Summary Unit and dimensions class 11 cbse

CLASS - 11 PHYSICS SIGNIFICANT FIGURES
2- PAGE REVISION' (2.P.R) The reported result of measurement is a number
that includes all digits known with certainty
- UNITS & MEASUREMENT plus the first digit that is uncertain or
reliable.
) SySTEM OF UNITS SI UNIT RULES OF SIGNIFICANT FIGURES.

→ International System of Units (BQ) BASE
QUANTITY (UNIT) →(Symbo)|1) All non-zero digits are significant.
(SI) e.g. 5.23 , 304, -2.35 all are significant
Centimetre, gram and second 1. Length
metre m
→ CGS (2) Al zeroes between two non- Zero digits
→ FPS → Foot, pound, second
are significant.
2.. Mass kilagram kg e-g 2008 1.030→ all 2eroes are significant
→ MKS → Metre, kilogram and second (3) If the number is less than 1, the zero(s) on
3. Time Second S
the left the first non- 2ero digit are not
2) UNIT 4. Electric current ampere A significant.
e.g. 0.006,0.0098 - zeroes on left are
→ The unit of measurement is o not significant
5. Temperature kelvin K
standard quantity which is used
The trailing zero(s) in a number are significant
to measure another physical 6. Amount of mole mo if the decimal point is written.
quantity of the same kind. Substance
e.g. 2.300 , 12.3000 → zeroes are significant
→ e-g. length is measured in metre, 7. Luminous Candela cd 5) The trailing 2ero (s) in a number are not significant
mass in kilogram, time in second intensity if the decimal point is not written.
e.g. 2300, 12300 → zeroes are
not significant
ARITHMETIC OPERATION WITH SIGNIFICANT FIGURES BONUS :
3.00 (decimal given) → 3 significant figures
1) MuLTIPLICATION OR DIVISION: 300 (decimal not given) → 1 significant figure
The result should be in that number of significant figures O.0200 → 3 significant figures
which the is the least in the given data.
e.g. 6.78 x 3.6 = 24.408 → 24.4 (2 significant figures)
DIMENSIONS OF PHYSICAL QUANTITIES
3 s.f. 2s.f least s.f. = 2
2) ADDITION AND SUBTRACTION : 1) The nature of a physical quantity is described
The decimal is written as least decimal place in by its dimensions.
the given data. 2) Physical quantities are represented by derived
e.g. 2.33, 68.3, 899.73 least decimal place = tenths
place For example -
1070.36 Electric current
= 1070.3
Answer should be written Length Thermodynamic temperature
with one decimal place. Mass
Amount of Substance [N]
Time [TJ
RoUNDING OFF DIGITS (SIMPLE LANGUAGE) Luminous intensity
Rule : Look at the digit on the right of the digit you want to
keep. Definition : The dimensions of a physical quantity are


• If the digit on the right is less than 5 → ignore it. the powers (exponents) to which the base quantities
1.73 - 1.7 are raised to represent that quantity.
• If the digit on the right is 5 or more → add 1 to the left digit. For example - Area = m [Lj*
e.g. 1.76 → 1.8

Important Cases: DIMENSIONAL CONSISTENCY OF EQUATIONS
1. If the last digit is 5 → check the digit after 5. → In this, we check the correctness of an equation
• If after 5 there is any digit (not zero), then add 1.
1. 765 → 1.77
by comparing the dimensions of all terms.
For example →
If after 5 there are only zeroes or nothing, then
keep the 5 (do not change). x = Xo t Vot + at
e.g. 1.73500 → 1.735
[L] - [L] + [LT] [T] + [LT*] [r*]
2. If the last digit is 5 → and you want odd /even number
• If the digit before 5 is odd → keep 5 to make number odd.
e-g. 1. 35 → 1.735 (3 is odd)
• If the digit before 5 is even → add 1 to make number even. Since the dimensions of all terms are same,
1.745→ 1.74 (4 is even) equation is dimensionally correct.
Keep it
Simple!