The topic "Light" is mainly split into 3 parts: Reflection, Refraction, Lenses.
A common testing point in all of these parts are ray diagrams. As such, it is important for you to practice drawing all the different diagrams ahead of the exam.
Ray Diagrams To Master: 💪🏼
1. Mirror Diagrams for Reflection
2. Refraction of light ray diagrams (more dense-less dense, less dense-more dense, critical angle)
3. Lenses
When practicing ray diagrams, there are a few things to note:
a. Direction of arrows (Arrows should always be directed into the observer's eye! If you draw arrows coming out of the eye, you are implying that our eye emits light)
b. Dotted/Bold lines (Dotted lines are for light rays that are behind the mirror (i.e., virtual plane)
c. Orientation/size of the image (for different case, the image produced may be bigger, smaller, or inverted)
Paying attention to these points will help in your practice.
Part 1: Reflection 🪞
Apart from ray diagrams, the other concept to know for reflection is that the angle of incidence is equal to the angle of reflection.
Part 2: Refraction 🌊
a. First, you should understand that light rays bend because of the change in speed of light when travelling in different mediums.
b. Next, you will need to pay attention to whether light rays bend away/towards the normal (this depends on what medium the light is travelling towards).
c. Know the formulas for refractive index:
(i) n1*sin(i) = n2*sin(r) where n1, and n2, are the refractive indexes in mediums 1 and 2 respectively
(ii) n = c/v where c is the speed of light in vacuum and v is the speed of light in the medium
d. Know the conditions for critical angle and how to calculate it
Part 3: Lenses 🔎
a. The main thing that students struggle with is drawing the different lens diagrams. This, however, requires practice and some memorisation of the different scenarios. I would suggest spending time sitting down and practicing all the different scenarios and commit them to memory
b. Along with the ray diagrams, you should also know the applications of the different lens scenarios
Final notes:
For those struggling with light, I find that this website has some good notes and practices for this topic: https://evantoh23.wordpress.com/
Do forward this post to those who may benefit from it! 📢
As always, if you need help please do drop a message to me or in our discussions group.
Hope this helps,
ThePhysicsPage 🤘🏻
