resistor colour codes

I saw this cartoon and it reminded me of the resistor colour code quiz we made up in class on Friday using Shane’s questions.  Can you remember how to work out the value of each resistor?  Let’s see if you can all do it on your own this time.

You might want your own copy of the resistor colour code chart as you won’t be able to see my classroom poster this time.  You can get a chart online here or as a pdf here.  Click once on each picture in the quiz when you are are ready to see the answer.  Clicking again will move on to the next resistor.  

Don’t click ahead too quickly or you will see the answer before you have worked it out.  

Click here to take the quiz

electronic breadboards

We discussed laying out of circuits today when I introduced the bicycle lights project we will be working on for your final assessment.  

One of the methods for laying out a circuit is to use a breadboard.  These youtube videos are a good introduction to using breadboards in electronics.  Watch the upper clip first as the lower clip is designed to follow on from this one.  Post a comment if you have any questions and I will try to provide an answer.

Note: we have met the 555 timer chip from the 2nd clip in our computer simulation sessions – remember the blinking LED exercises? 

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significant figures

In our discussions yesterday, one of the things that cropped up was that we need to revise the material covered before the summer holidays.  I thought I would make a start on this by looking at significant figures.  

You might have heard me referring to “calculator vomit” in class.  This is an expression I use whenever people simply write down the answer provided by their calculator, without thinking about whether or not the number of decimal places reported is appropriate.  In Physics, we can avoid “calculator vomit” by using significant figures.  I’ve provided some links below to direct you to sites that explain what significant figures are and how to use them. 

http://www.ausetute.com.au/sigfig.html

http://www.chem.sc.edu/faculty/morgan/resources/sigfigs/index.html

http://www.staff.vu.edu.au/mcaonline/units/numbers/numsig.html

http://www-users.york.ac.uk/~mb55/msc/maths/sigfig.htm

 

If you’ve read through some of those pages and feel that you are ready for a test, you can try your luck at

http://lectureonline.cl.msu.edu/~mmp/applist/sigfig/sig.htm

Note: these links might also be useful for AH pupils analysing their investigation data.

projectiles – moving in 2 directions at once

One of the things we spoke about today was the difficulty of dealing with horizontal and vertical velocities one at a time when we analyse the motion of a projectile. I have uploaded this diagram to see if it will help you see how the horizontal and vertical velocities change as we look at different parts of the trajectory. You can click on the diagram to see a larger version if you like.

Hopefully you can see the arrow I have drawn in for the velocity of the projectile at any point – it’s the brown arrow. I have added blue and green arrows to this.

The green arrows show the horizontal motion of the projectile. The green arrows stay the same length throughout the flight because there is no unbalanced force acting in this direction (Newton’s 1st Law told us that balanced forces result in a constant speed).

Looking again at the diagram, you should notice that the blue arrows show the vertical velocity of the projectile. The blue arrows change as we move along the trajectory. For the first half of the diagram, the blue arrows point up because the projectile continues upwards towards it maximum height (called the apex). As the projectile travels towards the apex, gravity acts to slow it down – we have deceleration due to gravity. This is why the blue arrows get shorter – the length of the arrow shows the size or magnitude of the velocity. Once it has passed the apex, the projectile falls downwards. The diagram shows that the blue arrows point downwards during the second half of the journey. As the projectile falls, it’s vertical velocity increases (it is speeding up) and this is shown by the blue arrows getting longer. This is acceleration due to gravity.

Notice that all the time that the blue arrows change their length and direction, the green arrows always have the same length and point in the same direction. Horizontal velocity is constant in projectile motion.

We can analyse horizontal motion quite easily using the relationship between speed, distance and time.

To analyse the vertical motion, we need to use the equations of motion.

Large Hadron Collider – lock up your protons!

Some of you have been asking why people are talking about the world ending on Wednesday.  Funny how this question has arisen whenever I hand out homework!  I’ve spoken about the Large Hadron Collider and some of you may have seen the BBC coverage on Big Bang Night last week.  They also have some special programmes scheduled to commemorate the day the LHC is switched on, including a particle physics radio programme with Alan Alda, Ben Miller, Eddie Izzard, Dara O’Briain and John Barrowman but then I could have told you that Physics is the new rock’n’roll 😉

I’ve also found a rap video about the LHC.  The clip seems to stream slowly so you might want to start it and hit pause to let it load fully before playing.  Enjoy!

physics in a lift

We had some fun in the school lift today, trying to confirm what we had read about apparent weight.  Although the effect was small, we managed to spot the same effect as was demonstrated by David jumping off a desk with a set of 100g masses hanging from a Newton balance.  

I found a link that puts some words around our findings.  Follow this link to find out more.

image: “elevator” by Beard PaPa