光學-有關折射

1.
假設o個個人的眼去到個頭的length 係AC
o個個人的眼去到隻foot係CE
佢個頭o個度有光線去到鏡的最頂點,跟住反射落隻眼到
係中間加返條normal,state 個angle i 同 angle r
根據law of reflection,
angle i = angle r
normal係common line
normal同o個個人都係90度
咁e個就係一個同等三角形 (ASA)
咁假設normal同o個個人的交點係B點
咁AB = BC
同樣地
個foot o個度有光線去到鏡的最底點,跟住反射落隻眼到
好似上面咁,
normal同o個個人的交點係D點
咁CD = DE
鏡的length係BC + CD = (AC - AB) + (CE - DE)
= (AC + CE) - (AB + DE)
= 2a - (AC + CE) / 2
= 2a - 2a /2
= a
答案就係 C

2.咁因為我唔知你轉咗幾度,我就假設係a度

原本個angle of incidence = angle of reflection = 0度
跟住轉咗a度,
於是鏡片同個incident ray之間個angle就係90 - a 度
咁因為normal 同鏡係90度angle
個angle of incidence 就係90 - (90 - a) = a度
by law of reflection, angle of reflection = a度
咁佢係想問原本個reflected ray 轉咗幾多度angle同
原本reflected ray係同normal同incident ray同一條線來
e家個incident ray 係無變過,so e家個reflected ray 同 incident ray 係2a 度angle

我估你原本係話想轉15度angle
咁答案應該就係C

但如果係7.5度angle
咁答案就係A

唔明的話我sd個圖比你睇下

1. Use similar triagnles.
The image, the mirror and the eye of the pupil formed two similar triangles. Since the distance from the eye to the mirror is equal to half the distance from the eye to the image (Laws of Reflection), the mirror height is therefore equals to half of the image height, which is the same as the height of the pupil ( i.e. 2a).

The mirror is thus of height a.

2. The reflected ray rotates at an angle twice of the angle which the mirror rotates, and at the same direction of rotation as the mirror.

Thus, if the mirror rotates 15 defrees clockwise, the reflected ray will rotate 30 degrees clockwise.

Proof could be done by simple geometry in drawing out the incident ray and the normal, before and after the rotation.

1. B, BECAUSE object height/2 is the minimum height of the mirror to see the whole image..

2.I DON'T KNOW BECUASE 順時針方向轉動 HOW MANY DEGREE?

2009-12-30 18:22:15 補充：
BUT REFLECTED ANGLE =INCIDENT ANGLE

2009-12-30 18:23:30 補充：
1 IS D. I FORGOT THE HEIGHT IS 2a, sorry~~