CTS Guide: Visible Light and Electromagnetic Radiation, pp. 194-195- Section IV Research Summaries
Reflection of Light and Mirrors
Most studies on children’s conception of light reflection were conducted in the 1980s and early 1990s, yet are still relevant today(AAAS 2009).
Students’ ideas about light reflection may be limited by the context in which they learned about the reflection of light. If their experiences have been mostly with mirrors, then students are apt to think that only things that are smooth or shiny like a mirror can reflect light (Driver et al. 1994).
When children were asked if moving their position would change the position of an image on a mirror, over half thought that it would. Ninety percent of the children thought that moving back from a mirror would allow them to see more of themselves in the mirror (Driver et al. 1994).
Mirrors are typically used in curriculum units on light to demonstrate characteristics of light reflection. Several studies have shown that students have difficulty understanding how an image forms on a plane mirror (Shapiro 1994).
Ramadas and Driver (1989) revealed that middle school students will accept the idea that mirrors reflect light but may not accept the idea that ordinary objects reflect light
A study by Anderson and Smith (1983) revealed that students could describe light as bouncing off mirrors but not off other objects. A few students even lacked a conception of light bouncing or reflecting off any objects.
Color
A study by Anderson and Smith (1983) found that 61% of the children they questioned thought color to be a property of an object without realizing that it results from light being reflected from the object.
Light and Shadows
Some researchers have found that children expect the shadow of an object to be the same shape as the object. Their predictions about shadows often refer to a shadow as a “reflection” or as a “dark reflection” on a screen (Driver et al. 1994).
Students seem to have more success in locating where an object’s shadow will fall in relation to a light source if the object is a person. They have more difficulty anticipating where a shadow will fall if it is a nonhuman object, such as a tree. Students who were able to anticipate where a shadow would fall and explain their ideas in terms of relative position of the light source, object, and the object’s shadow did so without including an explanation of the straight path of light in their explanation.
Connection Between Light and Sight
When drawing light rays to show how light travels to the eye, some students think the light ray is actually a material part of the light rather than a way to represent the light’s path (Galili and Hazan 2000).
The Harvard Smithsonian Center for Astrophysics Private Universe Project (1995) conducted interviews with children in the dark to find out if they believed they would see a red apple and a yellow and blue cube in a totally dark room and whether they would see the objects’ color. The students interviewed held persistently to the idea that if they waited long enough, their eyes would get large enough so that they would eventually see the objects.
A variety of alternative conceptual models are used by students to explain how we see an object. These models include (1) rays that go from an object to the eye, (2) the fact that light just helps us see better with no mention of how, (3) something goes from the eye to an object (eye as the activator of vision), (4) something goes back and forth between the eye and an object, (5) light goes from a source to the eye (and may include reflection) to help us see, (6) an image enters the eye, (7) a contrast with dark helps us see, and (8) sight goes further out when there is light (Driver et al. 1994).
Featherstonhaugh and Treagust (1990) found that many children assume we see not by light being reflected to our eye, but rather by looking, as if a visual ray emanated from the eye. They also found that many children think we can see in the dark. They found that this misconception was more prevalent among city dwellers than rural dwellers. Among both city and rural dwellers, 40% believed that cats could see in the dark.
Shapiro (1989) describes an interview in which a student describes light as being necessary to see a building because it illuminates it. However, the student did not connect the idea that light traveled from the building to the eye.
Piaget’s classic studies (1974) included young children’s ideas about light. He found that very young children often made no connection between an object and the eye.
Light Transmission
Students’ reasoning about how far light travels may rely on the intuitive rule “more A equals more B” described by Stavy and Tirosh (2000). In other words, students may believe a light more intense than a candle flame (such as from a lamp) travels further than light from a candle flame.
A study of 10th graders’ preinstruction ideas about how light travels from its source showed that students accept the idea of light spreading out from a source and then interacting with objects or materials on its way. However, the findings also indicated that the students had not developed a consistent descriptive and explanatory model of how light travels from a source. Light was sometimes shown as clinging around light sources and sometimes as emanating and extending far away from them. Directionality of light was rarely represented (Langley, Ronen, and Eylon 1997).
Difficulties in understanding how light travels contribute to students’ misconceptions about how light interacts with mirrors and how light must enter the eye in order to see an object (Driver et al. 1994).
One reason students have difficulty comprehending the path of light is because it is not visible (Ramadas and Driver 1989).
Studies of 10- and 11-year-old students show that they fail to recognize light as an entity that exists between its source and its effect and as something that travels. Two different conceptions were found to exist among students of that age: 1) light is equated with its source and 2) light as an entity located in the space between its source and effect (Guesne 1985).
Stead and Osborne (1980) used the example of a candle in the daytime and found that students did not think light traveled very
far from its source.