# Lesson planning of Light Travels in Straight lines

Lesson planning of Light Travels in Straight lines

Subject General Science

Students` Learning Outcomes

• The students will;
• Investigate that light travels in a straight line.
• Explain the formation of shadows and eclipses.
• Predict the location, size and shape of a shadow from light sources relative to the position of objects.

Information for Teachers

• Light is obtained from luminous sources and spreads all around.
• Light from its source travels in straight lines
• When light is obstructed by opaque objects but never whirls along the opaque object.
• As no light passes through the opaque object so it casts shadow of that object.
• An eclipse is the shadow of either the Earth on the Moon or of the Moon on the Earth.
• There are two types of eclipses, lunar eclipse and solar eclipse.
• Lunar eclipse is formed when Earth obstructs the sunlight reaching the Moon.
• Solar eclipse is formed when the Moon obstructs the sunlight reaching the Earth.
• Location of shadows is changed as the distance between light and the object changes.
• The size of shadow increases as the distance of light source from the object decreases and vice versa. Due to this fact the shadow of objects changes dramatically throughout the day.
• Shadow has the same shape as that of object.

• While teaching the lesson, the teacher should also consult textbook at all steps wherein and whenever it is required.

Material / Resources

Writing board, chalk/marker, duster, pointer, a candle, three small wooden pieces, a book, a shoe box, a torch, and three pieces of hard cardboard, scotch tape.

Introduction

• Do the following warm up activities to involve the students.
• Ask the students, “Have you ever seen a shadow? Most of the students will say ‘yes’.
• Select three students. Ask one of them to place a white paper on the wall.
• Ask the second student to throw light from a torch on that white paper.
• Instruct the third student to place his hand in the path of torch light.
• What do you see on the chart? (Students` response would be as; Shadow of hand)
• Ask that student to change the shape of shadow of his hand and others to observe.
• Conclude that shadow has same shape as that of object.

Development

 Activity 1 Bring three cards A, B, and C, three wooden blocks, a nail, scotch tape and a torch in class. Make a small hole with the nail at the center of each card. Attach the cards on one side of each wooden block with scotch tape to keep the cards in vertical position. Ask a student to light a candle and place it in front of the hole of card A. Ask another student to adjust card C, so that the flame can be seen. Instruct them to place card B in between cards A and C. Guide the students to adjust the cards so that flame can be seen through all the holes.

 Activity 2 Bring a big ball (like a football), a small white ball, a table lamp and a marker. Select a place in the center of class and direct the students to sit around the activity place. Adjust the table lamp in a suitable position and turn it on. Direct a student to make a mark with marker on the big ball and show to whole class. Guide them to hold the big ball in his hands so as the mark should face the table lamp. Direct another student to hold white ball in a position between light and the big ball. Help him to adjust the white ball such that its shadow should fall on the mark. Inquire the students: “What is an eclipse?” (Expected answer would be as; It is a shadow). What is the name of this eclipse? (Expected answer would be as; Solar eclipse). Make them consider that lamp as Sun, small white ball as Moon and a big ball as the Earth. As sunlight is blocked by the Moon so it solar eclipse. What will you see in the sky if you are located in your city? Explain them as white ball (Moon) obstructs the light (sunlight) so city becomes dark and you can`t see the bulb (Sun) directly. How can it be produced a lunar eclipse from this arrangement? (After students` response, tell them for lunar eclipse shadow of Earth falls upon Moon so interchange the positions of both balls).

Conclusion / Sum up

• Light travels in straight lines.
• All opaque objects are light blocking and cause shadows.
• When Moon lies between Sun and Earth then solar eclipse is formed.
• When Earth lies between Moon and Sun then lunar eclipse is formed.
• Location and size of shadow could be changed but its shape is retained.

Assessment

• Ask the following questions: as;
• If light could turn around the objects, what type of shadow will be obtained? (Expected answer would be as; No shadow is formed)
• Have you ever raced with your own shadow? Who is the winner? (Expected answer would be as; shadow remains with the object)
• How can you change the size of the shadow? (Expected answer would be as; by changing distance between light and object)
• Do you ever see shadows in a dark room? (Expected answer would be as; No).on what side of the object, its shadow is obtained? (Expected answer would be as; behind the object)
• What is the name of eclipse which can be observed at daytime only? (Expected answer would be as; Solar eclipse)
• Teacher is also required to involve the students in solving the problems given in the exercise at the end of unit/chapter.

• Ask the students, “In what ways did early people measure and tell time before the clocks were invented?
• After the students response tell them that early people used directions and lengths of shadows to tell the time.
• To elaborate this give them an example of the shadow of a tree which changes its position all the day.
• Ask them to draw the diagram.
• Encourage the students to observe and make a list of the objects / things which can`t cast shadows. Note in their notebooks,