Term 3 Learning Points

Hi guys,

Today I will be sharing with you guys my learning points in Term 3. This post will be mainly about what I have learnt in Term 3.

So in through this term, I have been learning Physics, mainly, light, reflection, refraction. So let me explain to you guys now.

So what is light? Let me now define it for you guys. Light is a form of energy that enters our eyes and enables us to see things. Light travels a super speed, at the speed of 3X10^8 meter/sec. It is even faster than the speed of sound. The speed of light therefore allows to see the sun so quickly when it rises. Light is also essential in our lives. It allows us to see things and therefore, interact with them. Without light, the whole world will be in darkness.

So what is reflection? Reflection happens when light strikes on a surface. Reflection happens everywhere, however, reflection does not mean the image reflected can be seen. In reflection, there is always an incident ray and a reflected ray. The incident ray is the ray from the light source whereas the reflected ray is the ray that is reflected. At the point where the incident ray touches the surface, the point will be the point of incidence. Perpendicular to this point and surface, draw a line. The line will be what we call the normal. In between the normal and the incident ray, the angle is called the angle of incidence. The angle of incidence will be equal to the angle of reflection, which is the angle between the normal and the reflected ray.

The diagram will then look something like this

There are also 2 laws of reflection. The 1st law states that the incident and reflected ray and normal all lies on the same plane. The 2nd law of reflection then states that the angle of incidence is equal to the angle of reflection.

In reflection in a mirror, there is also a law for the image that will form. The image will have the same size as the object itself, is similarly orientated, laterally inverted, is the same distance from the mirror and is virtual. Some of you may start wondering what is a virtual image, why is the image formed behind the mirror?

So let me answer these questions now. Firstly, targeting the question on why the image is formed behind the mirror.

What we mean by the word behind here, is that when you look into the mirror, you seemed to see yourself inside the mirror, and it seems the same distance from you to the mirror and the image to the mirror. So the word behind here does not literally means behind. With this, I shall move on to the next question, why is the image virtual. The image is virtual as "behind" the mirror, there is no light source and therefore, no actual light rays meet at the image position, and hence, the image is virtual.

Now I will move on to refraction. Refraction is rather different to reflection. In refraction, light will pass through from a denser medium to a less dense medium. When this happens, the speed of light changes, and therefore, refraction happens. The light will bend away or towards the normal according to the density of each medium. If light passes from a denser medium to a less dense medium, the light will bend AWAY from the normal. Vice versa, if light passes from a less dense medium to a denser medium, the light will bend TOWARDS the normal. For example, light passes through this order at angle of 30 degree: air, glass, air. The angle of refraction in the glass will be lesser than the angle of incidence. After passing through the glass, the angle of refraction in the air will be larger than the angle of incidence in the glass.

In Conclusion, there are many laws of reflection and refraction and each law will cause a difference in the result. Just a short summary of this post. Angle of incidence is the same of angle of reflection in reflection. Perpendicular to the point of incidence and the surface, is the normal. Refraction happens when light passes through different mediums of different density, which will affect the speed of the light, causing the light to change its angle of refraction.

Reflection on this topic (NOT REFLECTION OF LIGHT):

I feel that this topic is easy yet complicated. Easy as in most of the information are common sense and memorising this topic will allow us to score well in tests. However, the flaw is that it is rather complicated at times. There are many parts that we have to study and we must also be good in math to score well in Physics. Physics and mathematics are interlinked. Therefore, I find this topic easy yet complicated.

Thanks,
Aloysius Chan