Physical Quantities Flashcards
What is a unit?
A standard physical quantity taken as a reference to express the physical quantity is called unit.
(Unit for fundamental quantity is called fundamental unit.)
How many fundamental quantities are there?
7
What is the unit for luminous intensity?
Candela
What is dimensional analysis?
The power raised to the fundamental quantity to express the physical quantity is called dimensional analysis.
What is fundamental quantity and fundamental unit in the example?
Length - Meter
Mass - Kilogram
Time - Second
Fundamental quantities = Length, Mass, Time
Fundamental units = Meter, Kilogram, Second
What are the two supplementary quantities?
Angle - Radian
and
Solid angle - Steradian
What is dimensional formula?
The representation of how fundamental units are involved in the unit of a physical quantity is called dimensional formula.
What is the dimension of energy ?
[M L^2 T^2]
What is the dimension of coefficient of viscoucity?
[ M L^-1 T^-1 ]
What is the dimension of specific heat capacity?
[ M^0 L^2 T^-2 K^-1 ]
Formula for viscoucity is?
F = 6 π η r v ,
where
η = coefficient of viscoucity
r = radius of the sphere
v = velocity of the sphere
Do physical quantity always has dimension?
They may or may not have dimension
What is dimensional variable?
These are the quantities which are variable and have dimensions as well.
For example; velocity, momentum, force
What is the dimension of specific latent heat capacity?
[ M L^2 T^-2 ]
What are dimensional constants?
These are the quantities which have constant values and yet have dimensions.
dimensions. For example; gravitational constant, coefficient of viscosity, Planck’s constant, velocity of light etc.
What re non-dimensional Variables?
These are variable quantities and have no dimensions. They are typically ratio of two similar physical quantities.
For example; specific gravity, strain, angle
What are dimensionless constants?
These are numbers like 2, 3, 4, π. The numerical value of dimensionless physical quantities remains unchanged in any system of units
What are the statements of principle of homogeneity?
- For any correct physical relation, the dimensions of each term on L.H.S. are equal to the dimensions of each term on R.H.S.
- Two physical quantities can be added or subtracted only when their dimensions are same.
What does principle of homogeneity state?
Principle of homogeneity states that an equation is dimensionally correct when dimensions each term on the either side of the equation are same.
What is the dimension of gravitational constant?
[ M^-1 L^3 T^-2 ]
What is accuracy?
The accuracy of a measurement is the measure of how close is the measurement to the true value.
What is precision?
The resolution or the limit of a measurement is precision.
What are some of the types of error during measurement?
- Instrumental error
- Imperfection in experimental technique
- Personal errors
- Random error
- Least count error
What is absolute error of an instrument?
The magnitude of the difference of true magnitude to the individual measured value is absolute error of the instrument.
i.e. |△a|
What are the main advantages of SI system?
- Universally accepted standard system
- Coherent system i.e. the unit of any physical quantity can be obtained by multiplying or dividing fundamental units without introducing numerical values.
- Rational system i.e. all forms of energy like heat light electrical energy are measured in Joule.
- It is instrumental in both theoretical and practical works.
Latent heat =
( Heat energy / Mass ) [ L^2 T ^-2]
Charge =
I * t [ A T ]
Angular velocity =
Angle / Time [ M^0 L^0 T^-1 ]
Angular acceleration =
Angle / angular velocity [ M^0 L^0 T^-2 ]
Young’s Modulus =
Stress / Strain [ M L^-1 T^-2 ]
Restrictions when deriving relationship between physical quantities using dimensions.
- Only relation between a quantity and one term can be expressed.
A = f * g (Only this can be expressed)
A = f + g (Not this)
What is precision? R = Repetition
The degree of repetition of observed values is called precision of the measurement. Not concerned with standard value rather only with the observed values.
Closeness of observations with each other
What is accuracy?
The degree of closeness of observed values to the standard value is called accuracy of the measurement. Concerned with the standard value.
Can the observations be precise but not accurate?
Yes
Can the observations be accurate but not precise?
No
If the range of observations is great than the precision is?
Low
If the range of observations is low than the precision is?
High
The more the observations are close to the standard value the greater is the?
Accuracy
The less the observations are close to the standard value the less is the?
Accuracy
Rules for significant figures :
- Non zero digits are significant
- All digits between non zero digits are significant
3.Trailing zeros after decimal points are significant - Trailing zeros without decimal points are non significant
5.Leading zeros with or without decimal points are non-significant. - Power of 10 is insignificant.
Significant figures doesn’t depend upon?
Unit of measurement : Kg, g , m , cm
No of significant figures in 2600 is?
SF : 2 (Trailing zeros are non significant)
No of significant figures in 26.00 is?
SF : 4 (Trailing zeros after decimal points are significant)
No of significant figures in 0012 is?
SF = 2 (leading zeros are non-significant)
No of significant figures in 0.013 is?
SF = 2 (leading zeros after decimal points are non-significant)
No of significant figures in 6* 10^8 and 6.1* 10^8?
1 and 2 ( Power of 10 is non significant)
What do you mean by rounding off?
The process of reshaping the value by dropping the digit(s) in such a way that the result obtained is least deviated from the original value is rounding off.
Rules for rounding off : ( even ma xodne odd ra 0 ma jodne )
- If the digit is greater than 5 - Add 1 in preceding digit.
- If the digit is less than 5 - leave the preceding digit as it is.
- If the ending digit is 5 and odd then add 1 to the preceding digit.
- If the ending digit is 5 and even then leave as it is.
5.If the ending digit is 0 then add 1 to the preceding digit. - If 5 is followed by any non zero number then add 1 to the preceding digit.
Rules for addition, subtraction, multiplication and division [Quota System]
For addition and subtraction
- Decimal point paxi ko digits herne
For multiplication and division
- No of significant figures herne.
Stress =
Force/Area
Moment of inertia =
Mass * (distance)^2
[ M L^2 T^0 ]
Size of nucleus:
Size of atom :
Size of nucleus = Fermi = 10^-15
Size of atom = Angstrom = 10^-10
Uses of Dimensional Equation :
- To find dimensions of constants in a given physical equation.
- To convert values of physical quantities from one system to another.
- To check the correctness of a physical equation.
- To derive relationship between physical quantities.T
To quantify any physical quantity, what is needed?
-nu
n = number of times the unit is contained
u = unit of the physical quantity
Fact about dimension and unit :
- Dimension remain same irrespective of the unit
1 Joule (Energy) =
10^7 erg
1 Newton (Force) =
10^5 Dynes
