junior cert science

Junior Cert Science: Unusual demonstration of magnetic fields

This week we looked at a concept called ferromagnetism which allows us to demonstrate the 3-dimensional nature of magnetic fields.

Thanks to my first years for being so co-operative 🙂

Here’s another way of illustrating the idea (which we didn’t do)

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How to get an A in Junior Cert Science: Part 2 – the graphs

Since this science course was first examined in 2006 graph questions have become quite common.

There are different types of graph questions, and we will look at each of these different types in turn.

There is nothing scary here, and you have probably covered them all in maths anyway. It’s just that the science textbooks don’t seem to do a very good job of telling us why we have them in the first place, or why there are different types.

Why do we have graphs?

You won’t get asked this so you don’t have to learn it off by heart – I just thought you deserved to know.

There are many different reasons, but we’ll just look at two here.

Reason 1:

To see what the relationship is between two variables, e.g. between the extension of a string and the force which caused it.

Now assuming that a bigger force causes a bigger extension, the question is; are the two quantities directly proportional? i.e. if the size of the force doubles then the extension should be twice as much, if the force triples the extension will be three times as much etc.

Another way of saying this is that the two quantities increase at the same rate (as force is increased the extension increases at the same rate).

Or finally the scientific way of saying this is to say that the two quantities are directly proportional to each other (you must learn the phrase in italics off by heart because it gets asked a lot as you will see below).

To investigate this you would plot the results on a graph, and if the two quantities are directly proportional then you will find that if you draw a line through the points you will end up with a straight line through the origin (the origin is the (0,0) mark).

 

Reason 2:

In some graphs the slope of the line gives us some extra information (and you must know what this is).

There are only three graphs which fall into this category so make sure that you know each of them.

1. The slope of a distance-time graph corresponds to the speed (or velocity) of the moving object

2. The slope of a velocity-time graph corresponds to the acceleration  of the moving object

3. The slope of a voltage-current graph corresponds to the resistance of the resistor under investigation.

 

Note that for each of these graphs you will also get a straight line going through the origin, which verifies that the two quantities are directly proportional to each other.

 

Which brings us to our next problem – how do we calculate the slope of a line?

 

To calculate the slope of a line

Pick any two points (from the graph) and label one point (x1y1) and the second point (x2y2).

Make life easy for yourself by picking (0,0) as one of the points (assuming the line goes through the origin).

You must then use the formula:                                    

slope = (y2 – y1)/(x2 – x1)

Note that you can also find this formula on page 18 of the new log tables

Yo – Which axis is the y-axis?

Remember the yo-yo? It goes up and down right? Well so does the y axis (and it begins at zero) so y-zero = yo

Now that’s just freaky.

How to get an A in Junior Cert Science: Part 1 – the maths bits

Many students are turned off Physics because of the maths involved, yet you only need to be able to do ordinary level maths in order to answer all questions which will appear on the Junior Cert paper.

Some of these are in the new log-tables, but others are not so you should really try to remember all of them because it not always easy to identify the formula you need from the list in the log-tables. Practice looking for them in pages 51 – 56.

To encourage students not to give up on these questions I have put together a document which includes all the equations on the Junior Cert Science syllabus. There are (only) ten of them and by-in-large they are very straightforward. The document includes every maths question that was ever asked on a Higher Level or Ordinary Level paper from when the syllabus was first examined in 2006 up until 2010. It also contains solutions to all these questions.

If you’re looking for a top grade in June you really should ensure that you’re familiar with all of these.

You can download this document here.

There’s also a section on Units (we tend to be a little fanatical about these in Physics) and finally a list of practice questions.

If you’re using this as a teacher it should make a nice revision class or two – good luck with it!

Junior Cert Science – Graphs and the phrase ‘directly proportional’

Usually there is at least one graph to draw on the Junior Cert Science paper, and if it’s in the Physics section then chances are it will be a straight line graph (the main exception is Cooling Curves). There’s nothing on the syllabus (that I’m aware of) that states that students are expected to know the significance of a straight line graph. In fact here’s a piece of research for you – next time you’re in class ask your students why we’re expected to bother with graphs in the first place. My bet is that very few will be able to give a convincing answer.

