1. Converging lens (convex lens) Converging lens, also known as convex lens,  is thicker at the centre. Below shows some examples. In O-level, we learned about symmetrical converging lens. i.e. the curvature of the lens are the same on both sides. As light rays pass through the converging lens, the rays come closer together . Take note that the bending of light, refraction, takes place on the air-glass boundaries on both sides of the lens (as shown above). But for easy drawing, we draw the bending at the imaginary centre vertical which passes through the optical centre as shown below. If the parallel rays are at an angle, the light rays will converge on a point P which lies on the focal plane. 2. The 3 Rays The following 3 rays are important for us to construct the ray diagram and locate the image. We always draw these 3 rays as they have rules to follow, hence guiding us in our drawing. Refer to the video below for better understanding of the 3 rays. 3. The 4 Key Scenarios Depending on the distance of the object to the centre of the lens (object distance u), the kind of image you get varies. Refer to the video below for the better understanding of how the various images are formed. 3. The Pattern Besides knowing the 4 key scenarios, it is important to know how the image behaves as the object is moved towards the lens. In general, as the object (starting from a distance of >2f) moves closer to the lens, the image will move further away from the lens and the size of the image becomes bigger. But when the object is within a focal length, as it moves closer to the lens, the virtual image moves closer to the lens and it becomes smaller compared to the image previously. But the virtual image is always bigger than the object. Refer to the video for better visualisation and understanding.

A pin in the beaker of water appears higher than its actual position due to refraction of light. In this experiment, you have to adjust the pin at the cork to a suitable height, such that the pin and the image of the pin inside the beaker of water is aligned and that ‘pins at position of no parallax’ position. The video below guides you in adjusting the height of the pins to locate correct height.

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. Example A Example B Example C Example D Example E Example F Example G Example H Example I Example J

In this post, it shows a free-falling ball from a height of 1.0 m. During the impact, the direction of the force on the ground is downwards and the force on the ground by the ball is greater then the weight. As the ball is free-falling, the only force acting is its weight downwards. Hence a common misconception is to think that the force on the ground during impact is equal to the weight. This is wrong. The normal force (force on the ball by the ground = stopping force on the ball by the ground) is greater than the weight . The force on the ball by the ground is equal and opposite to the force on the ground by the ball . Hence the magnitude of the force on the ground is greater than the weight . Similar concept can be applied if a man jumps off from a height. But in this case, the man’s leg will exert a stopping force over a short distance. That stopping force, once again, is greater than the weight of the man.