Ch#1: Physical Quantities and Measurements Flashcards
Learn about measurements , motion , torque , gravitation , work and energy , properties of matter and thermal properties of matter
What is Science? , State the branches of science.
The knowledge gained from observations and experimentations is called Science.Until the 18th century , various aspects of material objects were studied under a single subject called Natural Philosophy.As knowledge increased , it was divided into Physical and Biological sciences.Physical Science s is the study of non living things and Biological sciences is the study of living things.Physical Sciences branch into Physics , Chemistry , Astronomy , Geology and Meteorology.
What are physical quantities? Describe with an example.
All measurable quantities are called physical quantities such as length , mass and time. A physical quantity possesses atleast 2 characteristics in common. One is the numerical magnitude and the other is the unit in which it is measured. When we say we have 4kg of sugar. 4 is the numerical magnitude and kg is the unit. It would be meaningless to state only 5 or only kg.
Describe base and derived quantities.
Base Quantities :
There are seven physical quantities which form the foundation of other physical quantities. These are called base quanties. They include length , mass , time , electric current , temperature , intensity of light and amount of a substance. They are the quantites on the basis of which other quantites are expresses.
Derived Quantities: The physical quantites expressed in terms of base quantities are called derived quantities. These include area , volume , speed , force , velocity , density , etc. They are quantities expressed in terms of base quantites.
What are SI Units and why are they used?
With the developments in the field of science and technology , the need for a commonly acceptable system of units was seriously felt all over the world. The eleventh general conference on weight and measures held in Paris in 1960 adopted a worldwide system of measurement called the International System of Units.The International System of Units is commonly referred to as SI Units.
Differ between base and derived units.Also give examples.
Base Units. The units which describe base quantites are called bade units. Each base quantity has its own SI Unit. Name : Unit 1. Length : metre 2. Mass : kilogram 3. Time : second 4. Electric current : Amphere 5. Intensity of light : candela 6. Temperature : Kelvin 7. Amount of a substance : mole
Derived Units: The units used to measure derived quantities are called derived units. Derived units are defined in terms of base units and are obtained by multiplying or dividing one or more base units with each other. The unit of area and volume are based on the unit of length metre. Name : Unit Speed : m/s1 Acceleration : m/s2 Volume :m3 Pressure : Pascal Density :Kg/m3 Charge :coulomb
What prefixes and why do we use them.?
Some quantities are very large or very small such as 2000000g or 0.00002W. Si Units have the advantage that their multiples and sub multiples can be expressed in terms of prefixes. Prefixes are words or letters added before SI units such as kilo, mega, giga, etc.
Double prefixes are not used, for example, no prefix is used with kilogram because kilo is already a prefix.
What is scientific notation and why is it useful?
A simple but scientific way to write very large or small quantities is to express them in scientific notation. This saves us from having to interpret a large number of zeros and improves readability.
In scientific notation, a number is expressed by some power of 10 multiplied by a number between 1 and 10.
The number which has only one digit before the decimal point is taken as the standard form.
What are measuring instruments.? What are metre rule and measuring tapes.
Measuring instruments are used to measure physical quantities such as length, mass, time, etc.
Metre Rule:
A metre rule is a length measuring instrument used commonly in laboratories to measure length of an obkect or distsnce between two points. It is one metre long which is 100 centrimeters. Each centimeter 10 further divisions called millimeters. So one millimeter is the smallest reading that can be taken with a metre rule. It is the least count of the metre rule.
While measuring length, our eye must be positioned verticslly above the reading point. The reading becomes doubtful if our eye is positioned to the left or right.
The measuring tape:
The measuring tape is used to measure length in centimetres and metres. A measuring tape consists of a thin long strip of cotton, metal or plastic. They are generally 10, 20, 50 or 100m long. They are marked in cm and inches.
Explain the construction and working of a Vernier Callipers. (draw diagram)
Vernier Callipers :
The accuracy obtained from measurements using a metre is upto 1mm but greater accuracy can be obtained by using some other instruments such as a Vernier Callipers.a Vernier Callipers consists of two jaws. One is a fixed jaw with a main scale attached to it and the other is a movable jaw. The main scale has centimeter and millimeter markings. The movable jaw has a vernier scale having 10 divisions attached to it such that each division is 0.9mm. The difference between a vernier scale and main scale division is 0.1mm which is the least count of the vernier callipers. It can also be found by:
Least count = smallest reading on main scale/No. Of divisions on vernier scale
Least count = 1mm/10
Least count = 0.1mm
Working of a Vernier Calliper : First of all , find the error , if any in the measuring instrument. It is called the Zero Error of the measuring instrument. Knowing the zero error , necessary corrections can be made to find the correct measurement.Such a correction is called zero correction. Zero correction is the negative of Zero Error.
To find the zero error , close the jaws of the vernier callipers gently. If the zero line of the Vernier scale coincides with the zero of the main scale then zero error is zero.Zero error will exist if the vernier scale zero doesnt coincide with main sclae zero. Zero error will be positive if the zero of the zero of vernier is on the right of the main scale zero. Zero error will be negative if the vernier scale on the left of the main scale zero.
Zero Error = number of vernier scale division coinciding with main scale X Least count
Explain the construction and working of a screw gauge.(draw diagram)
A screw gauge is a length measuring instrument that is used to measure lengths at a accuracy greater than a vernier callipers. It is also called a Micrometer screw gauge. A screw gauge consists of a U shaped metal frame with a stud on its one end. A hollow cylinder or sleeve has a millimeter scale over it along a line called the index line. The hollow cylinder acts as a nut. It is fixed st the end of U shaped frame opposite to the stud. A thimble has threaded spindle inside it. As the thimble completes one rotation , the spindle moves 1mm along the index line. This is because the distsnce between the consecutive threads on the spindle is 1mm. This distance is called the pitch of the svrew gauge.
The thimble has 100 around its one end. This is the circular scale of the screw gauge. As the thimble completes one rotation , 100 divisions pass the index line and the thimble moves 1mm along the index line. Thus each division of the circular scale causes the thimble to move 0.01mm along the main scale. This is the least count of the screw gauge. Least Count can also be found by ,
Least count = pitch/no. of divisions.
Least count = 1mm/100
Least count = 0.01m
Working of a screw gauge:
To find the zero error , close the gap between the stud and the spindle by rotating the ratched in the clockwise direction. If the zero of the circular scale coincides with the index line , then the zero error will be zero.
Zero error will be positive if the zero of the circular scale is behind the index line. In this case , multiply the number of divisions of the circular scale behind the index lines by the least count of the screw gauge to find the zero error.
Zero error will be negative if zero of the circular scale has crossed the index line. In this case , multiply the number of divisions which have passed the index line by the least count od the screw gauge to get the zero error.
What are stopwatches? Differ between mechanical and digital stopwatches.
A stopwatch is used to measure the time interval of an event. There are two types of stopwatches. Mechanical and digital stopwatches. A mechanical stopwatch can measure a time interval as small as 0.1s. Digital stopwatches are commonly used in labs and they can measure a time interval as short as 1/100th of a second.
How to use one :
A mechanical stopwatch has a knob which is used to wind the spring that powers the watch. It can also be used as a start/stop button. The watch starts on the first press of the knob , it stops on the second press and the third oress brings the needle back to its original position.
The digital stopwatch starts to indicate the time elapsed as soon as the start/stop button is pressed. When the start/stop button is pressed again. It stops and indicates the time interval recordes by it. A reset button restores its initial zero setting.
