Conversation started Apr 4, 2019 at 14:40.
Abcd
Abcd
Apr 4, 2019 14:40
36 mins ago, by Abcd
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@JohnRennie C2
John Rennie
John Rennie
@Abcd for C2 the readings match at 36mm on the main scale. Yes?
@Abcd hello?
Abcd
Abcd
@JohnRennie back 1 sec
@JohnRennie yes, then?
John Rennie
John Rennie
@Abcd and the match on the vernier scale is at 7. So the distance from zero to the match on the vernier scale is 7 times the vernier spacing i.e. 7.7 mm.
Abcd
Abcd
@JohnRennie K?
John Rennie
John Rennie
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Abcd
Abcd
Apr 4, 2019 14:53
@JohnRennie Ok, then?
John Rennie
John Rennie
So the reading on the main scale is 36 - 7.7 = 28.3 mm
Abcd
Abcd
13 mins ago, by John Rennie
@Abcd for C2 the readings match at 36mm on the main scale. Yes?
@JohnRennie But for MSR we take the one before 0 of VS right??
which is 28 in this case
John Rennie
John Rennie
The reading on the main scale is where the left red line is. So it's greater than 28 and less then 29, but we can't read exactly what it is.
But we know that 36 on the main scale matches up with 7 on the vernier scale.
So if we start at 36 on the main scale and move left by 7 divisions on the vernier scale we will have reached the reading.
Abcd
Abcd
@JohnRennie In 12.7 question also the 0 didnt coincide
John Rennie
John Rennie
@Abcd to be honest I wish I'd just drawn a diagram like the one above for that question.
Isn't it obvious from the diagram why the reading is 28.3? No messing around with MSDs or whatever.
Abcd
Abcd
Apr 4, 2019 15:03
nope its not obvious to me
@JohnRennie why move left??
John Rennie
John Rennie
@Abcd If you start with the calipers closed then the zero on the main scale and the zero on the vernier scale are aligned. Yes?
Abcd
Abcd
@JohnRennie yes
John Rennie
John Rennie
Now you put some object with a size $D$ in the jaws. That means the movable jaw has to move a distance $D$ to the right.
The vernier scale is written on the movable jaw, so that means the whole vernier scale moves a distance $D$ to the right along with the movable jaw.
OK so far?
Abcd
Abcd
@JohnRennie yeah
John Rennie
John Rennie
So the zero on the vernier scale is now at a distance $D$ on the main scale.
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Abcd
Abcd
Apr 4, 2019 15:10
@JohnRennie agree
John Rennie
John Rennie
We can see that $D > 28$ and $D < 29$ but we can't be any more precise than that because the main scale is only marked in 1 mm steps.
But we know that 7 on the vernier scale lines up with 36 on the main scale.
Abcd
Abcd
@JohnRennie ya
John Rennie
John Rennie
And we know the vernier spacing is 1.1mm
So that means $D + 7.7 = 36$
Abcd
Abcd
@JohnRennie Wow!!
 
Conversation ended Apr 4, 2019 at 15:14.