Students find the topic of geometric optics to be obscure and difficult (Galili & Hazan, 2000). Studies show students have learning difficulties with lenses in geometric optics (Galili, 1996; Galili, Bendall, & Goldberg, 1993; Galili & Hazan, 2000; Goldberg & Bendall, 1992; Goldberg & MacDermott, 1987). Galili, Bendall and Goldberg (1993) carried out a detailed research to investigate the knowledge about image formation of students in geometric optics. The twenty-seven students were enrolled in a section of an activity-based physics course designed for students preparing to teach in elementary school. The following topics were discussed in class: light and illumination, shadows and pinhole patterns of light, reflection and image formation by plane mirrors, refraction and distortion of objects viewed through transparent materials, and image formation by converging lenses. Students were interviewed indivually after they completed a unit. The findings showed that students had incomplete formal understanding of the process of image formation. The diagrams of students about image formation by a converging lens were incomplete representations. It was concluded that alternative instructional strategies and/or more instructional time might be needed to help students achieve a formal understanding of image formation. To overcome these learning difficulties, new learning materials and active learning environments should be developed. Active learning environments for students occur in an activity, in a group, in pairs, or alone. Students review and reflect upon the activity, and the teacher acts as a facilitator to encourage the students to apply their learning to their own situation (Anderson & De Silva, 2007). Research indicates students, who are actively involved in their learning tasks, enhance their retention of concepts (Cherney, 2008; Taraban, Box, Myers, Pollard & Bowen, 2007) and ensure better acquisition of scientific concepts than traditional instruction (Acar Sesen & Tarhan, 2011; Aydede & Matyar, 2009; Shieh, Chang &Tang, 2010; Taraban, Box, Myers, Pollard & Bowen, 2007). Designing an inquiry learning environment around how an optical system forms images may be an ideal method to overcome learning difficulties relating to optics’ concepts.

Students use their existing prior knowledge as a reference when constructing new information. So, primary and middle school education has an important place in science learning. Studies (Chang, 2001; Zoller & Pushkin, 2007) show traditional science learning practices are not effective to promote higher order cognitive skills. Constructing knowledge and effective learning requires active participation by the learners. The student-centered learning environment in which students actively engage hands-on activities supports a deeper knowledge (Marx et al., 2004; Singer, Marx, Krajcik, & Chambers, 2000). Also studies report that such hands-on activities attract students’ interest and enhance their motivation (Holstermann, Grube, & Bögeholz, 2010; Tuan, Chin, Tsai, & Cheng, 2005; Wen-jin, Chia-ju, & Shi-an, 2012 ). For example; Wen-jin, Chia-ju, and Shi-an (2012) investigated the effect different hands-on activities on female students’ learning motivation towards science. Five hundred female students filled out the learning motivation scale before and after exercising hands-on activities. The results showed that all types of hands-on activities in this study could promote female students’ learning motivation towards science. Also, hands-on activities about daily life issues could better promote female students’ learning motivation toward science than the others. Hence, in the following it is suggested an active instructional application, involving a series of simple and inexpensive hands-on activities is needed to learn about optical lenses at the middle school level. With this step-by-step active learning environment, it is thought that students would distinguish the two types of lenses during the first step. The students will learn properties of converging and diverging lenses in the second step. They will observe application of optical lenses to cure eye defects in the third step. Finally, they will explore image formation via making a refracting telescope.

The present paper aimed to present a guide for middle school teachers to teach lenses in geometric optics via active learning environment including low cost hands-on activities.

Optical lenses in life

The optical lenses in human eye

Lenses of the eye are thicker in the center than at the edges. Therefore, they are positive and converging, and form a real, inverted image on the retina. The image on the retina is formed by two lenses: the cornea and the crystalline lens (Levine, 2001). The cornea is responsible for two-thirds of the focusing, and the crystalline lens does the fine focusing. Light rays are refracted by the cornea and the crystalline lens. The image is formed on the retina and is upside down or inverted. Visual cortex in the brain inverts the image back to normal (Maheshwari & Williams, 2001).

The optical lenses for eye defects

The optical lenses are widely used in the correction of eye defects. One of the common eye defect is myopia (near-sightedness). Myopia is inability of the eye to see a distant object. A myopic eye has more than necessary refracting power and so light rays from a distant object focus in front of the retina. Diverging lens is used for the cure of myopia as to refocus light rays from far distances onto the retina (Maheshwari & Williams, 2001). Another common eye defect is hyperopia (far-sightedness). Hyperopia is inability of the eye to see a nearby object. The hyperopic eye has too little converging power than necessary and the images of nearby objects are focused at a location behind the retina. Converging lens is used for the cure of hyperopia to move the hyperopic near and far points inward (Maheshwari & Williams, 2001).

The optical lenses in instruments

The optical lenses are used in many instruments as camera, projector, microscope, telescope, binoculars and etc. in our life. Students will be more interested in this physics topic if they discover optical lenses have wide application field in daily life. So below activities as refraction of light by lens in our eye, using of optical lenses to cure eye defects, refraction of light in a camera and making a refracting telescope will draw students’ attention.