Grade: VIII
Time period: Two periods
1. Objective
To teach refraction by involving children in doing hands-on activities and conducting inquiry
2. Learning Outcomes
Students will be able to understand
- That light bends when it travels at an angle from rarer medium to denser medium and vice versa and predict the direction of bending of light.
- That total internal reflection occurs when light travels from denser to rarer medium and the angle of incidence is greater than the critical angle.
Activity 1: The Path of Light
Students arrange the match boxes containing holes in the inner tray and observe from one end. Teacher elicits responses from students to help them deduce why the object on the other side is visible in a particular arrangement (where the holes are in a straight line) and not otherwise. Children by themselves arrive at a conclusion on the path of light.
Activity 2: Reappearing coin – Effect of Refraction
Children observe a coin in an opaque container. Children are questioned on how the coin appears once water is poured. Children’s reason must be elicited on this and this should be formulated as a hypothesis and put to test. For instance, children may say the coin has started floating and this can be put to test by touching the coin inside the container and ensuring that it is resting on the bottom surface.
Students should be guided through questioning to develop an understanding that the light ray bends and hence reaches the eyes of the observer. Students also draw the path of light through which it reaches the observer’s eyes.
Experiment: Observing the path of LASER in air and water
Children are probed on the methods by which they can test the hypothesis that light bends when passing from water to air and reaches the eyes of the observer. Teacher can pose questions like - "why are we not able to see the bending of light?" and elicit from them that white light is not visible to the naked eye. Then questions like what can be done to make light visible or have you seen any kind of light which is visible will help elicit the idea of using laser from children. The arrangements for testing the bending of light can be elicited from students. Children should also be able to make observations on how light bends when it passes from water to air and how light bends from air to water.
Activity 3: Disappearing Coin – Effect of Total Internal Reflection
A coin is visible when observed from the side view through an empty glass placed over it. After water is poured into the glass, the coin disappears when observed from the side view. Students are asked to hypothesize the reason for the disappearance of the coin based on the conditions for an object to be visible, i.e. An object is visible only when light from it reaches the eye. The teacher then takes students through an investigation on what could have caused the change in the direction of light, thus introducing the phenomenon of Total internal reflection to children.
Term: Term 3
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