The focal length of a lens determines the magnification at which it images distant objects. It is equal to the distance between the image plane and a pinhole that images distant objects the same size as the lens in question.hen a lens is used to form an image of some object, the distance from the object to the lens u, the distance from the lens to the image v, and the focal length f are related by. The focal length of a thin lens can be easily measured by using it to form an image of a distant light source on a screen.
The Killing Fields (Khmer: áá¶ááá·áá¶á viel pi-kÊ°iet) are a number of sites in Cambodia where collectively more than a million people were killed and buried by the communist Khmer Rouge regime, during its rule of the country from 1975 to 1979, immediately after the end of the Cambodian Civil War (1970â1975).
One way that farms can control runoff is by planting cover crops when the fields do not have anything planted in them. A cover crop is a crop that is planted mostly during the winter when most other plants cannot grow. Farmers plant these crops to help stop soil erosion. Cover crops help stop erosion because these plants hold the soil in place with their roots, which means that wind or water cannot wash the soil away. Cover crops also help to increase the organic matter in soil, which increases soil health.