One reason we ‘bother’ with graphs is to establish a relationship between two variables; to use the correct jargon we want to see if the variables are ‘directly proportional’ to each other. Now that term ‘directly proportional’ is very important. In means in effect that the two variables are increasing at the same rate. For example if you are on a bicycle travelling at a steady speed of 10 m/s, then for every second that you cycle you will have travelled 10 m (d’oh), and if you travel for twice as long you will cover twice as much ground. If you travel for four and a half times as long, you will cover four and a half times the distance.
So again, the time and the distance covered are increasing at the same rate – they are directly proportional to each other.

The graph is our way of verifying this – it turns out that when you plot all the given data and you end up with a straight line which passes through (0,0) then we can state that the two variables are directly proportional to each other.

So why am I telling you all this now?
Because in the exam you may be asked to draw a graph and then say what the relationship is between the two variables. And if you don’t use the phrase ‘directly proportional’ in your answer then you probably won’t get full marks.
Now as I mentioned I have never seen this phrase highlighted in a Junior Cert textbook so you may well have heard it here first.

Now to help you I have compiled all the graph questions that have ever been asked at Junior Cert into one word document. You can find it on the revision page of thephysicsteacher here (it’s no.3 – Graphs). It also contains all the solutions to the questions, plus a list of do’s and don’ts.

Make sure you check it out before going into the exam. And if you’re reading this as a teacher please remember when photocopying to copy back-to-back and reduce two pages onto one. In doing so you reduce the amount of pages by a factor of 4.

Good luck!

BOARDS.IE – An intriguing resource

boards.ie

boards.ie seems to win awards every year for its site. For me it merely highlights the fact that everybody seems to be communicating with each other except teachers – sure what would we have to talk about?

Well here’s an interesting nugget – from the comments below (pasted from the relevant boards.ie pages) it would appear that quite a few teachers are not sure what they are supposed to do with their students’ experiment copies, or how to fill in the green investigation booklets. Remember that if the students don’t tick the relevant experiments in their green booklets then they automatically forfeit 10%.

The site itself is also a very useful resource for getting student feedback on their various exams – these kids tend to have more honesty and intelligence than we (I?) give them credit for:

ok everyone, don’t forget your hardbacks tomorrow!

What you mean “hardback”?

Experiment copy? I nearly forgot! Thanks guys for reminding me

Dunno what he is on about, you don’t get marked on your hardback. Maybe he means just for study purposes?

I’m not sure..

You get marked on your mandatory experiment hardback

Think he means your experiment copy?? I think!

Exactly. DO NOT forget it. If they go to check yours, and you’ve ticked the boxes to say you’ve done it, and its not there, they count that as cheating.

nah you’re not supposed to take it in with you afaik…the supervisors would have reminded us anyways….

They inspect a small % of schools and the hbacks are sposed to be with your science teacher.
You’re meant to bring it in because every year they check a few schools, and if they check your school and they’re not there for inspection you lose your 10%

We’ve been told a million times to bring ’em in tomorrow

Our teacher collected ours at the end of April, she said there was a deadline I had to do about 15 experiments in the space of 3 days!

But the inspectors only come in the summer!
I’ve had to write up a good few today, but that was my own lazy selfs fault..

ive a few only not filled the science teacher said it was ok since half the class or more didnt get em finished either =P

I aint bringing mine in that’d be effort and no one told us to we were given them back and told it was fine?

Gawd im confused i ticked no boxes =S my science teacher is crap we have been reading out of a book all year and havent done any experimanens execpt for the 2 ones you did for 25%

My science teacher told us that we put them in a little pocket in this folder that also has our investigations in it. They just check to see whether you’re telling the truth or not. sure if yer teacher told u its fine then its not yer fault so theyd probably give you the marks

Exam done in 43 minutes. All spaces filled. No blanks. Two questions I couldn’t answer (one on chromosomes, one on the Hoffman Voltameter). Everything else is as far as I know it, correct. Junior Cert science in need of reform? hell yes
I know I’m probably not alone on this front.

have to agree ! left at about 10:30, that exam was an insult to my intelligence

For the green lab books did we have to tick something or do we just do the experiments and hand it up?…..i already have it handed up but didnt tick anything..??

