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__Units and Measurements MCQs __

2. Each base quantity is defined in terms of a certain basic, arbitrarily chosen but properly standardised reference standard called unit (such as metre, kilogram, second, ampere, kelvin, mole and candela). The units for the fundamental or base quantities are called fundamental or base units.

3. Other physical quantities, derived from the base quantities, can be expressed as a

combination of the base units and are called derived units. A complete set of units,

both fundamental and derived, is called a system of units.

4. The International System of Units (SI) based on seven base units is at present

internationally accepted unit system and is widely used throughout the world.

5. The SI units are used in all physical measurements, for both the base quantities and the derived quantities obtained from them. Certain derived units are expressed by means of SI units with special names (such as joule, newton, watt, etc).

6. The SI units have well defined and internationally accepted unit symbols (such as m for metre, kg for kilogram, s for second, A for ampere, N for newton etc.).

7. Physical measurements are usually expressed for small and large quantities in scientific notation, with powers of 10. Scientific notation and the prefixes are used to simplify measurement notation and numerical computation, giving indication to the precision of the numbers.

8. Certain general rules and guidelines must be followed for using notations for physical

quantities and standard symbols for SI units, some other units and SI prefixes for

expressing properly the physical quantities and measurements.

9. In computing any physical quantity, the units for derived quantities involved in the

relationship(s) are treated as though they were algebraic quantities till the desired

units are obtained.

10. Direct and indirect methods can be used for the measurement of physical quantities.

__Here are some Important MCQ on Unit and Measurement__**1. The base quantity among the following is**

(1) Speed

(2) Weight

(3) Length

(4) Area

**Answer**(3)There are seven base quantities,

(i) Mass

(ii) Length

(iii) Time

(iv) Current

(v) Amount of substance

(vi) Luminous intensity

(vii) Temperature

**2. Which of the following is not a unit of time?**

(1) Second

(2) Minute

(3) Hour

(4) Light year

__Answer (4)__Light year is the unit of distance

1 light year = 9.46 × 1015 m

**3. One astronomical unit is a distance equal to**

(1) 9.46 × 1015 m

(2) 1.496 × 1011 m

(3) 3 × 108 m

(4) 3.08 × 10¹6 m

__Answer (2)__**4. Ampere second is a unit of**

(1) Current

(2) Charge

(3) Energy

(4) Power

__Answer (2)__**5. The most precise reading of the mass of an object, among the following is**

(1) 20 g

(2) 20.0 g

(3) 20.01 g

(4) 20 × 100 g

__Answer (3)__**6. The most accurate reading of the length of a 6.28 cm long fibre is**

(1) 6 cm

(2) 6.5 cm

(3) 5.99 cm

(4) 6.0 cm

__Answer (2)__**7. Which of the following is a unit that of force?**

(1) N m

(2) mN

(3) nm

(4) N s

__Answer (2)__**8. The number of significant figures in a pure number 410 is**

(1) Two

(2) Three

(3) One

(4) Infinite

__Answer (4)__**9. Thickness of a pencil measured by using a screw gauge (least count .001 cm) comes out to be 0.802 cm. The percentage error in the measurement is**

(1) 0.125%

(2) 2.43%

(3) 4.12%

(4) 2.14%

__Answer (1)__**10. The relative error in the measurement of the side of a cube is 0.027. The relative error in the measurement of**

**its volume is**

(1) 0.027

(2) 0.054

(3) 0.081

(4) 0.046

**(3)**

__Answer__**11. Zero error in an instrument introduces**

(1) Systematic error

(2) Random error

(3) Least count error

(4) Personal error

**(1)**

__Answer__**12. A packet contains silver powder of mass 20.23 g ± 0.01 g. Some of the powder of mass 5.75 g ± 0.01 g is**

**taken out from it. The mass of the powder left back is**

(1) 14.48 g ± 0.00 g

(2) 14.48 ± 0.02 g

(3) 14.5 g ± 0.1 g

(4) 14.5 g ± 0.2 g

__Answer (2)__m1 = 20.23 g ± 0.01 g

m2 = (5.75 ± 0.01) g

m1 – m2 = [(20.23 – 5.75) ± 0.02] g

m (14.48 0.02) g

**13. The addition of three masses 1.6 g, 7.32 g and 4.238 g, addressed upto proper decimal places is**

(1) 13.158 g

(2) 13.2 g

(3) 13.16 g

(4) 13.15 g

**(2)**

__Answer__**14. We can reduce random errors by**

(1) Taking large number of observations

(2) Corrected zero error

(3) By following proper technique of experiment

(4) Both (1) & (3)

**(1)**

__Answer__**15. The number of significant figures in the measured value 0.0204 is**

(1) Five

(2) Three

(3) Four

(4) Two

**(2)**

__Answer__**16. The number of significant figures in the measured value 26000 is**

(1) Five

(2) Two

(3) Three

(4) Infinite

**(2)**

__Answer__The trailing zeros are not significant.

So, only two digits are significant.

