# Some of the answers (1 Viewer)

#### lolcakes52

##### Member
I wrote these myself from what I could remember of the exam and by the answers on the forum. I got bored so I might do some more later. If people could post exam questions that would be great.

Here it is

#### NickGero

##### Member
Your Question 8 is wrong. You have to use trig ratios to calculate the length of the wire. So 0.2m is certainly not the length. It's A.

#### lolcakes52

##### Member
Your Question 8 is wrong. You have to use trig ratios to calculate the length of the wire. So 0.2m is certainly not the length. It's A.
Read the bit after the multiple choice about number 8. I explain the working out. How would you approach the question if the length of the wire was 0.2?

#### NickGero

##### Member
Read the bit after the multiple choice about number 8. I explain the working out. How would you approach the question if the length of the wire was 0.2?
No your approach for calculating F = BIlsin(theta) is correct. But 0.2 is the height of the field. The length of the wire in the field is calculated as follows:

sin30 = 0.2/length
Length = 0.2 /sin30
= 0.4

Therefore:

0.03 = 0.05 x I x 0.04 x 1
I = 1.5A

#### lolcakes52

##### Member
The question was actually in my trial and I did the same calculation as you and picked the wrong multiple choice.

#### steero1

##### New Member
After reading your pendulum i kinda got sick no offence but it was soo terrible. What school do you go to?

1st of all reliability is not increased by dividing by 10 oscillations that would reduce errors and hence increase accuracy.
2nd of all reliability of results would be to plot a line of best fit and see if outliers exist and hence removing them.

#### someth1ng

##### Retired Nov '14
After reading your pendulum i kinda got sick no offence but it was soo terrible. What school do you go to?

1st of all reliability is not increased by dividing by 10 oscillations that would reduce errors and hence increase accuracy.
2nd of all reliability of results would be to plot a line of best fit and see if outliers exist and hence removing them.
I did that AND said that the experiment should be repeated...lol and to assess the reliability, I said to refer to the consistency of results. If results are consistent, it is reliable.

#### D94

##### New Member
I did that AND said that the experiment should be repeated...lol and to assess the reliability, I said to refer to the consistency of results. If results are consistent, it is reliable.
That's only half of the answer. Consistent results does not necessarily mean they are reliable. You could have some fundamental error in your experiment, but it may still yield consistent results, so these results cannot be trusted. Reliability looks are how trustworthy the results and the whole experiment are. One test would be to ensure the experiment was set up according to correct standards and all equipment used were precise for the experiment. After saying that, you can then talk about consistency, repeating results, etc.

#### someth1ng

##### Retired Nov '14
That's only half of the answer. Consistent results does not necessarily mean they are reliable. You could have some fundamental error in your experiment, but it may still yield consistent results, so these results cannot be trusted. Reliability looks are how trustworthy the results and the whole experiment are. One test would be to ensure the experiment was set up according to correct standards and all equipment used were precise for the experiment. After saying that, you can then talk about consistency, repeating results, etc.
Isn't that a problem with validity? If you have an error in your experiment, the experiment is invalid.

Also, this was a 1 mark question.

#### mickstarify

##### Member
No your approach for calculating F = BIlsin(theta) is correct. But 0.2 is the height of the field. The length of the wire in the field is calculated as follows:

sin30 = 0.2/length
Length = 0.2 /sin30
= 0.4

Therefore:

0.03 = 0.05 x I x 0.04 x 1
I = 1.5A
+1, OP your 8 is wrong its A

#### D94

##### New Member
Isn't that a problem with validity? If you have an error in your experiment, the experiment is invalid.

Also, this was a 1 mark question.
Similar, I would never just say "consistent results", full stop. Considering it was worth 1 mark, then you'll be fine with that answer.

Reliability is how trustworthy an experiment is. If you used a ruler which had undergone deformation and it was longer than normal, and you used this to determine your results, the whole experiment is still valid (as in, your methodology and logic is correct), but your equipment used is not reliable. Your results will still be similar and consistent, but your results cannot be trusted because of this fundamental error.

There will always be errors in experiments. That is why results are never completely reliable. But do we say the experiment is invalid? No.

#### lolcakes52

##### Member
After reading your pendulum i kinda got sick no offence but it was soo terrible. What school do you go to?

1st of all reliability is not increased by dividing by 10 oscillations that would reduce errors and hence increase accuracy.
2nd of all reliability of results would be to plot a line of best fit and see if outliers exist and hence removing them.
Reliability is about getting results in a small range, isn't it? By removing errors we are removing the size of outliers... Accuracy is how correct the answer is. So we could have ten oscillations but our method could be flawed so accuracy isn't increased. But by minimising the size of errors we could get more consistant and reliable results, because the error from one measurement is not as significant so the errors from all measurements would not be as significant.

It wasn't reliability of results, it was reliability of data collected. So the changes must be to the method, not to the results.

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#### kingkong123

##### Member
Similar, I would never just say "consistent results", full stop. Considering it was worth 1 mark, then you'll be fine with that answer.

Reliability is how trustworthy an experiment is. If you used a ruler which had undergone deformation and it was longer than normal, and you used this to determine your results, the whole experiment is still valid (as in, your methodology and logic is correct), but your equipment used is not reliable. Your results will still be similar and consistent, but your results cannot be trusted because of this fundamental error.

