Physics : Nature of Physical World and Measurement : Book Back Important Questions, Answers, Solutions : Short Questions and Answer

__Nature of Physical World and Measurement | Physics__

__Short Answer
Questions__

** **

**1. Briefly explain the
types of physical quantities.**

❖
Physical
quantities are classified into two type three are fundamental and derived
quantities.

❖
Fundamental
base quantities are which cannot be expressed in terms of any other physical
quantities. These are length, mass, time electric current, temperature,
luminous intensity and amount of substance.

❖
Quantities
that can be expressed in terms of fundamental quantities are called derived
quantities. For example area, volume, velocity, acceleration, force etc.

**2. How will you measure
the diameter of the Moon using parallax method?**

❖
Once
the distance ‘D’ of a planet is determined the diameter ‘d’ angular size of the
moon can be estimated by parallax method.

❖
Two
diametrically opposite points M and N of moon are viewed through telescope from
a point A on the earth. The angle α between the two directions viewed is
measured. Then by considering MN as arc of length d of a circle with centre at
A and distance D as radius, we can write.

α
= d / D

(or)
d = α D

**3. Write the rules for
determining significant figures.**

**Rule for counting significant
figures**

**Rule and Example:**

i.
All non-zero digits are significant

*Example** :* 1342 has four significant figures

ii.
All zeros between two non zero digits are significant

*Example** : *2008 has four significant figures

iii.
All zeros to the right of a non-zero digit but to the left of a decimal point
are significant.

*Example** : *30700 has five significant figures

iv.
a) The number without a decimal point, the terminal or trailing zero (s) are
not significant.

b)
All zero are significant if they come from a measurement.

*Example** : *a) 30700 has three significant figures b) 30700 m
has five significant figures.

v.
If the number is less than 1, the zero (s) on the right of the decimal point
but to left of the first non zero digit are not significant.

*Example** : *0.00345 has three significant figures

vi.
All zero to the right of a decimal point and to the right of non-zero digit are
significant.

*Example** : *40.00 has four significant figures and 0.030400
has five significant figures

vii.
The number of significant figures does not depend on the system of units used

*Example** : *1.53 cm, 0.0153m, 0.0000153 km. all have three
significant figures.

**4. What are the
limitations of dimensional analysis?**

**Limitations of Dimensional
analysis**

1.
This method gives no information about the dimensionless constants in the
formula like1, 2………… π, e, etc.

2.
This method cannot decide whether the given quantity is a vector or a scalar.

3.
This method is not suitable to derive relations involving trigonmetric,
exponential and logarithmic functions.

4.
It cannot be applied to an equation involving more than three physical
quantities.

5.
It can only check on whether a physical relation is dimensionally correct but
not the correctness of the relation. For example using dimensional analysis, s
= ut + 1/3at^{2} is dimensionally correct relation is s = ut ½ at^{2}

^{}

**5. Define precision and
accuracy. Explain with one example.**

Accuracy
is a measure of the closeness of the measured value to the true value.

The
precision of an instrument gives the minimum value that can be measured by it.

If
a measurement is precise, that does not necessarily mean that it is accurate.
How ever if the measurement is consistently accurate, it is also precise.

**Example :** Let the
temperature of a refrigerator repeatedly measured by a thermometer be given as
10.4°C, 10.2°C, 10.3°C, 10.1°C, 10.2°C, 10.1°C, 10.1°C, 10.1°C. However if the
real temperature inside the refrigerator is 90C, we say that the thermometer is
not accurate but since all the measured value are close to 10°C, hence it is
precise.

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