11th Class Physics Physical World / भौतिक जगत Question Bank

done Units and Measurements Conceptual Problems Total Questions - 50

• question_answer1)
  What is the necessity of selecting some units as fundamental units?
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• question_answer2)
  How is SI a coherent system of units?
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• question_answer3)
  In defining the standard of length, (the prototype metre), we have to specify the temperature at which the measurement should be made. Are we justified in calling length a fundamental quantity, if another physical quantity (temperature) has to be specified in choosing a standard?
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• question_answer4)
  Do \[\overset{\text{o}}{\mathop{\text{A}}}\,\] and AU stand for the same unit of length?
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• question_answer5)
  Why is it convenient to express the distances of stars in terms of light year rather than in metre or kilometre?
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• question_answer6)
  Comment on the statement: "To define a physical quantity for which no method of measurement is given or known has no meaning."
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• question_answer7)
  Is the measure of an angle dependent upon the unit of length?
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• question_answer8)
  What is meant by angular diameter of the moon? What is its value?
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• question_answer9)
  For a given base line, which will show a greater parallax - a distant star or a nearby star?
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• question_answer10)
  Why is parallax method not useful for measuring the distances of stars more than 100 light years away?
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• question_answer11)
  What is the difference between mN, Nm and nm?
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• question_answer12)
  Do all physical quantities have dimensions? If no, name three physical quantities which are dimensionless.
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• question_answer13)
  If 'slap' times speed equals power, what will be the dimensional equation for 'slap'?
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• question_answer14)
  Write the dimensions and SI unit of linear momentum.
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• question_answer15)
  What is the basis of the principle of homogeneity of dimensions?
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• question_answer16)
  If \[~x\text{ }=\text{ }a\text{ }+\text{ }bt+c{{t}^{2}},\] where \[x\] is in metre and t in second; then what is the unit of c?
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• question_answer17)
  What are the dimensions of a and b in the relation: \[~\mathbf{F}\text{ }=a+bx,\] where F is force and \[x\] is distance?
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• question_answer18)
  Name two physical quantities having the dimensions \[[M{{L}^{2}}{{T}^{-2}}]\].
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• question_answer19)
  Write three physical quantities having dimensions \[[M{{L}^{-1}}{{T}^{-2}}]\]
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• question_answer20)
  If the units of force and length each are doubled, then how many times would the unit of energy be affected?
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• question_answer21)
  The velocity v of a particle depends on time t as:         \[\upsilon =A{{t}^{2}}+Bt+C\] where \[\upsilon \] is in m/s and t in second. What are the units of A, B and C?
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• question_answer22)
  Can a quantity have dimensions but still has no units?
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• question_answer23)
  Can a quantity have different dimensions in different systems of units?
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• question_answer24)
  Can a quantity have units but still be dimensionless?
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• question_answer25)
  Does the magnitude of a physical quantity depend on the system of units chosen?
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• question_answer26)
  Justify L + L = L and L - L = L.
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• question_answer27)
  Can there be a physical quantity that has no units and no dimensions?
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• question_answer28)
  Can an instrument be called precise with-out being accurate? Can it be accurate without being precise?
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• question_answer29)
  Which of the following length measurements is (i) most precise and (ii) least precise? Give reason (i) \[l\mathbf{ =5cm}\] (ii) \[l\mathbf{=5}\mathbf{.00cm}\] (iii) \[\mathbf{5}.\mathbf{000}\text{ }\mathbf{cm}\] (iv) \[\mathbf{5}.\mathbf{000}\text{ }\mathbf{cm}\] (\[\upsilon \])\[~\mathbf{5}.\mathbf{00000}\text{ }\mathbf{cm}\].
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• question_answer30)
  Which of the following readings is the most accurate : (i) \[\mathbf{~5000 m}\] (ii) \[\mathbf{5\times 1}{{\mathbf{0}}^{\mathbf{2}}}\mathbf{m}\] (iii) \[\mathbf{5\times 1}{{\mathbf{0}}^{\mathbf{3}}}\mathbf{m}\]?
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• question_answer31)
  Which quantity in a given formula should be measured most accurately?
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• question_answer32)
  Which of the following measurements is more accurate and why? (a) \[\mathbf{0}\mathbf{.0002 g}\]     (b) \[\mathbf{20}\mathbf{.0 g}\]
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• question_answer33)
  Why do we treat length, mass and time as basic or fundamental quantities in mechanics?
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• question_answer34)
  \[SI\] is a rational system of units while mks system is not so. Justify.
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• question_answer35)
  Why it became necessary to redefine metre on atomic standard?
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• question_answer36)
  What are the advantages of defining metre in terms of the wavelength of light radiation?
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• question_answer37)
  Give reasons why is platinum iridium alloy used in making prototype metre and kilogram.
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• question_answer38)
  Suggest a distance corresponding to each of the following order of length: (i) \[{{10}^{7}}\mathbf{m}\]     (ii) \[\mathbf{1}{{\mathbf{0}}^{\mathbf{4}}}\mathbf{m}\]  (Hi) \[{{10}^{2}}\mathbf{m}\]  (iv) \[\mathbf{1}{{\mathbf{0}}^{\mathbf{-}}}^{\mathbf{3}}\mathbf{m}\] (v) \[\mathbf{1}{{\mathbf{0}}^{\mathbf{-6}}}\mathbf{m}\]   (vi) \[\mathbf{1}{{\mathbf{0}}^{\mathbf{-14}}}\mathbf{m}\].
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• question_answer39)
  Suggest an indirect method for measuring the height of a tree on a sunny day.
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• question_answer40)
  What is the basic principle of alpha particle scattering method for estimating the size of the nucleus?
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• question_answer41)
  If the velocity of light is taken as the unit of velocity and one year as the unit of time, what must be the unit of length? What is it called?
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• question_answer42)
  What is common between bar and torr?
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• question_answer43)
                                       Distinguish between accuracy and precision.                                                              
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• question_answer44)
  Which of the following measurements is most accurate and which is most precise : (i)  4.00mm      (ii) 4.00 cm    (iii) 4.00 m       (iv) 40.00 m?
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• question_answer45)
  Two clocks are being tested against a standard clock located in a national laboratory. At 12:00:00 noon by the standard clock, the readings of the two clocks are:  

