Optical Image


Objects between F and lens

Hold a magnifying glass above a page. The alphabets are magnified.

Objects beyond 2F

Now hold it in front of you and look at your friend. Your friend is upside down and appears smaller!

Try this!

Stand in front of a tree and hold a piece of paper upright in your hand, so that the paper faces the tree. Hold your magnifying glass as if someone wants to read the blank paper (haha!). Then slowly move the magnifying glass away from the paper, towards the tree. What do you see on the paper as you move the magnifying glass?

Try it!


Interactive Flash
Get Adobe Flash player

In the Flash above, F represents focal length.

Real image is an image that can be projected on a screen. Virtual image can not be projected on a screen but can be observed when looking directly at the optics.


If you like a copy of this Flash, get it here!

A Level Applied ICT

Here’s some revision materials for A2 Applied ICT (9713). Click the top-right button of the document viewers below to go full-screen!


Chapter 7.1 & 7.2 - Computer Networks

Past exam questions compilation

Note that these compilations are incomplete! All of these files are Word .docx files. If you add even more info to them, please kindly share your edit by emailing the Word file as email attachment to [email protected] 🙂 Continue reading A Level Applied ICT

My ASEAN Undergraduate Scholarship (AUS) and Other Scholarship Timeline

After a quick search on the Internet, I was very surprised at how little information I can find on AUS scholarships provided by Singaporean universities.

I am applying for academic year 2014/2015. Here I attempt to list down things I did, as a Bruneian student, in a timeline.

Note that this is no way an official guide, but it does help you see the things you need to do. You shouldn’t also follow the deadlines listed here. Notice that they are different for every country every year.

Here are more details: Continue reading My ASEAN Undergraduate Scholarship (AUS) and Other Scholarship Timeline

A Level Physics Common Questions

I have compiled a list of questions from the Cambridge past year papers. They might be incomplete, but they cover a lot!

  • Download the PDF version for easy viewing/printing.
  • Download the Word version if you wish to make it even better. Please kindly share your edit by emailing the Word file as email attachment to [email protected]


Limiting Equilibrium


Why are there two limiting equilibrium? Why does friction acts upwards? Why does friction acts downwards? Why is the object about to move up? Why is the object about to move down?

All these questions and concepts appear contradicting, but trust me, it’s easy once you get the hang of it.


This post is written with the assumption that you know the concept of forces and equilibrium. This post helps you to understand limiting equilibrium, but does not help you with calculations or problem solving.


Limiting equilibrium is the state a particle is in when it is on the point of sliding.


It’s best to learn with example.

Imagine a small ring threaded on a rough rod which is fixed vertically. The ring is pulled upwards with a string at an angle, and the ring is in equilibrium.

Play around with the interactive flash below. Explanations are below the flash.

Interactive Flash
Get Adobe Flash player


Initially, with a small force, the ring is about to slip downwards, and thus by definition, the ring is in limiting equilibrium. Frictional force tries to oppose this by acting upwards.

As you increase the force applied, there will be an instance when the vertical component of the force balances the downward force due to gravity. Frictional force does not act during this instance.

As force increases, the ring has the tendency to move upwards now. It wants to move upwards, but the friction acts downwards and stop the ring from moving. (Previously the ring wants to move downwards due to gravity.)

As force increases, the ring will reach limiting equilibrium again, but this time, it is about to slip upwards.


  • Note that there are 2 limiting equilibrium in this example.
  • There is actually a range of force which when applied, will not cause the ring to move.