Units & Measurement - 2 - Free MCQ Practice Test with solutions, NEET Physics

• A physical quantity is a physical property of a phenomenon, body, or substance, that can be quantified by measurement.
• A physical quantity can be expressed as the combination of a magnitude expressed by a number – usually a real number – and a unit.
• All these given above can be expressed as explained so these are physical quantity.

► Time can be converted as t = (8 x 60) + 20s = 500 seconds
► Now speed given= 1 unit
We know speed = Distance / Time
which implies distance = Speed x Time
Hence, the distance becomes 1 x 500 = 500 units.

Length , l = 4,234 m
Breadth, b = 1.005 m
Thickness , t = 2.01 x 10^-2 m
Volume = l x b x t
⇒ V = 4.234 x 1.005 x 0.0201 = 0.0855289 = 0.0855 m³ (significant figure = 3)

There are three rules for determining how many significant figures are in a number: 

• Non-zero digits are always significant.
• Any zeros between two significant digits are significant.
• A final zero or trailing zeros in the decimal portion ONLY are significant.

Keeping these rules in mind, we can say that there are 4 significant digits.

The Measurement of a given quantity is essentially an act or result of comparison between a quantity whose magnitude (amount) is unknown, with a similar quantity whose magnitude (amount) is known, the latter quantity being called a Standard.

The relative error in a physical quantity raised to the power k is the k times the relative error in the individual quantity.

Suppose Z = A²,
Then,
ΔZ/Z = (ΔA/A) + (ΔA/A) = 2 (ΔA/A).
Hence, the relative error in A² is two times the error in A.

There are three rules on determining how many significant figures are in a number:

• Non-zero digits are always significant.
• Any zeros between two significant digits are significant.
• A final zero or trailing zeros in the decimal portion ONLY are significant.

So, keeping these rules in mind, there are 1 significant digit.

Difference in masses = 20.17 – 20.15 = 0.02 g
In subtraction, the final result should retain as many decimal places as there are in the number with the least decimal places.

The SI base units and their physical quantities are the metre for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the candela for luminous intensity, and the mole for amount of substance.

Option C is correct.

The principle of homogeneity of dimensions states that only quantities having the same dimensions (and therefore compatible units) can be added or subtracted.

Any statement that says similar (like-dimensional) quantities can be added or subtracted is therefore true. Statements that mention only addition or only subtraction are also true individually because they are specific cases of the general rule. Thus, 1, 2 and 3 are correct, while statement 4 is incorrect because it permits operations on quantities of different dimensions.

There are 20 divisions in 4 cm of main scale
⇒ 1 cm of main scale will have 20/4 = 5 divisions

Thus,  1 MSD  = 1/5 = 0.2 cm Vernier scale has 10 divisions 
Thus, L.C. = 0.2/10 = 0.02 cm 

If an equation fails this consistency test, it is proved wrong, but if it passes, it is not proved right.

Thus, a dimensionally correct equation need not be actually an exact (correct) equation, but a dimensionally wrong (incorrect) or inconsistent equation is definitely wrong.