  Day	Clock 1	Clock 2
  Monday	\[\text{12}:00:0\text{5}\]	\[\text{1}0:\text{15}:0\text{6}\]
  Tuesday	\[\text{12}:0\text{1}:\text{15}\]	\[\text{1}0:\text{14}:\text{59}\]
  Wednesday	\[\text{11}:\text{59}:0\text{8}\]	\[\text{1}0:\text{15}:\text{18}\]
  Thursday	\[\text{12}:0\text{1}:\text{5}0\]	\[\text{1}0:\text{15}:0\text{7}\]
  Friday	\[\text{11}:\text{59}:\text{15}\]	\[\text{1}0:\text{14}:\text{53}\]
  Saturday	\[\text{12}:0\text{1}:\text{3}0\]	\[\text{1}0:\text{15}:\text{24}\]
  Sunday	\[\text{12}:0\text{1}:\text{19}\]	\[\text{1}0:\text{15}:\text{11}\]

      If you are doing an experiment that requires precision time interval measurements, which of the two clocks will you prefer?
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• question_answer46)
  For the determination of ?g? using a simple pendulum, measurements of \[l\]and \[T\] are required. Error in the measurement of which of these will have larger effect on the value of ?g? thus obtained and why? What is done to minimize this error?
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• question_answer47)
  Magnitude of force F experienced by a certain object moving with speed \[\upsilon \] is given by \[F=K{{\upsilon }^{2}}\], where \[K\] is a constant. Find the dimensions of \[K\].
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• question_answer48)
  The SI unit of energy is\[J=kg{{m}^{2}}{{s}^{-2}},\]that of speed \[\upsilon \] is \[\mathbf{m}{{\mathbf{s}}^{-\mathbf{1}}}\]and acceleration a is \[\mathbf{m}{{\mathbf{s}}^{-\mathbf{2}}}\]. Which of the formulae for kinetic energy (K) given below can you rule out on the basis of dimensional arguments (m stands for the mass of the body) : (a) \[K={{m}^{2}}{{\upsilon }^{3}}\]       (b) \[K=\left( 1/2 \right)m{{\upsilon }^{2}}\] (c) \[~K=ma\]           (d) \[~K=\text{ }(\mathbf{3}\text{ }/16)m{{\upsilon }^{2}}\] (e) \[K=(\mathbf{1}/\text{ 2})m{{\upsilon }^{2}}+\text{ }ma\]
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• question_answer49)
  Using the principle of homogeneity of dimensions, find which of the following is correct: (i) \[{{T}^{2}}=4{{\pi }^{2}}{{r}^{2}}\]                       (ii) \[{{T}^{2}}=\frac{4{{\pi }^{2}}{{r}^{3}}}{G}\]  (iii) \[{{T}^{2}}=\frac{4{{\pi }^{2}}{{r}^{3}}}{GM}\] where T is time period, G is gravitational constant, M is mass and r is radius of orbit.
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• question_answer50)
  The mean value of period of oscillation of a simple pendulum in an experiment is\[\mathbf{2}.\mathbf{825}\text{ }\mathbf{s}\]. The arithmatic mean of all the absolute errors is\[\mathbf{0}.\mathbf{11}\text{ }\mathbf{s}\]. Round off the period of simple pendulum to appropriate number of significant figures. Give reasons.
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