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Units and Measurements — Physics STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 SciencePhysicsUnits and Measurements4 Marks
Question
Read the passage given below and answer the following questions from $(i)$ to $(v)$. All engineering phenomena deal with definite and measured quantities and so depend on the making of the measurement. We must be
clear and precise in making these measurements. To make a measurement, magnitude of the physical quantity (unknown) is compared.
The record of a measurement consists of three parts, i.e. the dimension of the quantity, the unit which represents a standard quantity and a number which is the ratio of the measured quantity to the standard quantity.
  1. A device which is used for measurement of length to an accuracy of about $10^{-5}m$, is:
  1. Screw gauge
  2. Spherometer
  3. Vernier callipers
  4. Either $(a)$ or $(b)$
  1. Which of the technique is not used for measuring time intervals?
  1. Electrical oscillator
  2. Atomic clock
  3. Spring oscillator
  4. Decay of elementary particles
  1. The mean length of an object is 5cm. Which of the following measurements is most accurate?
  1. $4.9\ cm$
  2. $4.805\ cm$
  3. $5.25\ cm$
  4. $5.4\ cm$
  1. If the length of rectangle $l = 10.5\ cm,$ breadth $b = 2.1\ cm$ and minimum possible measurement by scale$ = 0.1\ cm,$ then the area is:
  1. $22.0\ cm^2$
  2. $21.0\ cm^2$
  3. $22.5\ cm^2$
  4. $21.5\ cm^2$
  1. Age of the universe is about $10^{10}$ yr, whereas the mankind has existed for $10^6$ yr. For how many seconds would the man have existed, if age of universe were $1$ day?
  1. $9.2\ s$
  2. $10.2\ s$
  3. $8.6\ s$
  4. $10.5\ s$
✓

Answer

  1. (d) Either $(a)$ or $(b)$
Explanation:
A screw gauge and a spherometer can be used to measure length accurately as less as $10^{-5}m$
  1. (c) Spring oscillator
Explanation:
Spring oscillator cannot be used to measure time intervals.
  1. (a) $4.9\ cm$
Explanation:
Given, length, $l = 5\ cm$
Now, checking the errors with each options one - by - one, we get
$\triangle\text{l}_1=5-4.9=0.1\text{cm}$
$\triangle\text{l}_2=5-4.805=0.195\text{cm}$
$\triangle\text{l}_3=5.25-5=0.25\text{cm}$
$\triangle\text{l}_4=5.4-5=0.4\text{cm}$
Error $\triangle\text{l}_1$ is least.
Hence, $4.9\ cm$ is most precise or accurate.
  1. (a) $22.0\ cm^2$
Explanation:
Area of rectangle, $A =$ Length \times Breadth
So, $A = lb = 10.5 \times 21 = 2205\ cm^2$
Minimum possible measurement of scale $= 0.1\ cm.$
So, area measured by scale $= 22.0\ cm^2$
  1. (c) $8.6\ s$
Explnation:
Magnification in time $=\frac{\text{Age of mankind}}{\text{Age of universe}}$
$=\frac{10^6}{10^{10}}=10^{-4}$
Apparent age of mankind $= 10^{-4} \times 1$ day
$= 10^{-4} \times 86400\ s$
$= 8.64s = 8.6\ s$

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