
- Define 1 bar in terms of Pascal.
- What is the value of 1 H.P in watts?
Section B (2 marks each)
- Convert 10 kmph to m/s.
- Write the significance of the unit “erg”.
Section C (5 marks each)
- Explain the importance of SI units in physics with examples.
- 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)
Physics Quiz
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