Lab 2: The hand lens and the microscope
To study the structure of living things we need magnifying instruments. The simplest is the hand lens: a lens bulging on both sides that magnifies an object about 2–20 times. With it you can notice the round cells in the flesh of a watermelon or tomato. A microscope is a laboratory instrument that shows even smaller objects. Its stand carries the tube and the stage. At the top of the tube is the eyepiece (ocular) and at the bottom the objective; both are magnifying lenses. The coarse-focus screw raises and lowers the tube, the fine-focus screw makes the image sharp. Under the stage is a mirror that directs light onto the specimen (modern microscopes often have a built-in lamp), and a clip holds the specimen in place. The magnification of a microscope equals the eyepiece number times the objective number: eyepiece 10, objective 20 gives 10 × 20 = 200 times. The specimen is viewed first with the small objective and then with the large one, the microscope is not moved while you work, and the image is drawn in the notebook.
Teacher-led: label the nine parts on a picture of the microscope (eyepiece, coarse screw, fine screw, stand, stage, mirror, clip, objective, tube). Then, with the teacher, look at a ready-made specimen with the small objective and draw it. Safety: the microscope is taken only with the teacher’s permission and carried with two hands; never point the mirror straight at the sun, which can damage the eyes; do not touch the lenses with your fingers.