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Edexcel_IAS_Physics_WPH13_Revision_Notes
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- PHYSICS
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- PEARSON (PEARSON)
Edexcel_IAS_Physics_WPH13_Revision_Notes
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REVISION GUIDEPearson
Edexcel
IAS
PHYSICS
WPH13
,Q: How can we measure small length by using vernier calipers?
Vernier callipars is used to measure the length of 5 cm to 15 cm. It has 2 scales: main scale and vernier
scale. We can measure the diameter of an object keeping it in between the 2 jaws.
diameter = main scale reading + vernier scale reading
= main scale reading + vernier coincidence × vernier constant
Q: What is vernier coincidence?
When the object is in between the 2 jaws, a line of vernier scale coincides with one line of the main
scale. This line of the vernier scale gives the vernier coincidence.
Q: What is vernier constant?
The minimum length we can measure by vernier calipers is called vernier constant.
smallest one division of main scale
vernier constant =
total number of division in the vernier scale
𝑠
𝑉𝐶 =
𝑛
Q: How can we get main scale reading?
Keeping the object in between the jaws, the zero line of the vernier scale causes one line of the main
scale. This line gives the main scale reading.
Q: How can we measure a small length by using a micrometer screw gauge?
It can measure the length of several centimeters. It has also 2 scales: main scale and thimble scale. We
should keep the object in between the sleeve and spindle. We can measure the length by using the
formula
diameter = main scale reading + thimble scale coincidence × least count
Q: 0 error of micrometer screw gauge.
When the sleeve and spindle are touching each other and if the detum line of line scale doesn’t coincide
with 0 line of the circular scale, then the error is called 0 error.
, zero error = how many no. of division below or above the detum line is the zero line × least count
diameter = total reading − (±e)
Uncertainty
Q: What is uncertainty?
The uncertainty is an actual range of values around a measurement, within which we expect the true
value to lie. The uncertainty is an actual number with an unit.
An error is just a problem which causes the reading to be different from the true value. Although a zero
error can have an actual value. For example, if we happen to know that the true value of a length is 21.0
cm and an error or problem causes the actual reading to be 21.5 cm, then, since the true value is 0.5 cm
away from the measurement, the uncertainty is ±0.5 cm.
The uncertainty can be estimated in two ways:
1. Using the scale division on the scale.
2. Repeating the readings.
There are two types of uncertainty
1. Instrumental uncertainty: uncertainty of measured value.
2. Absolute uncertainty: uncertainty of any calculated value.
Q: How can we calculate the uncertainty?
Let the true length of a bar, 𝑙 = 4.6cm
the measured length, 𝑙𝑚 = 4.7cm
Instrumental ∆ of this measured value
= (4.7 – 4.6 ) = 0.1 cm
𝑙 = (4.7 ± 0.1) cm
∆
%∆ = × 100%
measured value
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