Mass
Measuring Instruments:
A Beam Balance:
In a beam
balance, the unknown mass is placed in one pan. It is balanced by putting known
masses in the other pan.
Physical Balance:
A
physical balance is used in the laboratory to measure the mass of various
objects by comparison.
Lever Balance:
A
lever balance consists of a system of levers. When lever is lifted placing the
object in one pan and standard masses on the other pan, the pointer of the
lever system moves. The pointer is brought to zero by varying standard masses.
Electronic Balance:
Electronic
balance come in various ranges: milligram ranges, gram ranges and kilogram
ranges. Before measuring the mass of a body, it is switched on and its reading
is set to zero. Then place the object to be weighted. The reading on the
balance gives you the mass of the body placed over it.
Difference between Balances:
Beam
Balance
|
Physical
Balance
|
Electronic
Balance
|
A
sensitive beam balance may be able to detect a change as small as of 0.1 g or
100 mg
|
Least
count of the physical balance may be as small as 0.01g or 10mg. Therefore its
measurement would be more precise than a sensitive beam balance.
|
Last
count of an electronic balance is 0.001g or 1mg. Therefore its measurement
would be more precise than a sensitive physical balance. Thus electronic
balance is the most sensitive balance.
|
Stop Watch:
A stop watch is
used to measure the time interval of an event. There are tow types of stop
watches.
·
Mechanical Stopwatch
·
Digital Stopwatch
Mechanical Stopwatch:
A
mechanical stopwatch can measure a time interval up to a minimum 0.1 second.
Digital Stopwatch:
Digital
stopwatch is commonly used in laboratories. It can measure a time interval as
small as 
second or 0.01 second.
second or 0.01 second.
How to use a stopwatch?
A mechanical stopwatch has a knob
that is used to wind the spring. The watch starts when the knob is pressed
once. When pressed second time it stops the watch while the third press brings
the needle back to zero position.
In digital stopwatch there are two
buttons Start/Stop and reset button. To indicate the time lap, the start/stop
button is pressed. As soon as start/stop button is pressed again, it stops. A
reset button restores its initial zero setting.
Measuring Cylinder:
A
measuring cylinder is a glass or transparent plastic cylinder. It has a scale
along its length that indicates the volume in milliliter (mL). Measuring
cylinder has different capacities from 100 mL to 2500 mL. They are used to
measure the volume of a liquid or powdered substance. It is also used to find
the volume of an irregular shaped solid insoluble in a liquid by displacement
method.
Significant Figures:
The significant figures are all the
accurately known digits and the first doubtful digit.
Rules to identify the significant figure:
1.
Non-Zero digits are always
significant.
2.
Zeros between two
significant figures are also significant.
3.
Zero or ending zeros on the
right in decimal fraction are significant.
4.
Zeros written on the left
of the decimal point for the purpose of spacing the decimal point are not
significant.
5.
In whole numbers that end in
one or more zeros without a decimal point, the zeros may or may not be
significant.
Get a test for Ch# 1
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