Mirrors and Images
Based on their experience with Activity 6, your students should have some understanding of incident rays, reflected rays, and the general behavior of mirrors. At this point, therefore, your students should be ready to be introduced to the different types of reflection that may occur. Explain to your students that reflection of light from a smooth mirror-like surface, such as water, results in a clear image and is known as specular reflection. When the surface of a lake or pond is wind-blown, however, the incident rays strike the surface of the water at many different angles. As a result, the reflected rays produce an unclear image. The reflection of light from such a surface is called diffuse reflection. To illustrate this concept, have students, take a piece of aluminum foil that is smooth and observe the clarity of the image. Then ask them to roll the aluminum foil into a tight ball, open it back up, and observe the image. Have students record their observations in their science notebooks.
You may also want to carry out a brainstorming session before beginning the main activity. Place students in small groups and have them list uses of mirrors, types of mirrors, or places they have seen mirrors. This is a good warm-up activity to encourage students to clarify what they learned in Activity 6 and to further extend their understanding of mirrors. Creating a K-W-L chart (see Activity 2) is another good warm-up option.
What will the students do?
Before beginning, have students "hinge" two mirrors using masking tape on the back or clear tape on the front. Once this is completed, students will observe the relationship between the angles of the two hinged mirrors and the number of images produced.
On a piece of paper or cardboard, have students mark angles of 180 degrees, 90 degrees, 60 degrees, 45 degrees, 36 degrees, 30 degrees and 20 degrees. Students will open the hinged mirrors to each of the specified angles and place an object (for example, a paper clip or a coin) between the two mirrors. Students will then count the number of images they see and record their data.
Afterwards, carry on a group discussion about what occurred. Explain that when you put an object between the two hinged mirrors, light from the object bounces back and forth between the mirrors before it reaches your eyes. An image is formed each time the light bounces off a mirror, and the number of images that you see in the mirrors depends on the angle that the mirrors form. As you make the angle between the mirrors smaller, the light bounces back and forth more times and you see more images.
Activity - A spoon is a good example of both a concave mirror and a convex mirror. Have students look at one side of a spoon and then write down in their science notebook what they see. For example, they might say that the reflection is upside down or right side up or that it is smaller or larger than their face. Then have them turn the spoon around and make the same observations regarding the other side. Explain to them that the side of the spoon that caves in is called a concave mirror, and the side that curves outward is called a convex mirror.
Writing - Have students create a science fiction story that addresses science facts about mirrors, reflection, or lenses, and includes strange and unusual happenings. For example, a student could create a tale about an alien that lands on Earth and sees its reflection for the first time when it lands near a clear pool of water. Or, a young person could find a "magic mirror" that shows what life was like at different eras in history. The variations are endless!
Reading - Read The Face in the Mirror (ISBN 0688153941) by Stephanie Tolan as a class or require students to read it on their own. The book for young adults blends Shakespeare, a ghost story, and life in the theater. It is about a 15-year-old boy who is sent to live with his father who works in the theater. An alternate book choice could be The Secret of Mirror Bay (ISBN 0448095491) by Carolyn Keene. The tale is a Nancy Drew mystery in which Nancy and her friends investigate reports of a mystery woman gliding over the water at Mirror Bay.
Historical Vignette: Caroline Herschel
Caroline Herschel was born in 1750 to a working class family in Germany. When she was ten she became sick with typhus. The disease stunted Herschel's growth, and she never grew past four feet three inches. Her father thought her condition made her unattractive and was sure that she would never marry. To her family, she could amount to nothing more than a housemaid, which she soon became.
After a few years of acting as a maid, Herschel went to live with her brother, William. He felt sorry for her and needed a housekeeper. William was a musician for some time, but had been progressively developing a love for astronomy. He desired to see into the depths of space and eventually did so by constructing powerful telescopes to aid his vision. After receiving a pension from King George III, William quit music to devote all of his time to making and selling telescopes. In time, Herschel began to help him in his business. She spent long hours grinding and polishing the mirrors they used to collect light from distant objects.
At the age of 32, Caroline Herschel became an apprentice to her brother. As she gained confidence, she became more and more of a help to William. Frequently when he would leave on business, Herschel would take over in his place. Visitors began to recognize her authority, and King George III gave her an annual pension of fifty pounds. This was the first time that a woman was formally recognized for a scientific position. While Herschel lived and worked with her brother, she discovered eight comets, which was a great accomplishment in the late 1700s. Herschel received the Gold Medal of Science for her life's work from the King of Prussia and became an honorary member of the Royal Astronomical Society and the Royal Irish Academy.
Writing - Have students imagine a letter that Caroline Herschel would have written to her brother after she took over his work. What kinds of things would Caroline write about? Would she discuss household matters? Would she want to share her latest news about looking for comets? As an extension to this, you could have students imagine that Caroline and William had e-mail and could communicate regularly. Have them think about how their correspondence would be different.
Artist Vignette: Leonard da Vinci
Leonardo da Vinci (1452-1519), known as a genius of the Renaissance, was an artist, inventor, engineer, theatre designer, and architect. He is also well known for keeping notebooks and sketchbooks, which continue to be used for study today. Da Vinci's notebooks are significant because he did not only record his observations of natural phenomena in them, but attempted to figure out how things work. To explain his work, da Vinci wrote long descriptions that included diagrams of his scientific and mechanical projects.
Da Vinci wrote in Italian using a special kind of shorthand that he invented himself. He also used "mirror writing" in his notebooks, a habit that has puzzled people for a long time. His notes started at the right side of the page and moved to the left. Only when he was writing something intended for other people to read did he write left to right. Contemporaries of da Vinci recorded that they saw him write and paint left-handed. He also made sketches showing his own left hand at work. Being a lefty was highly unusual in da Vinci's time. Because people were superstitious, children who naturally started using their left hands to write and draw were forced to use their right hands.
No one knows the true reason da Vinci used mirror writing, though several possibilities have been suggested. Some believe he was trying to make it harder for people to read his notes and steal his ideas, while others more specifically state that he was hiding his scientific ideas from the powerful Roman Catholic Church, whose teachings sometimes disagreed with what he observed. It has also been noted that writing left handed from left to right was messy because the ink just put down would smear as his hand moved across it. Thus, some argue that da Vinci chose to write in reverse because it prevented smudging.
Activity - Distribute paper and pencils and encourage students to try writing their signatures in cursive from right to left. If students have difficulty forming these letters in reverse, have them hold a pencil in each hand and write backwards with the usual writing hand while writing forwards with the opposite hand.
Have students write backward with pens and markers to make comparisons. Is one kind of writing tool easier to use this way than another? Distribute mirrors and show students how to position them to one side of their backwards writing to read it normally. A mirror also lets them check to see if they actually reversed all letters. Have students try writing reverse messages to a partner who can then decipher them with a mirror.
Discussion - In a follow-up discussion, ask students if the type of writing implement made a difference in the ease of mirror writing. You may also see if anyone is left handed in the class and whether it was easier or harder for them to do the mirror writing. Have students hypothesize why they think that da Vinci used this technique in his notebooks.
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