FSc ICS Notes Physics XI Chapter 01 Measurements Exercise Short Questions

FSc ICS Notes Physics XI Chapter 01 Measurements Exercise Short Questions 1st Year Physics Notes Online Taleem Ilm Hub

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Question 1.1 Name several repetitive phenomenons’ occurring in nature which could serve as reasonable time standards?
Answer 1.1 Every type of natural phenomenon which is repetitive after same intervals of time acts as reasonable time standards for e.g.

1. Rotation of earth around the sun in 365 days,
2. Change of shadows of objects position of sun position of star,
3. Moon revolve around earth in 28 to 29 days.
4. Revolution of Earth around its own axis in 24 hours.

Question 1.2 Give the draw backs to use time period of a pendulum as a time standards?
Answer 1.2 Drawbacks to use time period of a pendulum as a time standard

1. Air friction can change the time period.
2. Due to increase in temperature length of pendulum increases and hence the time period increases.
3. Due to change in position from sea level gravitational acceleration changes hence time period changes.

Question 1.3 Why do we find it useful to have two units for the amount of substance, the kilogram and the mole?
Answer 1.3 It is very useful to have two units for the amount of substance i.e. kg mole.

1. Kilogram is a macro level unit it only gives the amount of substance.
2. Mole is a micro level unit one mole of substance contains the same no of molecules, no of radicals  no of atoms etc.

Question 1.4 Three students measured the length of a needle with a scale on which minimum

division is 1mm and recorded as    (1)0.2145m    (2).21m    (3).214m

which is correct and why?
Answer 1.4 In these readings option (3).214m is correct because the least count is 1m=.001mm it measures accurately up to three decimal places.


Question 1.5 An old saying is that “A chain is as strong as its weakest link” what analogous statement can you make regarding experimental data used in computation?
Answer 1.5 The analogous statement is: A given data is as much accurate as its least accurate values.

Question 1.6 The period of a simple pendulum is measured by a stop watch what type of errors are possible in the time period?
Answer 1.6 Following errors is possible in the time period:

1. Systematic error
2. Random error
3. Personal  error
4. Air friction.

Question 1.7 Does a dimensional analysis give any information on constant of proportionality that may appear in an algebraic expression? Explain.
Answer 1.7 Two answers are possible here: Yes, we can find the units of constants by using dimensional analysis (e.g.  G). If the constant is a number such as 2π and 6π, then dimensional analysis gives no information about the constant.

Question 1.8    Write the dimensions of (1) pressure and (2) density?
Answer 1.8     (1) Pressure:      P = F/A= ma/A
So [P] = [m] [a]/ [A] = [M] [LT-2]/ [L2]

[P]= [M1] [L1] [T-2] [L-2] = [M1] [L-1] [T-2]

[P] = [ML-1T-2]

(2) Density:         =m/v

[d] = [M] / [L3] = [ML-3]

[d] = [ML-3]

Question 1.9   The wavelength ƛ of a wave depends on the speed v of the wave and its
            frequency f. Knowing that               [ƛ] = [L]                [v] = [LT-1]   [f] = [T-1].
            Decide which of the following is correct.      f=v ƛ      or            f=v/ ƛ.
Answer 1.9    Given    [ƛ] = [L]                [v] = [LT-1]   [f] = [ T-1]

(i)                  f=v ƛ

[T -1]= [LT-1] [L]

Or [T -1] = [L2T-1]

As the dimension on both are not same so ( I )  is incorrect.

(ii)           f=v/ ƛ

[T -1] = [LT-1]/ [L]

[T -1] = [T-1]

As the dimension on both sides are same so formula (ii) is correct.

Written By: Asad Hussain