F.3 Physics 唔明 pls help :D

1. If the angle of dispersion is wide, then only a single coloured light from the spectrum is at a suitable angle t your eyes that enables you to see it. Other coloured lights are dispersed at different angles that are not caught by your eyes.

2. You see an object appears RED because it only reflects RED light. Likewise, you see an object blue becuase it only reflects blue light, and so on.

Thus, when other coloured lights shine on a red object, all these coloured lights are absorbed (i.e. not reflected). In the absence of any reflected light, you cannot see the object. It appears black to you.

3. I suppose you refer to the visible range in the electromagnetic spectrum. In the visible spectrum, violet and blue are at the high frequency end, wereas red is at the low frequency end. The different frequencies are seen by human eyes as different colours.

4. This depends on the locations of the image formed from the lens. If the image is formed behind and close to the convex lens, it size is small. On the other hand, if the image is formed farther away from the convex lens, its size is large.

The reson is simple. Image is formed by intersection of light rays after refraction from the lens. If the point of intersection is farther away from the lens, the intersection point must also be far away from the principal axis, thus producing a large size image.


2011-11-18 13:56:07 補充：
Your suppl question:
Magnifying glass is a convex lens. The image formed by distant object is a real image and is formed behind the mirror (at the same side as your eye). Any image formed by lenses not on the same side of the object must be inverted.

2. 所謂既red object 即係一件物件會reflect red light，其他顏色係reflect 唔到，而green light 無紅光，咁照落去，無紅光反射，而綠光反射唔到，咁所以就會無光反射，blue object 理同上。

4. Convex lens 其實唔係一時produce 大image 同細image，佢一直都係只會produce大image唔會produce 細image，所謂大image其實係我地既錯覺，大image係因為個object比focus point更接近個convex lens因此光會散開，咁我地會自動地將所有散開既光延伸出去後聚焦個點當成我地睇到既野，而延伸出去既係大D所以就有大image，其實同concave lens 係差唔多，concave lens都係因為錯覺所以先會有小image 既出現。