Measurement
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Length is a physical quantity but meter is its unit
Standard units were developed to overcome variations with traditional units
Kilogram is the example of a unit
While measuring a horizontal length the position of our eye should be vertical
A unit is used to compare physical quantities of the same kind.
Edges of the scales should not be used to measure because the markings might be erased due to
constant usage or the edges would be broken.
Ampere is the SI unit of electric current and A is its symbol
If the unit of a physical quantity is derived from the name of a person it is written in lower case
Give an example - kelvin
CGS system was developed to measure smaller quantities
24 hours = 1 mean solar day = 86,400 seconds
Time interval is the time passed between two events
Multiples of physical quantities are factors used to create larger units Give an example - kilo
Submultiples of physical quantities are factors used to create smaller units Submultiples of kg is
gram
1 decimeter = 10 centimeters
1 meter = 10 decimeters
If the symbol of a physical quantity is derived from the name of a person it is written in upper
case . Give an example – K for kelvin
If the unit and symbol is not derived from the name of a person it is written in lower case. Give
an example - kilogram
1 hectometer = 10 decameters
The smallest sub multiple of the physical quantity of length is millimeter
Parallax error occurs due to wrong positioning of the eye while reading measurments
One of the precautions necessary while measuring lengths is that the scale should be placed
parallel to the length you are measuring.
Traditional units are not accurate and accepted by the majority of people
In the physical quantity of 5kgs, 5 is the number (magnitude) and kgs is the quantity
In a cube all sides are equal
A Cuboid is made up of rectangles
The volume of a cube is side *side* side
The SI unit of volume is m3
It is difficult to measure the volume of an irregular solid because there is no specific formula
SI unit of mass is kilogram
Physical balance is used to measure the weight of a platinum hook.
Beam balance is used to measure the weight of plastic packets
32. A shop that manufactures tiny high precision spare parts for vehicles will use a physical balance
because it needs to measure accurately.
33. 1 kilometer = 10 hectometers
34. 10 meters = 1 Decameter
35. The volume of a Cuboid is length *breadth * height
36. The length of a rubber is measured in millimeters but the length of a paper is measured in
centimeters
37. SI system consists of 7 base or fundamental quantities
38. Instruments used for measuring mass are physical and beam balances
39. The smallest sub multiple of the physical quantity of mass is milligram
40. A measuring cylinder is used for measuring volume of a liquid
41. A housewife calculated the volume of her vegetable cutting board. She will express her answer
in (units)3 (since it is three dimensional)
42. A bar tender calculated the volume of alcohol consumed by a customer. He will express the
answer in milliliter
43. The volume of a liquid is the capacity of the container in which it is stored.
44. The SI unit of time is seconds
45. Light year is the distance travelled by light in one year
46. The weight of a sharpener is measured in milligrams but the weight of a pile of books will be
measured in kilograms
II. State True or False - If false, correct the sentence and explain with an example if applicable
1. Plural form a symbol is written with s at the end – False
Correct Statement – Plural form of a symbol is written without s at the end.
Eg. 5 seconds is written as 5 s and not 5ss
2. A full stop is written at the end of a symbol of a physical quantity – False
Correct statement – A full stop is never written at the end of a symbol of a physical quantity
Eg – the correct way of writing 5 meter is 5m and NOT 5m.
3. 5 ms is correct way of writing 5 meters – False
Correct statement – 5 m is the correct way of writing 5 meters
This is because s should never be written at the end of symbols of physical quantity.
III. Answer the following
1. Ram was presented by a spinning top by his friends for his birthday. He decided to find the
length of this top for his Physics project. Which instrument will he use and why?
Answer : Ram will use a thread since the spinning top is an irregular object and the
length cannot be found using a scale
2. A man had a bought a piece of land as investment. Will he find the area of the land or volume of
the land and why? How will do so?
Answer : He will find the area as the land is has only two dimensions of length and
breadth. Volume is for 3 dimensional objects He will do so by using a specific formula
3. Rita plucked a flower from her garden. She wanted to find the area of her flower. How will she
find it and why?
Answer: Rita will use a graph paper to find out the area as it is an irregular object.
4. Somu was presented with a chess board when he came first in class. Then he was asked to find
out the volume of the chess board by his teacher. Was she correct or wrong? Give reasons for
your answer
Answer: The teacher was wrong as volume can be found only for 3 dimensional objects .
The chess board is a two dimensional object have dimensions of length and breadth
only.
5. A farmer got 10 quintals of grains from his farm. Express this as a multiple of mass.
Answer : 10 quintals = 1 metric ton.
So the farmer got 1 metric ton of grain from his farm
6. 1 quintal of rice was eaten by insects. Express this as a sub multiple of mass
Answer : 1 quintal = 100 kilograms
So 100 kilograms of rice was eaten by insects.
7. In a laboratory, a student places some ice in a beaker for melting on a Bunsen burner. He
wanted to know the exact time taken for the ice to melt. Which instrument will he used to do
so?
Answer: He will use a stop watch as it is used to measure time passed between two
event i.e ice starting to melt and ice completely melting.
IV. Give reasons why
1. All masses cannot be measured in quintals.
Answer : All masses cannot be measured in quintals as some objects have smaller mass.
Hence they need to be measured in grams or kilograms.
2. When we find the volume we always write (symbol of unit)3
Answer – Volume is found out for 3 dimensional objects i.e objects which have length,
breadth, height.
Also volume = Length * Breadth* height . So the unit is being multiplied thrice. Hence
the answer is expressed in (symbol of unit)3
3. SI system is preferred when compared to MKS and CGS system.
Answer – SI system is preferred because it has physical quantities of length, mass, time,
electric current, luminosity etc unlike MKS and CGS systems which consists of only basic
units of length, mass and time.
V. Find the odd one out and give reasons for your answer
1. light year, second, minute
Answer – Light year
This is because light year is used to measure distance but second and minute is used to measure
time.
2. 5kgs, 5KGS, 5kilograms
Answer – 5KGS
Since it is the wrong way of writing symbols. Symbols of units not derived from the
name of a person should be written in small letters
3. Safety pin, a cheese slice, watermelon, green chili
Answer – Water melon
This is because the others weight only a few grams where as a water melon will weigh a
few kilograms.
4. Centimeter, ampere, gram, second
Answer – Ampere
Since all others belong to the CGS system while ampere does not
5. Camera, shoe box, cupboard , table top
Answer – Table Top
This is because table top is a two dimensional object ( has only length and breadth)
while the others are three dimensional objects( have length, breadth, height).
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