Friday 30 January 2015

Leaving Cert physics

Over the past number of years, the number of students taking Leaving Certificate physics has fallen dramatically.

This has been caused by a number of factors, but the main issue seems to be the perceived difficulty of the subject. This attitude to physics is completely unfounded as a few practical steps will result in a huge increase in marks.

First, as definitions form the backbone of the course, this is where students should focus their attention to start. In most cases, a mathematical formula will result from careful reading of the definition.

An example of this is as follows: Newton's Law of Gravitation states: "All objects are attracted towards each other by a force which is directly proportional to the product of their masses and inversely proportional to the square of the distance between them."

If we say that the masses of the two objects are M1 and M2 respectively and that their centres of mass are separated by a distance , 'd', say, then the force would be calculated as

where 'G' is a constant known as the universal constant of gravitation.

We can see clearly that the numerator is the product of the two masses and that the denominator is the square of the distance between them.

This idea can also be reversed. Imagine you are in the exam and you have forgotten the definition of momentum. If we open our log tables, we can look up the formula for momentum in the mechanics section. It says that momentum = mv. If we translate this into English we see that "The momentum of a body is the product of its mass and velocity". Not only can we work out the definition of momentum, we can also find the units in which it is measured. Mass is measured in 'kg' and velocity in 'm/s', so it makes sense that momentum is measured in 'kg m/s'. It is essential that all students know what each quantity on the curriculum is measured in.

As teachers we are also continuously learning from our students. A few years ago one of my students had the idea of recording all of the Leaving Cert physics definitions on to his computer and transferring them to his MP3 player. This meant that he could be learning them on his way to school or on long car journeys, etc. This has proven very productive with many of my students.

Section A Experiments

Experiments form the basis of Section A of the physics exam, which is worth 120 (30pc) of the overall marks available on the paper. There are around 25 major experiments on the course, which appear on the exam with monotonous regularity. It makes perfect sense for students to write out the experiments so that they can be revised very quickly. This could easily be done in less than about 30-40 pages.

Most experiments involve manipulating a table of results and then drawing a graph of some description before coming to some important conclusion. The following steps should always be taken:

1 Make sure that the units given in the table are the standard units of measurement for that quantity. If they are not you should convert to standard units before proceeding.

2 All graphs should be scaled properly and given a title.

3 Each axis should be labelled and the correct units of measurement given.

4 All points should be plotted carefully (in pencil), and each plotted point circled. This distinguishes between plotted points and accidental marks on the page.

5 BEST FIT. It is imperative that when drawing the curve (usually a straight line) that you draw the curve of best fit. This means that you draw a line that shows the best average distribution of the points, not necessarily the line containing the biggest number of plotted points. The following example illustrates that the line of best fit may not pass through any points at all.



Force/N .





Learn all of these experiments well and you will be rewarded for your work.

Section B Theory

Students are required to answer five questions from this section. In total there are 280 marks available for this section (70pc of the overall). Students can make some tactical decisions which will maximise their marks. First, Q5 is a must. This involves several short questions. These are mainly definition-based or involve a quick calculation -- an easy way of picking up marks.

If we analyse Q12 we see that we have a choice within the question. It is wise to choose this question for this reason. Typically, this question has four parts and students need to answer two. At this stage we have answered two of the five questions in Section B, so we just need to pick three questions from the remaining six questions to finish the exam paper.

General Notes to consider

Do not 'Carpet Bomb' a question

Students insist on writing down everything they know about a topic when asked a question. This immediately shows the examiner that the student does not understand the topic and should therefore be marked accordingly. It is admirable that a student would learn something off by heart, but it is important that the student understands what the topic is about.

It is essential that all students read the question carefully and analyse exactly what the examiner wants to know. For example, if you are asked to explain how a student would measure the acceleration of an object which forms part of the experiment which we study to prove Newton's Second Law, then you should simply explain how to measure the acceleration of the object, not go through the full detail of the experiment.

Clear Diagrams

Diagrams should be drawn very clearly with pencils and rulers, not freehand. They should be labelled clearly and large enough that the examiner can see the layout of the equipment.

Study timetable

It is impossible to learn a large quantity of physics in a short space of time. It should always be studied in bite-size chunks where ideas are learned properly. Be realistic about how much time will be required to study a topic. A few hours will suffice to learn the Sound chapter as it is quite short, but Electricity may take up to three weeks, at three to four hours per week.


Students should repeatedly test their timing and quality of answering. Questions in Section A should take up to 18-20 minutes to complete, whereas questions in Section B should take 22-24 minutes. When you have completed a few questions from Leaving Cert Papers, log on to www.examinations.ie to check your answers. This is vital. Physics is very straightforward to learn when study is approached in the right way: 'little and often' is the way to success. With more than 20 weeks left after Christmas we still have lots of time to ice the cake.

NEXT EXAM SUBJECT: Business Studies

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