jm1234567890
Premium Member
I sent an e-mail asking for this
John,
The rules for expressing the answer to a prelab question that requires a
quantity and an uncertainty are the same as those that normally apply to
experimental physics. The uncertainty in a quantity is always rounded off
to one significant figure. The corresponding quantity then must be
rounded off to the same decimal place that the uncertainty is rounded off
to. The reason is due to the fact that the uncertainty indicates the precision
to which an empirically determined quantity is accurate to. To express a
quantity to too few decimal places will give cause the determination of a
quantity to be less accurate than what it should be. To express a quantity
to too many decimal places will make the determination look more
accurate than what it is as the surplus decimal places cannot be known
with any certainty. Below are some examples:
1. A length of 0.4145 m with an uncertainty of 0.005 m would need to be
expressed as (0.415 0.005) m, or if using WebCT, it would be entered in
the format (0.415 +- 0.005) m.
2. A mass of 0.03240 kg with an uncertainty of 0.00001 kg would need to
be expressed as (0.03240 0.00001) kg, or if using WebCT, it would be
entered in the format (0.03240 +- 0.00001) kg. Note that the last zero
digit here is required, as the uncertainty requires that the quantity must be
expressed to five decimal places. This would mean that a quantity like a
length of 1.0000 m with an uncertainty of 0.0005 m must be written as
(1.0000 0.0005) m, and not (1 0.0005) m.
3. A pressure of 45361 Pa with an uncertainty of 300 Pa would be
expressed as (45000 300) Pa, or if using WebCT, (45000 +- 300) Pa.
Note that the quantity is still rounded off to the same precision as the
uncertainty, even though both are larger than one.
Regarding the correct usage of units when entering data into WebCT, it is
recommended that you follow those of the page on WebCT that outlines
the correct usage of units in Ralph and Prelabs. The rules used in this are
as follows:
1. Units that are to the power of 1 are expressed with no power. e.g. kg^1
is expressed just as kg.
2. Units that are to a positive power (other than 1) are expressed with the
use of the "^" character. e.g. cubic metres is expressed as m^3.
3. Units that have a negative power are expressed with the use of the "/"
character. e.g. metres per second is expressed as m/s, and not m s^-1.
4. If there is a mixture of different units, the units to a positive power are
always expressed before those with a negative power. e.g. the units of
density are kg/m^3 and not kgm^-3. The units of viscosity are Ns/m^2
and not Nsm^-2. The units of of specific heat are J/kg K, and not Jkg^-
1K^-1.
If you have any further questions about this, please come and see me. I am
in the prep room of the First Year Lab most days (41.263a).
Richard Baker.
John,
The rules for expressing the answer to a prelab question that requires a
quantity and an uncertainty are the same as those that normally apply to
experimental physics. The uncertainty in a quantity is always rounded off
to one significant figure. The corresponding quantity then must be
rounded off to the same decimal place that the uncertainty is rounded off
to. The reason is due to the fact that the uncertainty indicates the precision
to which an empirically determined quantity is accurate to. To express a
quantity to too few decimal places will give cause the determination of a
quantity to be less accurate than what it should be. To express a quantity
to too many decimal places will make the determination look more
accurate than what it is as the surplus decimal places cannot be known
with any certainty. Below are some examples:
1. A length of 0.4145 m with an uncertainty of 0.005 m would need to be
expressed as (0.415 0.005) m, or if using WebCT, it would be entered in
the format (0.415 +- 0.005) m.
2. A mass of 0.03240 kg with an uncertainty of 0.00001 kg would need to
be expressed as (0.03240 0.00001) kg, or if using WebCT, it would be
entered in the format (0.03240 +- 0.00001) kg. Note that the last zero
digit here is required, as the uncertainty requires that the quantity must be
expressed to five decimal places. This would mean that a quantity like a
length of 1.0000 m with an uncertainty of 0.0005 m must be written as
(1.0000 0.0005) m, and not (1 0.0005) m.
3. A pressure of 45361 Pa with an uncertainty of 300 Pa would be
expressed as (45000 300) Pa, or if using WebCT, (45000 +- 300) Pa.
Note that the quantity is still rounded off to the same precision as the
uncertainty, even though both are larger than one.
Regarding the correct usage of units when entering data into WebCT, it is
recommended that you follow those of the page on WebCT that outlines
the correct usage of units in Ralph and Prelabs. The rules used in this are
as follows:
1. Units that are to the power of 1 are expressed with no power. e.g. kg^1
is expressed just as kg.
2. Units that are to a positive power (other than 1) are expressed with the
use of the "^" character. e.g. cubic metres is expressed as m^3.
3. Units that have a negative power are expressed with the use of the "/"
character. e.g. metres per second is expressed as m/s, and not m s^-1.
4. If there is a mixture of different units, the units to a positive power are
always expressed before those with a negative power. e.g. the units of
density are kg/m^3 and not kgm^-3. The units of viscosity are Ns/m^2
and not Nsm^-2. The units of of specific heat are J/kg K, and not Jkg^-
1K^-1.
If you have any further questions about this, please come and see me. I am
in the prep room of the First Year Lab most days (41.263a).
Richard Baker.
Though there was the odd few i got 100% for 