**17. The number of significant zeroes present in the measured value 0.020040, is**

(1) Five

(2) Two

(3) One

(4) Three

**(4)**

__Answer__Zeores appearing between and after non-zero numbers are significant.

0.020040

**18. The number of significant figures in the measured value 4.700 m is the same as that in the value**

(1) 4700 m

(2) 0.047 m

(3) 4070 m

(4) 470.0 m

**(4)**

__Answer__4.700 Four significant figures.

Also, 470.0 m four significant figures.

**19. If a calculated value 2.7465 g contains only three significant figures, the two insignificant digits in it are**

(1) 2 and 7

(2) 7 and 4

(3) 6 and 5

(4) 4 and 6

**(3)**

__Answer__2.7465 g Last two digits are most insignificant.

**20. Round off the value 2.845 to three significant figures**.

(1) 2.85

(2) 2.84

(3) 2.80

(4) 2.83

**(2)**

__Answer__**21. A length 5.997 m rounded off to three significant figures is written as**

(1) 6.00 m

(2) 5.99 m

(3) 5.95 m

(4) 5.90 m

**(1)**

__Answer__**22. The order of the magnitude of speed of light in SI unit is**

(1) 16

(2) 8

(3) 4

(4) 7

**(2)**

__Answer__**23. The values of a number of quantities are used in a mathematical formula. The quantity that should be most**

**precise and accurate in measurement is the one**

(1) Having smallest magnitude

(2) Having largest magnitude

(3) Used in the numerator

(4) Used in the denominator

**Answer**(1)

**24. The dimensional formula for energy is**

(1) [MLT–2]

(2) [ML2T–2]

(3) [M–1L2T]

(4) [M L2 T]

**(2)**

__Answer__**25. The pair of the quantities having same dimensions is**

(1) Displacement, velocity

(2) Time, frequency

(3) Wavelength, focal length

(4) Force, acceleration

**Answer**(3

**26. The uncertain digit in the measurement of a length reported as 41.68 cm is**

(1) 4

(2) 1

(3) 6

(4) 8

**(4)**

__Answer__41.68 cm

**27. We can reduce random errors by**

**(1) Taking large number of observations**

(2) Corrected zero error

(3) By following proper technique of experiment

(4) Both (1) & (3)

**(1)**

__Answer__**28. The number of significant figures in the measured value 0.0204 is**

(1) Five

(2) Three

(3) Four

(4) Two

**(2)**

__Answer__The non-zero digits after the decimal places are significant.

**29. The number of significant figures in the measured value 26000 is**

(1) Five

(2) Two

(3) Three

(4) Infinite

**(2)**

__Answer__The trailing zeros are not significant.

So, only two digits are significant.

**30. The number of significant zeroes present in the measured value 0.020040, is**

(1) Five

(2) Two

(3) One

(4) Three

**(4)**

__Answer__Zeores appearing between and after non-zero numbers are significant.

0.020040

**31. The number of significant figures in the measured value 4.700 m is the same as that in the value**

(1) 4700 m

(2) 0.047 m

(3) 4070 m

(4) 470.0 m

**(4)**

__Answer__4.700 Four significant figures.

Also, 470.0 m four significant figures.

**32. If a calculated value 2.7465 g contains only three significant figures, the two insignificant digits in it are**

(1) 2 and 7

(2) 7 and 4

(3) 6 and 5

(4) 4 and 6

**(3)**

__Answer__**33. The exchange particles responsible for weak interactions are**

(1) Gluons

(2) A-mesons

(3) Photons

(4) W and Z bosons

**(4)**

__Answer__Weak interaction takes place through the exchange of BOSONS W and Z bosons

**34. Maxwell unified**

(1) Electricity with gravitation

(2) Electricity with magnetism

(3) Electromagnetism with optics

(4) Electromagnetism with weak interaction

**(3)**

__Answer__Maxwell unified electromagnetism with optics.

**35. Which of the following is not a derived force**?

(1) Tension in a string

(2) van der Waal forces

(3) Nuclear force between proton-proton

(4) Electrostatic force between proton-proton

**(4)**

__Answer__Electrostatic force between proton-proton is a fundamental force.

**36. Which one of the following does not experience strong nuclear force?**

(1) Leptons

(2) Baryons

(3) Hadrons

(4) Proton

**(1)**

__Answer__Leptons doesn't experience strong nuclear force.

**37. Which pair do not have equal dimensions?**

(1) Energy and torque (2) Force and impulse

(3) Angular momentum and Planck’s constant (4) Elastic modulus and pressure

**(2)**

__Answer__Force [MLT–2]

Impulse [MLT–1]

**38. The dimensions of Planck’s constant equals to that of**

(1) Energy (2) Momentum (3) Angular momentum (4) Power

**(3)**

__Answer__**39. The unit of length, velocity and force are doubled. Which of the following is the correct change in the other**

**units**?

(1) Unit of time is doubled

(2) Unit of mass is doubled

(3) Unit of momentum is doubled

(4) Unit of energy is doubled

**(3)**

__Answer__**40. Even if a physical quantity depends upon three quantities, out of which two are dimensionally same, then the**

**formula cannot be derived by the method of dimensions. This statement**

(1) May be true

(2) May be false

(3) Must be true

(4) Must be false

**(3)**

__Answer__This statement is completely correct. If a quantity depends upon two other quantities which are dimensionally

same then formula's validity can be checked but it can't be derived by the method of dimensions.