You didn’t tick anything if the project booklet to say you did the experiments. I’m sorry to say if you didn’t, that’s 10% gone, it happened in my school before

Let’s remove voltage from the Junior Science syllabus; post #1

 

Dear Mr/Ms Junior Cert Syllabus writer,

The time has come to question why the concept of voltage is still on the Junior Cert syllabus.
It is by far the most difficult concept for students (and indeed teachers) to grasp.
Consider a relevant extract from the Junior Cert Science syllabus

Set up a simple electric circuit, use appropriate instruments to measure current, potential difference (voltage) and resistance, and establish the relationship between them

Let’s take a look at potential difference (commonly referred to as ‘voltage’):

The following extract has been taken from the minutes of a History of Science meeting, in 2002.

John Roche, of Linacre College, Oxford, opened the session after tea, speaking on the concept of voltage. He began by claiming that almost every concept in electricity and electromagnetism is ambiguous, and the concept of voltage is one of the most incoherent. Its evolution is difficult to follow.

 Abbé Nollet, in the 18th century, distinguished quantity and degree of electrification. Others made similar distinctions between quantity and intensity or tension or pressure – what we would call voltage.

 Roche showed how the term “voltage” had come to be used nowadays in three different ways; for electromotive force, potential difference and (absolute) potential.

Volta defined electrical tension as the endeavour of the electrical fluid to escape from a body. Volta’s tension was more akin to a force, unlike the modern definition of electromotive force, which is a misnomer, being defined in terms of energy.

Ohm carried Volta’s concept to closed circuits with the idea that voltage was proportional to the difference in tension between the ends of a conductor. For Ohm, it was the gradient of electrical tension that drove the current.

Poisson introduced an entirely different concept, of charge divided by distance to a point, which Green called the potential. This was an analytical device only, arising from an analogy with Laplace’s gravitational potential function.

Kirchhoff reconciled Volta’s tension with Poisson’s potential function through the concept of energy or vis viva introduced by Helmholtz. From Kirchhoff, current is driven by the electric field in a conductor and voltage is related to the energy supplied, but physicists and electrical engineers do not usually think of them in this way.

All the earlier interpretations remain current, but with different weights, and most of the time voltage is seen as a driving energy.

 IOP History of Physics Group Newsletter, Spring 2000, page 65

So what exactly should we be telling our students about potential difference? How many (non-physicist) science teachers can define or explain potential difference? Maybe most can, but if so I would be very pleasantly surprised.

Would it hurt anyone if we replaced the syllabus extract above with something more simple, like the following?

Set up a simple electric circuit using appropriate instruments to light a number of bulbs in series.
Understand that for current to flow a power supply and a complete circuit are required.

The other aspects of the syllabus on electricity could remain as they are, but no Ohm’s Law, no experiment to verify Ohm’s Law, no mathematical problems based on Ohm’s Law, and no more mention of potential difference.

Junior Cert Science – a guide to answering Maths questions

Answering maths questions is a skill which intimidates many students at Junior Cert level.
the revsion page of thephysicsteacher.ie now offers a guide to answering maths questions in the exam. It includes a full set of maths questions and solutions taken from past-papers at higher and ordinary level.

Hopefully seeing it laid out in this fashion will encourage students to see (i) the importance of learning the formulae, and (ii) how straightforward the questions actually are once the formulae are known. There is a general belief that all formulae are in the new log-tables and that therefore nothing needs to be learnt off, whereas in fact only half of the formulae are there. The revision-guide includes a reference to these and where to find them. It also includes a set of practice questions.

No password required etc. Hope someone finds them useful. As always all I ask is that you follow the suggestion on the top of the first page in relation to saving paper.