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.
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explanation: “By definition, 1 calorie = 4.2 joules.” },
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explanation: “The SI unit of pressure is Pascal (Pa).” },
{ question: “6. 1 electron volt (eV) is equal to how many joules?”,
options: [“1.602×10⁻¹⁹ J”, “3.2×10⁻¹⁹ J”, “1×10⁻¹⁸ J”, “5×10⁻¹⁹ J”],
correct: 0,
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{ question: “7. 1 kmph is equal to how many m/s?”,
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correct: 0,
explanation: “1 kmph is converted using the formula 1 kmph = 5/18 m/s.” },
{ question: “8. The term ‘torr’ is named after which scientist?”,
options: [“Newton”, “Torricelli”, “Boyle”, “Pascal”],
correct: 1,
explanation: “The unit ‘torr’ is named after Evangelista Torricelli.” },
{ question: “9. What is the significance of kilowatt-hour (kWh)?”,
options: [“It is a unit of energy”, “It is a unit of power”, “It is a unit of force”, “It is a unit of velocity”],
correct: 0,
explanation: “1 kilowatt-hour represents energy consumption and is used in electricity billing.” },
{ question: “10. How many joules are there in 5 eV?”,
options: [“8.01×10⁻¹⁹ J”, “6.01×10⁻¹⁹ J”, “10.01×10⁻¹⁹ J”, “5.01×10⁻¹⁹ J”],
correct: 3,
explanation: “Since 1 eV = 1.602×10⁻¹⁹ J, for 5 eV it will be 5×1.602×10⁻¹⁹ = 5.01×10⁻¹⁹ J.” }
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