**41.**A : Absolute error in a physical quantity can be positive, negative or zero.

R : Absolute error is the difference in measured value and true value of physical quantity.

**(4) Absolute error is always positive as it is true value measured value **

__Answer__**42**. A : A unitless physical quantity must be dimensionless.

R : A pure number is always dimensionless.

**Answer**(2) : If a quantity doesnot have units so definitely it will be dimensionless but reverse is not true.

Pure number also dimensionless.

**43**. A : Absolute error is unitless and dimensionless.

R : All type of errors are unitless and dimensionless.

**(4)**

__Answer__Absolute error is not dimensionless rather it will having dimensions of the measured quantity.

**44**. A : Higher is the accuracy of measurement, if instrument have smaller least count.

R : Smaller the percentage error, higher is the accuracy of measurement.

**(2)**

__Answer__Higher accuracy means higher precisions.

So, error will be very smaller.

Low least count means low error and hence high accuracy.

**45.**A : In a measurement, two readings obtained are 20.004 and 20.0004. The second measurement is more

precise.

R : Measurement having more decimal places is more precise.

__(1)__

**Answer****46**. A : All physically correct equations are dimensionally correct.

R : All dimensionally correct equations are physically correct.

**(3)**

__Answer__If an equation is physically correct it has to be dimensionally correct also.

But the reverse is not true.

**47**. A : Physical relations involving addition and subtraction cannot be derived by dimensional analysis.

R : Numerical constants cannot be deduced by the method of dimensions.

**(2)**

__Answer__Those equations carrying multiplication and divisions of physical quantities can be derived but not valid for

addition or subtraction.

**. A : If displacement y of a particle executing simple harmonic motion depends upon amplitude a angular**

__48__frequency and time t then the relation y = a sin t cannot be dimensionally achieved.

R : An equation cannot be achieved by dimensional analysis; if it contains dimensionless expressions.

**(1)**

__Answer__Assertion and reason is correct and correctly explains assertion.

**49**. A : An exact number has infinite number of significant digits.

R : A number, which is not a measured value has infinite number of significant digits.

**(2)**

__Answer__**50: Light year is a unit of**

(a) time

(b) distance

(c) sunlight intensity

(d) mass

**. b) distance**

__Answer__**51: The dimensional formula for Planck’s constant is**

(a) [MLT]

(b) [ML2T-1]

(c) [M2L2T-1]

(d) [ML1T-1]

**. b) [ML2T-1] (Hint use E = hÎ½)**

__Answer__**52: The surface tension of a liquid is 70 dyne/cm. In MKS system its value is?**

(a) 70 N/m

(b) 7 ✕ 10-2 N/m

(c) 7 ✕ 102 N/m

(d) 7 ✕ 103 N/m

**. b) 7 ✕ 10-2 N/m**

__Answer__**53: The dimensions of Kinetic energy is same as that of**

(a) Force

(b) Pressure

(c) Work

(d) Momentum

**. c) Work**

__Answer__

__54: At 4° C, the density of water is equal to__(a) 10-3 kg m-3

(b) 10-2 kg m-3

(c) 10 kg m-3

(d) 103 kg m-3

**. d) 103 kg m-3**

__Answer__**55: One watt hour contains how many joules?**

(a) 3.6 ✕ 108 J

(b) 3.6 ✕ 102 J

(c) 3.6 ✕ 103 J

(d) 10-3 J

**Answer**. c) 3.6 ✕ 103 J

**56: Which of the following pairs has the same dimensions?**

(a) Specific Heat and Latent Heat

(b) Impulse and Momentum

(c) Surface Tension and Force

(d) Moment of Inertia and Torque

**. b) Impulse and Momentum**

__Answer__**57: The equation of state of some gases can be expressed as Vander wal equation i.e.**

**(P + a/v2)(V – b) = RT**

**Where P is the pressure, V is the volume, T is the absolute temperature and a, b, R are**

**constants. The dimensions of ‘a’ are:**

(a) [M1L1T-1]

(b) [M1L-5T1]

(c) [M2L5T-1]

(d) [M1L5T-2]

**. d) [M1L5T-2]**

__Answer__**58: Electron volt is a unit of**

(a) Charge

(b) Potential difference

(c) Energy

(d) Magnetic Force

**. c) Energy**

__Answer__**59: There are 20 divisions in 4 cm of the main scale. The vernier scale has 10 divisions. The least count of the instrument is**

(a) 0.05 cm

(b) 0.5 cm

(c) 5.0 cm

(d) 0.005 cm

**. d) 0.005 cm**

__Answer__