Practical Units of Length, Mass, Time-JEE, NEET, Class 11 Physics | Explanations, FAQs, MCQs, Worksheets

Introduction

Prepare for JEE, NEET, and CBSE Board Class 11 exams with our comprehensive study material, including FAQs, MCQs, explanations, and worksheets. Get high-quality learning resources at Anand Technical Publishers.

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Practical Units of Length, Mass and Time

1. Length

• 1 fermi = 1 fm = 10⁻¹⁵ m
• 1 X-ray unit = 1XU = 10⁻¹³ m
• 1 angstrom = 1Å = 10⁻¹⁰ m = 10⁻⁸ cm = 10⁻⁷ mm = 0.1 μm
• 1 micron = 1 μm = 10⁻⁶ m
• 1 astronomical unit = 1 A.U. = 1.49 × 10¹¹ m ≈ 1.5 × 10¹¹ m ≈ 10⁸ km
• 1 Light year = 1 ly = 9.46 × 10¹⁵ m
• 1 Parsec = 1 pc = 3.26 light years

2. Mass

• Chandra Shekhar unit = 1 CSU = 1.4 × mass of the sun = 2.8 × 10³⁰ kg
• Metric tonne = 1 Metric tonne = 1000 kg
• Quintal = 1 Quintal = 100 kg
• Atomic mass unit (amu) = 1 amu = 1.67 × 10⁻²⁷ kg

3. Time

• Year: Time taken by Earth to complete 1 revolution around the Sun in its orbit.
• Lunar month: Time taken by the Moon to complete 1 revolution around Earth. 1 L.M. = 27.3 days
• Solar day: Time taken by Earth to complete one rotation about its axis with respect to the Sun. 1 Solar year = 365.25 average solar days
• Siderial day: Time taken by Earth to complete one rotation about its axis with respect to a distant star. 1 Solar year = 366.25 Siderial days = 365.25 average solar days
• Shake: An obsolete but practical unit of time. 1 Shake = 10⁻⁸ sec

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FAQs on Practical Units of Length, Mass and Time

Q1: What is a light year?

A1: A light year is the distance that light travels in one year, approximately 9.46 × 10¹⁵ meters.

Q2: What is an astronomical unit (A.U.)?

A2: One astronomical unit is the average distance from Earth to the Sun, approximately 1.49 × 10¹¹ m.

Q3: How is an atomic mass unit (amu) defined?

A3: One atomic mass unit (amu) is defined as 1.67 × 10⁻²⁷ kg, roughly the mass of a proton or neutron.

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MCQs on Practical Units of Length, Mass and Time

Q1: Which of the following is the largest unit of distance?

• (A) Angstrom
• (B) Parsec
• (C) Light year
• (D) Astronomical Unit
  Answer: (B) Parsec
  Explanation: A parsec is approximately 3.26 light years, making it the largest unit of distance in astronomy.

Q2: How many kilograms are there in one metric tonne?

• (A) 10 kg
• (B) 100 kg
• (C) 1000 kg
• (D) 10,000 kg
  Answer: (C) 1000 kg
  Explanation: One metric tonne is equal to 1000 kg.

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Worksheet on Practical Units of Length, Mass and Time

1. Convert the following values:
   • (a) 5 A.U. to meters
   • (b) 2 metric tonnes to kilograms
   • (c) 3 parsecs to light years
2. Fill in the blanks:
   • (a) 1 light year = ___ meters.
   • (b) 1 fermi = ___ meters.
   • (c) The time taken by the Earth to complete one revolution around the Sun is called ___.

For comprehensive study materials, worksheets, and practice questions for JEE, NEET, and CBSE Board Class 11 exams, visit Anand Technical Publishers.

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