Before you read this, I suggest you read post 22.4. In post 19.21, we saw that a ray of light passing from air into glass (or any other dense, transparent medium) is bent towards the normal to the interface between them, as shown in the picture above. In this picture A is a point in… Continue reading 22.5 Total internal reflection

A wave bounces back from a wall that it cannot destroy or be propagated through. This bouncing back is called reflection and is shown in the picture above. We are usually interested in reflection of electromagnetic radiation. For example, light is reflected by a mirror. A mirror is something that cannot absorb or propagate light… Continue reading 22.4 Reflection

Before you read this, I suggest you read post 22.1. The magnifying glass is a bi-convex lens that uses the light from an object to trick the eye into thinking the object is bigger than it really is. The way is works can be explained by ray-tracing, as shown in the picture below. In the… Continue reading 22.3 The magnifying glass

Before you red this, I suggest you read post 22.1. A projector is a device that uses light emitted by an original image to produce a larger version of that image on a screen (the projected image), as shown in the picture above. In this picture the blue arrow points upwards but in the projected… Continue reading 22.2 The projector

Before you read this, I suggest you read post 19.21. The picture shows an object (in yellow) with two convex curved surfaces. This object is made of a material whose refractive index in air, n, is greater than 1; we will suppose that this material is glass but it could be any transparent material with… Continue reading 22.1 Refraction at curved surfaces – lenses

Before you read this, I suggest you read post 21.23. In post 21.23 we met the idea that the sequence of bases in mRNA determined the sequence of amino acids in a protein. The question then is – what sequence of bases will code a given amino acid sequence? We shall see that the experiments… Continue reading 21.24 The genetic code

In post 21.11, we saw that genes are made of DNA and that genetic information is code in the sequence of its bases; more details on the importance of this base sequence were given in post 21.12. But this raises a fundamental question. How does a DNA sequence determine who we are? How does my… Continue reading 21.23 Implementing genetic information

Before you read this, I suggest you read post 21.21. If you’ve read post 2.21, you may wonder why anyone would be interested in torsion of a cylinder. The reason is that long, thin cylinders (rods) are used as shafts to transfer rotational motion in many different types of machines. The drivetrain of a car… Continue reading 21.22 Rotating shaft

Before you read this, I suggest you read post 20.19. Torsion is the deformation you apply when you start to remove a screw-top from a bottle. In the picture above, torsion is applied to a cylinder, with a fixed base, so that A moves to A’. O is the centre of the top face of… Continue reading 21.21 Torsion

Before you read this, I suggest you read posts 21.17 and 21.19. This post is a continuation of post 21.19. I am going to use the ideas in post 21.19 to develop the equations stated, without proof, in post 21.17, that allow us to calculate the deflection and maximum stress in two examples of beams:… Continue reading 21.20 More about beams