# What are cones of light in physics

## Understand physics 4, textbook

7 The world of the visible  Learning objective check 1, page 84 3. How can the path of light rays become visible? Light and fog (Fig. 7.1) Darken the room. Use the fog machine to create the largest possible swaths. Shine through the fog with a slit lamp. What do you see At V3, the light beam is perceived by the eye because the fog droplets reflect the light. The light becomes visible in this way. Finely distributed dust can also be seen in the room air when many rays of light shine into the room, for example between curtains. The path of the light rays from car headlights is very clearly visible in the fog. M The course of light rays can become visible through reflection on dust particles or water droplets or when shining along objects. 4. How does light spread? On all sides (Fig. 7.2) Cut off the upper part of a beverage carton and make many small holes in the side walls and the bottom with a graver. Then put the box over an 18 W halogen light bulb. The room is darkened. Dense swaths are created with the fog machine. How do the rays of light spread? Through the clouds of fog (V4), the spread of the light rays can be clearly seen in all directions. Since, for example, the light of the room lighting is seen by everyone in the room, you can also conclude from this that the light spreads in all directions (Fig. 7.3). Nothing is faster than light. The speed of light is about 300,000km / s. The Danish astronomer Ole Römer (1644–1710) was the first to establish this in a rough approximation in 1676. The Dutch astronomer, mathematician and physicist Christiaan Huygens calculated the speed of light for the first time in 1678 at 212,000 km / s. 1 light year is what we call the distance that light travels in one year. There are around 10 trillion (= 10 12) km. M light spreads in a straight line to all sides from every point of a luminous body. The speed of light is around 300,000 km / s. V3 V4 7.4 The lighting of a castle wall shows the spread of light. 7.2 On all sides 7.1 Light and fog 7.5 Sunset 7.6 Spotlights illuminate the musicians at a concert. Pinhole diaphragms 7.3 Light propagates in a straight line from every point of a luminous body. For testing purposes only - property of the publisher öbv