Summary of physical knowledge

This paper will introduce some physical knowledge, including glasses, microscope, camera and so on.

Focal length and apparent distance of glasses

The apparent distance of normal eyes is 20cm, while nearsighted people often make the paper closer to their eyes when writing, because the apparent distance of myopia is less than 20cm. The reading of a pair of nearsighted glasses is 200 degrees and the focal length is 2m.

A small mirror of a microscope

A small mirror under a microscope is used to reflect light. It can be a flat mirror or a concave mirror.

Camera lens and film

The lens of a camera is equivalent to a convex lens, and the film is equivalent to an imaging screen. When taking pictures, the distance from things to the lens should be more than twice the focal length.

Slide of slide projector

Slide projectors use convex lenses to form inverted stereoscopic images. In order to see the "upright" image, slides should be inserted backwards on the shelf.

Exploring convex lens imaging

When exploring convex lens imaging, in order to make the image of candle flame in the middle of light screen, it is necessary to adjust the height of candle flame convex lens and light screen at the same time.

Use of magnifying glass

When reading a newspaper with a magnifying glass, grandma should keep the newspaper and eyes still so as to see bigger and clearer words. The magnifying glass should be closer to the newspaper.

Imaging of goldfish bowl

Through the bulging goldfish bowl, we can see that the goldfish is bigger than the actual goldfish. This is because the goldfish bowl filled with water is equivalent to a convex lens, and what we see is the virtual image of goldfish.

Adjustment of microscope

When a doctor uses a microscope to test a sample, he always turns the knob on the microscope to adjust the distance between the objective lens and the eyepiece to make the image clearer.

Camera shooting

Xiaoying wants to take a 2-inch photo after taking a 1 inch photo. Photographers should keep the camera close to people and lengthen the camera box.