LIGHT ENERGY (CONTINUED) Lesson note

PROPOSED LESSON PLAN/NOTE FOR THE EIGTH WEEK ENDING 4^th NOVEMBER, 2022

2022/2023 ACADEMIC SESSION

SUBJECT: BASIC SCIENCE

TOPIC: LIGHT ENERGY

CLASS: GRADE 9

NUMBER OF STUDENTS: 16

AVERAGE AGE: 13+ YEARS

GENDER: MIXED

PERIOD: 7^th AND 8^th PERIOD ON TUESDAY AND FRIDAY RESPECTIVELY

TIME: 1:20-2:00

DURATION: 40 MINUTES

DATE: 31/10/2022

SPECIFIC OBJECTIVES: By the end of the lesson the students should be able to;

1. discuss refraction of light and its application;

2. discuss visions;

3. describe dispersion of light and rainbow.

ENTRY BEHAVIOUR/PREVIOUS KNOWLEDGE: The students have already studied part of this topic in the previous week.

INSTRUCTIONAL MATERIALS: pin-hole camera, diagrams, posters.

INSTRUCTIONAL METHODS/TECHNIC: Questions, simulation, visual.

INTRODUCTION: Question pose to the students includes

Question 1: What is refraction?

STEP1: REFRACTION

    Sometimes, light rays do not bounce off a surface. Instead, the light rays passes through it, but in doing so they bend from their original path. The phenomenon of bending of light as it passes from one medium to another is called refraction of light.

   The bending occurs because light travels slower in a denser medium.

                                        P               N

                       Air(Medium1)                             

                                                     O

                      Water(Mediu2)          N    

                                                 Refraction

·        When a light ray travels from a less dense optical medium to a more dense optical medium, it bends towards the normal at the surface of separation of the two media.

·        When a light ray travels from a more dense optical medium to a less dense optical medium, then it bends away from the normal at the surface of separation of the two media.

APPARENT DEPTH

Take a coin and a 500 ml beaker filled with water. Drop this coin into the beaker and wait until the coin settles down and water comes to rest. Now, observe the coin from the position shown. What do you observe? You observe that the coin appears to be raised slightly. This happens sue to refraction of light. The light rays coming from the coin get refracted as they leave water. Thus, we see the image of the coin slightly raised above the surface of the beaker. This is the apparent depth of the coin. Similarly, when we look vertically downward, into a swimming pool of water, the bottom of the pool seems closer than it really is. The refraction of light at the surface of water makes ponds and swimming pools appear shallower than they really are. As apparent depth is smaller than real depth, amateur swimmers should always check the mark of depth before entering the pool, otherwise they may get drowned.

STEP2: VISION

   We see with our eyes. Each eye has a lens, an adjustable opening called the pupil, dark chamber and a screen called the retina. Light rays reflected off from objects passes through the cornea, a clean protective shield. Then, it goes through an opening, the pupil, which is an adjustable hole in the iris. The iris is a circular diaphragm, which gives the eye its colour. Muscles in the iris change the size of the pupil. The pupil closes down in bright light and widens when the light is dim. Behind the iris is the lens. Ciliary muscles hold and control the shape of the lens, thus focusing it to view objects at different distances. The light rays then pass through the dark chamber to the screen called retina at the back of the eyeball. The retina contains the nerve cells. When light strikes on them, they send a signal to the brain through the optic nerve at the back of the retina. As the brain receives the signal, we are able to see objects.

    The light rays which enter the eyes get refracted and finally reach the retina and form the image. 

STEP3: DISPERSION AND RAINBOW

     Dispersion is an effect where different colours of light are bent differently and white light separates into its component colours. You must have seen a rainbow in the sky after the rain. It is formed because when sunlight (white light) passes through tiny droplets of water, it splits into seven colours-violet, indigo, blue, green, yellow, orange, and red (can be remembered as VIBGYOR). This spectrum is similar to one you obtained using a prism. Here, rain drops are causing light to disperse.

Rainbow

   Rainbow is an example of dispersion. A rainbow is most often viewed as a circular arc in the sky.

EVALUATION:

1. Discuss refraction of light and its application;

2. Discuss visions;

3. Describe dispersion of light and rainbow.

SUMMARY/CONCLUSSION:    Sometimes, light rays do not bounce off a surface. Instead, the light rays passes through it, but in doing so they bend from their original path. The phenomenon of bending of light as it passes from one medium to another is called refraction of light.

ASSIGNMENT:

1. Discuss refraction of light and its application;

2. Discuss visions;

3. Describe dispersion of light and rainbow.