# Physics isa Help

WatchPage 1 of 1

Go to first unread

Skip to page:

can someone help me with this isa question I do half of it and cant do and understand how the second half is done. The question is

A student doing a similar experiment measures the diameter of the bore of the syringe to be 12.2 ±0.1mm and the unloaded length L to be 55±2mm.

Use these results to calculate the volume of the air in the unloaded syringe and the uncertainty in this volume. (Given that V = πr2h from the physics data sheet).

A student doing a similar experiment measures the diameter of the bore of the syringe to be 12.2 ±0.1mm and the unloaded length L to be 55±2mm.

Use these results to calculate the volume of the air in the unloaded syringe and the uncertainty in this volume. (Given that V = πr2h from the physics data sheet).

0

reply

Report

#2

Uncertainty is combined by

In your formula for volume the quantities are multiplied so add the % uncertainties in

As

This is a standard procedure in practical physics.

*adding the*in the two quantities when they are multiplied or divided in a formula.**%**uncertaintiesIn your formula for volume the quantities are multiplied so add the % uncertainties in

**r**and h to get the % uncertainty in V.As

**r**is squared you need to double its % uncertainty.This is a standard procedure in practical physics.

0

reply

Report

#3

Why would you use absolute uncertainty? Is there any specific explanation or any justification to use absolute uncertainty?

0

reply

Report

#4

(Original post by

Why would you use absolute uncertainty? Is there any specific explanation or any justification to use absolute uncertainty?

**thestudent_09**)Why would you use absolute uncertainty? Is there any specific explanation or any justification to use absolute uncertainty?

This is the rule.

When adding or subtracting values, add the absolute uncertainties.

When multiplying or dividing values, add the % uncertainties.

0

reply

Report

#5

(Original post by

Yes, when you add or subtract two values, each with an absolute uncertainty, you add the absolute uncertainties to get the total uncertainty.

This is the rule.

When adding or subtracting values, add the absolute uncertainties.

When multiplying or dividing values, add the % uncertainties.

**Stonebridge**)Yes, when you add or subtract two values, each with an absolute uncertainty, you add the absolute uncertainties to get the total uncertainty.

This is the rule.

When adding or subtracting values, add the absolute uncertainties.

When multiplying or dividing values, add the % uncertainties.

0

reply

Report

#8

(Original post by

What about the uncertainty where you calculate the range of measurements and divide by 2? Is there a specific reason why you would use this uncertainty?

**thestudent_09**)What about the uncertainty where you calculate the range of measurements and divide by 2? Is there a specific reason why you would use this uncertainty?

0

reply

Report

#9

(Original post by

Are you asking why uncertainty is used in practical physics?

**Stonebridge**)Are you asking why uncertainty is used in practical physics?

0

reply

(Original post by

Uncertainty is combined by

In your formula for volume the quantities are multiplied so add the % uncertainties in

As

This is a standard procedure in practical physics.

**Stonebridge**)Uncertainty is combined by

*adding the*in the two quantities when they are multiplied or divided in a formula.**%**uncertaintiesIn your formula for volume the quantities are multiplied so add the % uncertainties in

**r**and h to get the % uncertainty in V.As

**r**is squared you need to double its % uncertainty.This is a standard procedure in practical physics.

0

reply

Report

#11

Rearrange the formula for k (which you did in the previous part) and find its value.

On the other side of the formula you have T², m, x and L either multiplied or divided.

So the % uncertainty in k is the sum of the % uncertainties in m, x, and L plus

On the other side of the formula you have T², m, x and L either multiplied or divided.

So the % uncertainty in k is the sum of the % uncertainties in m, x, and L plus

**2 times**the % uncertainty in T (as it's T²).
0

reply

(Original post by

Rearrange the formula for k (which you did in the previous part) and find its value.

On the other side of the formula you have T², m, x and L either multiplied or divided.

So the % uncertainty in k is the sum of the % uncertainties in m, x, and L plus

**Stonebridge**)Rearrange the formula for k (which you did in the previous part) and find its value.

On the other side of the formula you have T², m, x and L either multiplied or divided.

So the % uncertainty in k is the sum of the % uncertainties in m, x, and L plus

**2 times**the % uncertainty in T (as it's T²).yes i did that and got the percentage uncertainty to be 5.1% but it isnt asking for the percentage uncertainty but for the uncertainty of the constant which is apparently 2 i dont know how they got to that.

0

reply

Report

#13

(Original post by

Thanks so much for replying

yes i did that and got the percentage uncertainty to be 5.1% but it isnt asking for the percentage uncertainty but for the uncertainty of the constant which is apparently 2 i dont know how they got to that.

**mohamedksmaar**)Thanks so much for replying

yes i did that and got the percentage uncertainty to be 5.1% but it isnt asking for the percentage uncertainty but for the uncertainty of the constant which is apparently 2 i dont know how they got to that.

If I had a value of, say, 200 and it was ± 5% then I would find 5% of 200, which is 10, and then say the value is

200 ±10

0

reply

(Original post by

Well what is 5% of that value?

If I had a value of, say, 200 and it was ± 5% then I would find 5% of 200, which is 10, and then say the value is

200 ±10

**Stonebridge**)Well what is 5% of that value?

If I had a value of, say, 200 and it was ± 5% then I would find 5% of 200, which is 10, and then say the value is

200 ±10

0

reply

Report

#15

(Original post by

Yes but I dont already have that value im asked to work it out . The question wants the uncertainty of k but I go up to working out the perentage uncertainty and then dont know how to convert it. Thanks

**mohamedksmaar**)Yes but I dont already have that value im asked to work it out . The question wants the uncertainty of k but I go up to working out the perentage uncertainty and then dont know how to convert it. Thanks

I assumed you had done 3d which involves actually calculating the value of k.

Just rearrange the formula and plug in the values you have been given to find k.

Then do what I said in my last post to find the absolute uncertainty from the % uncertainty.

Either that or I really don't get what it is you are asking.

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top