Teaching Ustad: Chapter 2 Physics Theory SSC Hyd Board

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Friday, October 16, 2020

Measuring cylinder

Ø It is made-up of glass.

Ø A scale in cubic centimeter or millimeter printed on it.

Ø It is used to find volume of liquids.

Ø When we pour liquids into the cylinder, the level of liquids in the cylinder in noted.

Ø We should keep the eye in level with the bottom of the meniscus of the liquid in order to read the volume correctly.

The liquid surface and the cylinder must be on the a horizontal table.

STOP WATCH

Ø We use a stopwatch for measurement of time, on our laboratories.

Ø It has two hands M and S,

Ø ‘M’ is for minutes and ‘S’ coincide with position of zero.

Ø The button ‘B’ is pressed and released for recording the time interval between the starts and stop of the event.

Ø By pressing and releasing button, the needle of stopwatch returned at zero and ready for next fresh reading.

MICRO METER SCREW GAUGE

Ø It has two scales, one is called main scale and other is called circular scale.

Ø It is used to measure the diameter and thickness of small objects.

Ø Spindle is an important part in screw gauge.

Ø To protect the screwed portion it kept into enclosed cylinder.

Ø Spindle moves through 0.5 mm or 0.05 cm for complete rotation. The distance is called pitch of the crew gauge.

Ø The circular scale moves on main scale, which is in millimeter.

When the object is being measure we rotate circular scale clockwise. Till spindle just touches the object. Now we may take reading.

A meter stick is graduate in millimeters hence it can measure a distance up to 1mm. to measure distance smaller than this other instruments are used vernier caliper is one of such instruments that can be used to measure a distance upto 0.05mm.

A vernier caliper consists off a rectangular steel bar whose one side is graduated in millimeters. This scale is known as main scale (MS). A small scale usually consisting of 10 division which slides over the main scale is known as vernier scale (VS).

This instrument has tow jaws called calipers which shown enables it to measure the internal as well as as the external diameter of a cylindrical project. A relatively this flat rod is attached to the sliding scale on back which enable it to measure the inner depth of the hollow cylinder.

SIGNIFICANT FIGURES, RULES OF SIGNIFICANT FIGURES

SIGNIFICANT FIGURES

In measurement the accurately known digits and first doubtful digits are called significant figures.

RULES OF SIGNIFICANT FIGURES:

Ø All non zero digits are significant figures.

e.g. 7686 has four significant figures.

Ø Zeros lying between the non-zeros are significant.

e.g. 304005 has six significant figures.

Ø All the zeros which locate the decimal point in a number less than one are not significant.

e.g. 0.0008765 has four significant figures.

Ø The zeros which are located immediately to the right of the decimal point are significant.

e.g. 38.0000 has six significant figures.

Ø Zeros lying the decimal point in a number greater than one are not necessarily significant.

e.g. 600 has only significant figure.

When two are more numbers are used in a calculation, the number of significant figures with answers in limited by the number of significant figures in the original data.

UNIT OF CONVERSION

UNIT CONVERSION

UNIT OF LENGTH	UNIT OF MASS	UNIT OF TIME
1 km = 1000 = 10³ m	1kg = 1000 = 10³ g (grams)	1h = 60 min
1m = 10 dm (decimeter)	1kg = 1000000=10⁶ mg (milligrams)	1 mint = 60 sec
1m = 100 = 10² cm	1 kg = 1000000000 = 10⁹ µg	1h = 60×60=3600 sec
1m = 1000 = 10³ mm		1sec = 1000 = 10³ ms
1m = 1000000 = 10⁶ µm		1s = 1000000 = 10⁶ µs
1m = 1000000000 = 10⁹ nm		1s = 1000000000 = 10⁹ ns

System of units, C.G.S SYSTEM, BRITISH ENGINEERING OR F.P.S SYSTEM, M.K.S SYSTEM, SYSTEM INTERNATIONAL (S.I SYSTEM)

System of units
The set of fundamental and derived units is called a system of units.

There are four types of system of nits.

C.G.S SYSTEM

In this system the three fundamental quantities length, mass and time’s units are taken as centimeter, gram and second. In this system the force is derived quantity and its is which is called dyne.

No.	Fundamental Quantity	UNIT	SYMBOL
1	Length	centimeter	cm
2	Mass	gram	g
3	Time	second	s

BRITISH ENGINEERING OR F.P.S SYSTEM
In F.P.S the length mass and time are fundamental quantities and their units are foot, pound and second respectively.

No.	Fundamental Quantity	UNIT	SYMBOL
1	Length	foot	ft
2	Mass	pound	lb
3	Time	second	s

M.K.S SYSTEM

In M.K.S the length mass and time are fundamental quantities and their units are meter, kilogram and second respectively. In this system the force is derived quantities and its unit is is called newton.

No.	Fundamental Quantity	UNIT	SYMBOL
1	Length	meter	m
2	Mass	kilogram	kg
3	Time	second	S

SYSTEM INTERNATIONAL (S.I SYSTEM)

In S.I system seven quantities are taken as fundamental quantities which are also called base

quantities. Their units are called fundamental units or base units or S.I units.

These quantities are Length, mass, time, electric current, temperature, luminous intensity, amount of substances.

S.I system of units are convenient for scientific work and it is an easy way for calculation.

There are seven Physical Quantities

No.	Fundamental Quantity	UNIT	SYMBOL
1	Length	meter	m
2	Mass	kilogram	kg
3	Time	second	s
4	Amount of substance	mole	mol
5	Thermodynamic Temperature	kelvin	K
6	Electric current	ampere	A
7	Luminous intensity	candela	Cd