Convection Currents in a beaker of water

 One of my A level students yesterday had never seen convection currents in water, so I set up this simple experiment for him. Into a large beaker I poured some cold water and at the bottom I placed a small coloured crystal.
I heated the water with a burner and watch as the water heated,  the water coloured by the crystal rose up in the beaker - not straight as the books suggest but in a more spiral direction until they reached the top when they spread out even more.

The water showed that it was less dense than the water around it because it was hotter and therefore it was lighter and rose to the surface - albeit not in a quite vertical direction.

There we are warm water rises and disperses the heat around the beaker from the bottom to the top.

New toys - old concepts - The Leslie Cube

A Leslie cube is a small hollow metal box with different painted sides. One is bare metal, the others are matt black, gloss black and gloss white.
The cube is filled with water and then heated until it boils.
Using an infrared thermometer we look at the temperatures  of the different surfaces. Each is a different temperature as seen in the pictures.

With a burner under the cube the water is heated until it is boiling. and the temperature of each surface is measured.
The bare metal surface came out as 49.3C

The Matt black surface came out as 97.9C

The smooth black surface as 95.9C

And the white surface as 97.0C

There is a difference. The bare metal was cooler by far. Now why might that be?

Maths GCSE Retake in Nov

Its time to start panicking. Do a set of exam papers ( calc and non-calc every week. Compare your answer to the marking scheme. The answer is not good enough all the working is required. Look at their working out in the marking scheme. How many marks would you get. Read the examiners report for each exam. It helps you know where others went wrong and perhaps how to avoid the pifallls.

Many schools don't use a Maths book. The revision guides are ok but a real Maths book with lots of questions are so much better. There are many to choose from amazon.


These books can help but any are good
Try to attempt one question from each section or exercise of the book each time you revise. It should take a little over two hours - almost the time of an exam paper.
Ideally you need to do this once or twice a week if you want a good grade.

The difference in a grade is about 2-3 hours of revision, so if you want the grade then you must do the learning. Maths is about practice as well as doing the learning how to do it.
Generally know how to do a sum is not the same as doing it.

Lego NXT Calculating force of gravity

I made a simple lego contraption to measure the force due to gravity.
The device consists of a lego retort stand with a switch at the top and a switch at the bottom.
We drop a lego tyre via a quick release mechanism. The tyre is connected from top to bottom by a piece of string that does nor impede the fall but guides the wheel down onto the switch at the bottom.
When we release the wheel at the top the timer starts and when the switch at the bottom is hit then the timer stops. Knowing the distance and the time then the NXT can calculate the force of gravity.

Lego NXT Science Bot as a Dynamics Trolly

When I was at school and when I taught in schools a few years ago dynamics trolleys with ticker tape timers were often used to teach the fundamentals of mechanics and newtons laws. My son at 18 and having just survived A level and GCSE physics had never seen such a trolley so with the help of Lego and an NXT brick here is an updated version. I have used this with my students to perform similar experiments without using the ticker tape timer. The NXT acts as a data logger and then uploads the information to the PC where the files are displayed as graphs in Excel.
Building Instructions for the Science Bot.
Program for the Science Bot

When the Science Bot is ready to go, the program removes the old data file and then records the number of 1/16 rotations (this corresponds to 1cm distance traveled. The distance and the time is recorded. This information is then sent to the PC as a comma separated file and then graphed in Excel.

The time is taken every 0.02 seconds which gives plenty of data per second.

As assembled the science bot has uses an acceleration sensor (not used in this program) and one of the old RCX mindstorms rotation Sensors.
The yellow box on the side is an old rpm sensor, which works independently of the mindstorms.

Summer Holidays - time to loose all those skills

The summer holidays come and for many students this is 6 weeks when they can relax, recover, go on holiday and forget about school and school work. This is so true because when the Autumn terms starts in September 3-6 months of recent work and skills will be lost and much of this work will have to be re-learnt and done again.

Although the summer holidays are good fun for students in year 10 going on to year 11 and those moving from AS to A2 this can be crucial. Some parents keep me on as a tutor though out the summer holiday to ensure that their children do not fall behind and loose too much knowledge.

If you can't do this then try to spend a day a week looking at each of your subjects, I would suggest 30 mins to 1 hr a week on each subject. spending just and hour a day, keeps the facts and skills in your head to that all that hard work does not melt away,

Exam Techniques

PANIC. Before the exam. This is Good. This might motivate good revision.
If you have revised well then you are well prepared.

• Check what exam you have the next day.
• Revise for that exam.
• Prepare everything you need to take to the exam.
• Get a good nights sleep before the exam. Go to bed a bit earlier and don't do any revision 1/2 hr before going to sleep.
• Have a good breakfast. If you don't normally then this is a good time to start.
• Read the front of the exam paper thoroughly. This reminds you of how many questions to do in each part.
• Read each question through to the end BEFORE you answer the question to make sure that you put the right answer in each part and do not get ahead of yourself.
•  In some papers the harder and more marks questions are at the end, These are often longer and take more time, so plan out your time - how much time for each question. 
• A wrist watch is excellent here for timing. You won't be allowed your phone. A watch with a second hand helps with the timing. If it helps take it off and put it on the desk in front of you.
• Answer all the questions you can. If you can't do a question then leave it and come back to it.
• Make sure all the keywords for this topic/section are used
• If you are running out of time then bullet point the facts
• For an essay question plan it first. Jot down a few notes. You can then refer to these in case you forget one as you write the essay.
• Come back to the questions you can't do. 
• Put down some answer. It might just be right. 
• If you have no idea than put down any relevant keywords or phrases.
• In some papers (like Maths) working from the back to the front can help. The harder/longer questions are at the back of the paper and you get these over when you are freshest and the easier ones come later.
• When your finish go back and check your answers. Read the question again and check you have answered what was asked.
• Remember ....  RTFQ Read the F..... Question
• RYA Read you answer. I often feel I am the first person to read what you have written
• Sometimes it right to go with your gut feeling answer to a question. It is often the right choice.