Hello friends, In this video we will discuss
about least count... we will cover here- definition and equation of least count, how to find out
least count of ruler, protractor, stopwatch and Vernier caliper.. what is the least count of a measuring device?.. the smallest value that can be measured by
the measuring instrument is called as least count.. in this ruler this is a centimeter
scale and we can measure the smallest length.. this much.. so the value of the smallest division is called
as least count. so how to find out the value of this smallest
division. We use the formula, scale reading divided
by number of divisions. So suppose for this centimeter scale, from
zero to 1, scale reading is 1 centimeter and this scale reading is divided into- 123456789
10 divisions. 1 Centimeter is divided into 10 division..so
we got 1 centimeter divided by 10 that equals 0.1 cm. So 0.1 cm is the least count of this centimeter
scale.. On the other side there is a inch scale also.. Let's find out the least count of this inch
scale. so we have to figure out the length of this
smallest division. this length. so for that we will take a bigger reading
like from zero to 1 inch. this one is is divided into 12345678 , 8 divisions. 1 inch is divided into 8 divisions that it
equals 0.125 inch. so this is the least count of this inch scale. let's do the same thing for another example
like here is a protractor and we have to figure out the least count of this protractor. Means this length. For that let's take a bigger reading. like from zero to 10 so 10 degree is divided
into 12345678 910, 10 divisions. So 10 degree divided by 10 that equals 1 degree. So 1 degree is least count of this protractor. Same way We can find out the least count of
this stopwatch. So for this, this is zero and its 5.. so from
here to here, it's 5 seconds is divided into 5 divisions that equals 5 / 5 that is one
second. so one second is the value of 1 division or
1 second is the least count of this stopwatch. Let's take Vernier calipers. Vernier caliper was invented in 1631 by French
mathematician ’Pierre Vernier’. this device is used to measure internal and external diameter
of several objects. vernier calipers has two scales. first scale is, you can see, this longer scale. this is called as main scale and another is
this one from here to here. this is a small scale and this scale is called
as vernier scale so formula to find out least count of vernier caliper is - least count
of main scale divided by number of divisions on vernier scale. so just keep in mind there are 2 scales, first
is main scale and second is vernier scale so first we have to find out least count of
main scale that’s this centimeter scale. here it is written cm so it’s centimeter
scale. from zero to one it is 1 centimeter, scale
reading and this scale reading is divided into 10 divisions so we got 0.1 centimeter
which is the least count of main scale so we just plug in the value of 0.1 cm as least
count of main scale. it’s divided by number of divisions on vernier
scale. There are 20 divisions on vernier scale, so
divided by 20. This will give you 0.005 centimeter. this is the least count of vernier calipers. you can convert this value into millimeter
also. you know 1 cm= 10 millimeter, so you need
to multiply this value by 10. So this will become 0.05 mm. I hope you understand least count now if you
have any questions, please ask your questions in the comment box given below. thank you!