Mouth decision one: "a focal (point) points virtual and solid, two focal (distance) points size; Virtual image is positive on the same side; The real image is turned on its side, and the far image becomes smaller." Mouth decision two: the object far real image is small and close, the object near the real image is large and far, if the object is placed in the focus, the virtual image is amplified; The slide image is so big, the object is between one and two focal points, the camera shrinks you smaller, the object is twice the focal distance.
The propagation of sound requires a medium, a vacuum can not transmit sound (1) sound depends on all gases, liquids, solids as a medium to spread out, these as a medium called the medium.
Sound is produced by the vibration of the object, but not all vibrations will emit sound between sound transmission sound transmission needs a medium, vacuum can not transmit sound (1) sound to rely on all gases, liquids, solids as a medium to spread out, these as a medium called the medium.
The second chapter "Light phenomenon" review outline the linear propagation of light source: definition: objects that can emit light are called light sources. Categories: Natural light sources, such as the sun, fireflies; Artificial light sources, such as bonfires, candles, oil lamps, electric lights. The moon itself does not shine, it is not a source of light. Rule: Light is in the same uniform medium