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Present Indefinite Tense

Present Simple Tense

It is used to express an action in present time, habitual or usual actions or daily event or universal fact. It is used to express an action in present time which is usually done on a regular basis. For example a student says, “I go to school”. It is a daily activity of a student to go to school, so such actions are expressed by present simple tense. Another example is, “I work in a factory”. It tells about a usual action of a person that he works in a factory on regular basis.

Rules. 1st form of verb or base verb is used as main verb in sentence.

                                         Structure of sentence – Rules

Positive Sentence
     • Subject + Main verb + Object
     • Subject + 1st form of verb (or base verb) + Object
Note: If the subject in a sentence is “he, she, it, singular or proper noun” then “s” or “es” is added to the first form of verb or base form in the sentence.
Examples.
         I write a letter.
         He gets up early in the morning.
         Sun rises in east.

Negative Sentences
   • Subject + auxiliary verb +NOT + Main verb +object
   • Subject + Do not/Does not + 1st form of verb (or base form) + object
Examples.
         I do not write a letter.
         He does not get up early in the morning.
         Sun does not rise in east.

Note: In negative sentence auxiliary verb “do or does” along with “not” is used. If the subject in a sentence is “he, she, it, singular or proper noun”, then “Does not” is used after subject in sentence. If subject is “I, we, they, you or plural” then “Do not” is used after subject in sentence. “s” or “es” is not added to main verb in negative sentence

Interrogative Sentence
   • Auxiliary verb + Subject + Main verb + Object
   • Do/Does + Subject + 1st for of verb (or base verb) + Object
Examples.
         Do I write a letter?
         Does he get up early in the morning?
         Does sun rise in east?


Note: If the subject in a sentence is “he, she, it, singular or proper noun” the sentence is started with Auxiliary verb “Does”. If the subject in a sentence is “I, we, they, you or plural” the sentence is started with auxiliary verb “Do”. “s” or “es” is not added to main verb in Interrogative sentence

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Significant Figures

All the accurately known digits and the first doubtful digit in an expression are called significant figures. Significant figures reflect the precision of a measured value of a physical quantity.

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Stopwatch

Stopwatch is a device which is used to measure a time interval of an event. Mechanical stopwatches have least count upto 0.1 seconds.

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Vernier Constant

Least Count Of Vernier Calipers is called Vernier Constant.

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Physics, Chapter 1 Notebook PTBB Exercise Questions

Chapter 1: Physical Quantities and Measurements

Q/A From The Text Book (PTBB)

Q1:  What is the difference between base quantities and derived quantities? Give three examples in each case.
Ans:
Base Quantities
Derived Quantities
Base quantities are the quantities on the basis of which all other quantities are expressed.
Examples:
Length, mass, time, electric current, temperature, intensity of light and amount of substance.
Derived quantities are the quantities which are expressed in terms of Base quantities.
Examples:
Volume, speed, force, work, energy, power and charge.

Q2: Pick out the base units from the following:
Joule, Newton, killogramme, hertz, mole, ampere, metre, Kelvin, coulomb and watt.
Ans: Kilogram, mole, ampere, metre and Kelvin are the base units.

Q3: Find the base quantities involved in each of the following derived quantities:
(a) speed                                                                 (b) volume
(c) force                                                                   (d) work
Ans:   (a) Speed:
Derived from “length and time”
(b) Volume:
Derived from “length”
(c) Force:
Derived from “Kilogram, length and time”
(d) Work:
Derived from “Mass, length and time”

Q4: Estimate your age in seconds.
Ans: My age in thirteen years. Its value in seconds is
13 years = 13 x 365 x 24 x 60 = Seconds.

Q5: What role SI units have played in the development of science?
Ans: SI units have played a very important role in the development of science. SI units are very helpful to exchange scientific and technical information at the international level.

Q6: What is meant by Vernier Constant?
Ans: Least Count Of Vernier Calipers is called Vernier Constant.

Q7: What do you understand by the zero error of a measuring instrument?
Ans: When zero Of moveable Scale does not coincide with main scale, then instrument has “Zero Error”.

Q8: Why is the correction of Zero Error necessary in a measuring  instrument?
Ans: Correction of Zero Error is necessary in measuring instrument to obtain an extreme correct value.

Q9: What is a stopwatch? What is the least count of a mechanical stopwatch you have used in the laboratories?
Ans: Stopwatch is a device which is used to measure a time interval of an event. Mechanical stopwatches have least count upto 0.1 seconds.

Q10: Why do we need to measure extremely small intervals of time?
Ans: In nature and also in Physics, there are so many phenomenon which vary with respect to the extremely small interval of time and for their experimental measurement we need very precise time measuring instrument. We need to measure extremely small interval of times to calculate the time interval of natural and artificial events.

Q11: What is meant by Significant Figures of a measurement?
Ans: All the accurately known digits and the first doubtful digit in an expression are called significant figures. Significant figures reflect the precision of a measured value of a physical quantity.

Q12: How is precision related to the significant figures in a measured quantity?
Ans:  An improvement in the quality of measurement by using better instrument increases the significant figures in the measured results. The significant figures are all the digits are known accurately and the one estimated digit.




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Zero Error of a Length Measuring Instrument

When zero Of moveable Scale does not coincide with main scale, then instrument has “Zero Error”.

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How to Estimate Your Age In Seconds

My age in thirteen years. Its value in seconds is

13 years = 13 x 365 x 24 x 60 = Seconds.

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