There will always be errors in experiments. That is why results are never completely reliable. But do we say the experiment is invalid? No.
I don't think this is completely correct. Reliability is indeed a measure of how consistent the results are - even if they are incorrect. Take an archery shooter as an example. Consider someone who never hits the bulls eye, but they consistently shot the number 9, they are a reliable shooter (despite not getting the bullseye). Some one who hits the bulls eye every now and then is considered an accurate shooter, but someone who can consistently hit the bulls eye is considered both RELIABLE AND ACCURATE. Your example about the deformed ruler is deemed INACCURATE, not unreliable.

http://en.wikibooks.org/wiki/A-level_Physics/Forces,_Fields_and_Energy/Electromagnetism

L is the value of the length of wire, not the length of wire perpendicular to the field. The inclusion of the sin(theta) remedies this by finding the length of the wire perpendicular to the field. They give you the value of the wire perpendicular to the field straight away.
You need to find the length of the wire that is in the field, you do this by using trigonometry. The length of the wire is perpendicular to the field in the position it is in (despite being at the 30 degree slant), so you don't use the 0.2m length they gave you. The answer is A 1.5A

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#### someth1ng

##### Retired Nov '14
I don't think this is completely correct. Reliability is indeed a measure of how consistent the results are - even if they are incorrect. Take an archery shooter as an example. Consider someone who never hits the bulls eye, but they consistently shot the number 9, they are a reliable shooter (despite not getting the bullseye). Some one who hits the bulls eye every now and then is considered an accurate shooter, but someone who can consistently hit the bulls eye is considered both RELIABLE AND ACCURATE. Your example about the deformed ruler is deemed INACCURATE, not unreliable.
D94 is definitely not WRONG but the definition of reliability/validity/accuracy seems to vary quite a bit, especially between different fields.

#### kingkong123

##### Member
D94 is definitely not WRONG but the definition of reliability/validity/accuracy seems to vary quite a bit, especially between different fields.
No, I agree, I never said he was WRONG, I said it is not completely correct. I agree with his comment that an experiment that achieves consistent results which are not completely valid (due to wrong experimental method, etc.) is not completely reliable, but for the scope of the HSC I think reliability is defined as the ability to achieve consistent results, whether or not the method is valid.

#### D94

##### New Member
I don't think this is completely correct. Reliability is indeed a measure of how consistent the results are - even if they are incorrect. Take an archery shooter as an example. Consider someone who never hits the bulls eye, but they consistently shot the number 9, they are a reliable shooter (despite not getting the bullseye). Some one who hits the bulls eye every now and then is considered an accurate shooter, but someone who can consistently hit the bulls eye is considered both RELIABLE AND ACCURATE. Your example about the deformed ruler is deemed INACCURATE, not unreliable.
Your analogy isn't really clear and not the best to compare with my example. A deformed ruler can yield consistent results, so by your definition, it is reliable(?). Sure, reliability is about consistency, however, it must also be trustworthy results (well, they are synonyms of each other). A ruler which is deformed is not trustworthy for this experiment within the reasonable error bounds, hence the results, whilst consistent, are not reliable. Can you really trust results which use a deformed ruler? No. You raised the point about accuracy, but all experiments are not 100% accurate; inaccuracy and unreliability are not mutually exclusive.

Anyway, there's no point debating this if it's coming down to how we define the word - Look, I could be completely wrong and completely off the mark, but I've written what I said numerous times in many reports both scientific and historical. It hasn't been raised, so there's no reason to alter my definition.

#### mickstarify

##### Member
http://en.wikibooks.org/wiki/A-level_Physics/Forces,_Fields_and_Energy/Electromagnetism

L is the value of the length of wire, not the length of wire perpendicular to the field. The inclusion of the sin(theta) remedies this by finding the length of the wire perpendicular to the field. They give you the value of the wire perpendicular to the field straight away.
Do you have a copy of the exam? look at the diagram, it clearly shows 0.2m is the perpendicular height of the wire. F=BILsin(theta), L is the full length of the conductor in the field, as such we need to use the sin30 & our perpendicular height to find the full length of the wire which is 0.2/sin30 or 0.4.

#### uart

##### Member
$\bg_white B I L \sin \theta_1$

$\bg_white L = L_{perp}/\sin \theta_2$

OP (lolcakes) has fallen for a classic trap here in assuming that "theta1" is equal to "theta2" and hence the sin(theta) terms cancel out.

In fact theta2 = 30 degrees while theta1 (the angle between the current and the B field) is 90 degrees. So sorry OP but you got Q8 wrong.

#### brianphamm

##### Member
Your analogy isn't really clear and not the best to compare with my example. A deformed ruler can yield consistent results, so by your definition, it is reliable(?). Sure, reliability is about consistency, however, it must also be trustworthy results (well, they are synonyms of each other). A ruler which is deformed is not trustworthy for this experiment within the reasonable error bounds, hence the results, whilst consistent, are not reliable. Can you really trust results which use a deformed ruler? No. You raised the point about accuracy, but all experiments are not 100% accurate; inaccuracy and unreliability are not mutually exclusive.

Anyway, there's no point debating this if it's coming down to how we define the word - Look, I could be completely wrong and completely off the mark, but I've written what I said numerous times in many reports both scientific and historical. It hasn't been raised, so there's no reason to alter my definition.
Reliability in high school terms, is the consistency of the results. No matter how it was performed, valid or invalid, if the results are consistent, it is reliable. By saying whether to trust it or not comes under validity. An experiment may be reliable but not valid. What someth1ng wrote is correct and should get the mark.