Distinguish between accuracy and precision? | Physics

UNITS AND MEASUREMENTS

Very Short Question Answers

Q1. Distinguish between accuracy and precision?
Ans.

Accuracy	Precision
1) It measures closeness of the measured value to the true value of quantity.	1) This is the limit up to which a quantity can be measured with the given instrument.
2) It depends on error	2) It does not depend on error.

Q2. What are the different types of errors that can occur in a measurement?
Ans.

i) Systematic errors: If the errors are always in one direction, then they are known as
systematic errors.
ii) Random errors: If the measured values differ from the true values irregularly both in
magnitude and sign, then these errors are known as random errors.
iii) Gross errors.

Q3. How systematic errors be minimised or eliminated?
Ans.

By improving experimental techniques.
By selecting better instruments.
By removing personal bias as far as possible.

Q4. Illustrate how the result of a measurement is to be reported indicating the error involved?
Ans.

As every measurement contains errors, the result of a measurement is to be reported in
such a manner to indicate the precision of measurement.
Measurement = A ± ∆𝐴 (∆A = error)

Q5. What are significant figures and what do they represent when reporting the result of a measurement?
Ans.

"The digits in a given number is the combination of the reliable digits and an uncertain digit. The combination of these two types of digits is known as significant figures. significant figures: 4"

Q6. Distinguish between fundamental units and derived units?
Ans.

Fundamental units	Derived units
The units of fundamental quantities are called fundamental units. These are independent. Ex: Metre, kilogram, Second.	The units of derived quantities are called derived units. These are derived from fundamental units. Ex: Newton, Joule

Q7. Why do we have different units for the same physical quantity?
Ans.

To measure the same physical quantity we have different units because

Depends on the magnitude of the physical quantity measured.
Different systems of measurements used. Ex. M.K.S System, C.G.S system, F.P.S
system.

Q8. What is dimensional analysis?
Ans.

Dimensional analysis is a method in which fundamental quantities are raised to suitable powers to express a physical quantity.

Ex: Force: $M^{1}L^{1}T^{-2}$

Q9. How many orders of magnitude greater is the radius of the atom as compared to that of the nucleus?
Ans.

The radius of the atom $=10^{-10} m$

The radius of the nucleus $=10^{-14} m$
Hence, the radius of the atom is $10^{4} m$ times greater than that of the nucleus.

Q10. Express unified atomic mass unit in kg?
Ans.

$https://latex.codecogs.com/svg.image?\inline \large \frac{1}{12}$ ^th of the mass of carbon isotope $_{6}^{12}\textrm{C}$

Unified atomic mass unit $1u=1.66\times 10^{-27}$

Short Question Answers

Q1. The vernier scale of an instrument has 50 divisions which coincide with 49 main scale divisions. If each main scale division is 0.5 mm, then using this instrument what would be the minimum inaccuracy in the measurement of distance?

Ans. UNITS AND MEASUREMENTS

Q2. In a system of units the unit of force is 100N, unit of length is 10m and the unit of time is 100s. What is the unit of mass in this system?

Ans. UNITS AND MEASUREMENTS

Q3. The distance of a galaxy from Earth is of the order of10²?m . Calculate the order of magnitude of the time taken by light to reach us from the galaxy?

Ans. UNITS AND MEASUREMENTS

Q4. The Earth-Moon distance is about 60 Earth radius. What will be the approximate diameter of the Earth as seen from the Moon?

Ans. UNITS AND MEASUREMENTS

Q5. Three measurements of the time for 20 oscillations of a pendulum are given as 39.6 s,39.9 s and 39.5 s . What is the precision in the measurements?What is the accuracy of the measurements?

Ans. UNITS AND MEASUREMENTS

Q6. A new unit of length is chosen so that the speed of light in vacuum is 1 unit. If light takes 8 min and 20 s to cover this distance, what is the distance between the Sun and Earth in terms of the new unit?

Ans. UNITS AND MEASUREMENTS

Q7. A student measures the thickness of a human hair using a microscope of magnification 100. He makes 20 observations and finds that the average thickness (as viewed in the microscope) is 3.5 mm. What is the estimate of the thickness of hair?

Ans. UNITS AND MEASUREMENTS

Q8. The velocity of a body is given by V=At²+ Bt + C . If v and t are expressed in SI,what are the units of A, B and C?

Ans. UNITS AND MEASUREMENTS