Units and System of Units (SI) - UNSOLVED PRACTICE SET
Chapter: Physical World and Measurement | Topic: Units and System of Units SI
UNITS AND SYSTEM OF UNITS (SI) - UNSOLVED PRACTICE SET
Topic: Units and System of Units SI
Multiple Choice Questions
Q1. The SI unit of electric current is:
- Volt
- Ampere
- Ohm
- Coulomb
Q2. Which of the following systems of units is based on centimetre, gram, and second?
- FPS system
- MKS system
- CGS system
- SI system
Q3. The SI unit of thermodynamic temperature is:
- Celsius
- Fahrenheit
- Kelvin
- Rankine
Q4. One nanometre is equal to:
- 10⁻⁶ m
- 10⁻⁹ m
- 10⁻¹² m
- 10⁻³ m
Q5. The SI unit of luminous intensity is:
- Lumen
- Candela
- Lux
- Watt
Q6. Which of the following is NOT a coherent system of units?
- SI system
- CGS system
- MKS system
- A system where force is measured in kgf and length in metres
Short Answer Questions
Q7. Define a unit. What is meant by a "system of units"? Name the three main systems of units used historically.
Q8. Why was the SI system introduced? Give two advantages of using SI units over the CGS system.
Q9. Write the definitions of the following SI base units:
(a) Metre
(b) Kilogram
(c) Second
Q10. A student in a Delhi school measures the length of a table as 2 metres. A student in London measures the same table and records 200 cm. A student in the US records 78.74 inches. Which measurement is most convenient for scientific communication, and why?
Q11. What is meant by a "coherent" system of units? Is the SI system coherent? Explain with an example.
Q12. Convert the following:
(a) 5 km to millimetres
(b) 2 hours to milliseconds
(c) 250 g to kilograms
Long Answer Questions
Q13. Discuss the evolution of systems of units from the FPS system to the SI system. What were the drawbacks of the FPS and CGS systems that led to the adoption of SI? Explain the features that make SI a superior and universally accepted system.
Q14. Explain the definitions of the seven SI base units. How are these definitions maintained and standardised internationally? Why is it important that these standards are universal and invariant?
Q15. A group of students from different countries (India, USA, UK, Japan) are collaborating on a physics project online. They need to share measurements of force, energy, and pressure. Analyse the problems they would face if each used their country's traditional units. How does the SI system solve these problems? Discuss with specific examples.
Application-Based Problems
Q16. A student measures the following quantities in the physics lab:
Length of a wire: 250 cm
Mass of the wire: 50 g
Time for 20 oscillations: 40 s
(a) Convert all these measurements into SI units.
(b) Calculate the linear mass density (mass per unit length) of the wire in SI units.
(c) Calculate the frequency of oscillation in SI units (Hz).
Q17. The speed of light in vacuum is exactly 299,792,458 m/s. Since 1983, the metre has been defined as the distance travelled by light in 1/299,792,458 of a second.
(a) Explain why this definition makes the speed of light an exact value with no uncertainty.
(b) If a laser pulse travels from Earth to the Moon and back in 2.56 seconds, calculate the Earth-Moon distance using this definition.
(c) Why is this method of defining the metre more precise than using a physical metre bar?
Q18. In a school science fair, a student builds a model showing the "Evolution of Measurement." The model displays:
(a) The original definition of the metre (one ten-millionth of the distance from the equator to the North Pole)
(b) The platinum-iridium metre bar definition (1889)
(c) The krypton-86 definition (1960)
(d) The current light-based definition (1983)
Prepare a detailed description card for this model, explaining each definition, its limitations, and why the modern definition is superior. Include the year of adoption for each.