# Category Archives: Quick Revision

## Potential Divider Summary

## Different Lens Ray Diagram questions

Drawing ray diagrams for converging lens come in many forms. But the basic concepts needed are the 3 rays (which have rules to follow) to locate the image. The following ray diagrams for the 4 scenarios must be learned well, together with the respective image characteristics and applications.

With the basic concepts learned, when questions are asked in different ways, you should be able to draw the ray diagrams. Refer to some different ray diagram questions below and their video tutorials.

Click the followings for other lens ray diagram questions. https://evantoh23.wordpress.com/2010/11/09/20101109converging-lens-important-concepts/

https://evantoh23.wordpress.com/2015/08/27/olevel-sp-p1-focal-length-of-lens-using-distant-object/

## Vector Diagram – Parallelogram Method for 4 different kinds of questions

For Combined Science Physics Olevel, when constructing vector diagram, a method called **Parallelogram Method** is commonly used.

**Parallelogram Method** is used when **2 forces are known**, and the** resultant (net) force R**, can be found.

Below show **5 different variations of questions** when can be solved by using Parallelogram Method:

(A) Body has **acceleration**, **forces are unbalanced**, there is a **resultant force R** *(Newton’s 2nd law)*

(B) Body **at rest**, **all forces are balanced**, there is **no resultant force R** *(Newton’s 1st law)*

(C) Body moving at **constant velocity**, **all forces are balanced**, there is n**o resultant force** *(Newton’s 1st law)*

(D) Finding **unknown force** (with **resultant force R + another known force are given**)

(F) **Vector diagram is applicable to all vector quantities **(with magnitude and direction). Not just for forces.

Click here to view video tutorials on how to construct parallelogram step-by-step

For Pure Physics, another method is the closed-loop triangle, where only 1 known force with 2 other unknown force. Click here to view the video tutorials.

## Pendulum: Displacement-time vs KE-time graphs

Basic Concepts of the pendulum:

Refer to this post for the factors that affect the period of the pendulum