Physical Quantity / भौतिक राशि
Any quantity that can be measured is called a physical quantity.
जिस राशि को मापा जा सकता है उसे भौतिक राशि कहते हैं।
Examples:
Length / लंबाई
Mass / द्रव्यमान
Time / समय
Temperature / तापमान
Force / बल
SI System
SI stands for:
International System of Units
SI का अर्थ है:
अंतरराष्ट्रीय मात्रक प्रणाली
Seven SI Base Quantities
Length
Unit: metre (m)
Mass
Unit: kilogram (kg)
Time
Unit: second (s)
Electric Current
Unit: ampere (A)
Temperature
Unit: kelvin (K)
Amount of Substance
Unit: mole (mol)
Luminous Intensity
Unit: candela (cd)
Derived Units / व्युत्पन्न मात्रक
Area
SI unit:
m²
Volume
m³
Speed
m/s
Acceleration
m/s²
Force
newton (N)
1 newton
1 N = 1 kg·m/s²
Work and Energy
SI unit:
joule (J)
1 joule = 1 newton metre
1 J = 1 N·m
Power
SI unit:
watt (W)
1 W = 1 J/s
Pressure
SI unit:
pascal (Pa)
1 Pa = 1 N/m²
Frequency
SI unit:
hertz (Hz)
1 Hz means one cycle per second.
1 Hz का अर्थ प्रति सेकंड एक चक्र है।
Electric Charge
Unit:
coulomb (C)
Potential Difference
Unit:
volt (V)
Resistance
Unit:
ohm (Ω)
Common Prefixes
kilo = 10³
centi = 10⁻²
milli = 10⁻³
micro = 10⁻⁶
nano = 10⁻⁹
mega = 10⁶
giga = 10⁹
Important Conversions
1 km = 1000 m
1 m = 100 cm
1 cm = 10 mm
1 kg = 1000 g
1 hour = 3600 seconds
1 litre = 1000 mL
Measurement Errors
No measurement is perfectly exact.
कोई भी मापन पूरी तरह त्रुटिरहित नहीं होता।
Important concepts include:
Accuracy / शुद्धता
Precision / परिशुद्धता
Least Count / अल्पतमांक
Least Count
Least count is the smallest value that a measuring instrument can measure directly.
अल्पतमांक वह सबसे छोटी राशि है जिसे कोई उपकरण सीधे माप सकता है।
Science Practice — 30 Questions
Q1
SI unit of length is:
Answer: metre
Q2
SI unit of mass is:
Answer: kilogram
Q3
SI unit of time:
Answer: second
Q4
SI unit of temperature:
Answer: kelvin
Q5
SI unit of electric current:
Answer: ampere
Q6
SI unit of luminous intensity:
Answer: candela
Q7
SI unit of amount of substance:
Answer: mole
Q8
SI unit of force:
Answer: newton
Q9
SI unit of work:
Answer: joule
Q10
SI unit of power:
Answer: watt
Q11
SI unit of pressure:
Answer: pascal
Q12
SI unit of frequency:
Answer: hertz
Q13
1 N equals:
A. kg m/s
B. kg m/s²
C. kg/m²
D. J/s
Answer: B
Q14
1 watt equals:
Answer: 1 joule/second
Q15
1 pascal equals:
Answer: 1 N/m²
Q16
1000 metres equal:
Answer: 1 kilometre
Q17
1 metre equals:
Answer: 100 centimetres
Q18
1 centimetre equals:
Answer: 10 millimetres
Q19
1 kilogram equals:
Answer: 1000 grams
Q20
1 hour equals:
Answer: 3600 seconds
Q21
“Kilo” represents:
A. 10²
B. 10³
C. 10⁶
D. 10⁻³
Answer: B
Q22
“Milli” represents:
Answer: 10⁻³
Q23
“Micro” represents:
Answer: 10⁻⁶
Q24
“Nano” represents:
Answer: 10⁻⁹
Q25
“Mega” represents:
Answer: 10⁶
Q26
Unit of speed is:
Answer: m/s
Q27
Unit of acceleration is:
Answer: m/s²
Q28
Smallest directly measurable value of an instrument is called:
Answer: Least Count / अल्पतमांक
Q29
Closeness of measured value to the true value is called:
Answer: Accuracy / शुद्धता
Q30
Closeness among repeated measurements is related to:
Answer: Precision / परिशुद्धता