physics - convex lens

Q1.我知點畫虛線，但唔明點解要畫

虛線係指個d虛擬的影像,or 光線,因為係physics畫圖的技巧中,個rule本身就係實線就係實像 or 光線,虛線就指虛擬的影像,or 光線。

例如你畫個正立,放大ge虛像,,為咗識別由object 經過lens的2條光線,於是e 2條光線就係實線,跟住由2條實線後面伸展落去個2條就係虛擬的,現實上跟住唔存在的,因為個2條係基於人眼睇野係直線的原因,咁我地才畫出來,咁就可以係個畫圖explain得好d。

比如mirage為例,我諗你都知全內反射啦(total internal reflection),係沙漠,光線由高至低,跟住全內反射,去返上去到人眼到,跟住我地就會拿虛線從人眼個度畫落地下到,咁係因為現實中根本就無e d咁的光線,係虛擬的,e個同樣想指明,人睇野係直線,so才會有mirage的出現。

Q2.虛像同實像有咩唔同
當虛線係指光線個時你就明啦。但當虛線係拿來畫個image個時,我地就會話個image係virtual(虛像),相反,實線就係實像(real image)

係convex lens,當u > f,個image就係實線,因為你見到個2條由object出發,經過個lens,跟住focus係1個point的個2條光線係現實上真係focus咗係一個point,咁話到明現實上,姐係話係現實上個image係真係存在。
另外一個更specific的說法就係,實像係可以被screen capture到的,好似你上堂個時的投影機咁,個投影機其實就係拿convex lens,將個image投射到個screen到,咁e個就係一個實像。
相反,虛像就唔可以被screen capture到,因為個image現實上根本唔存在,只係你認為佢存在姐。
convex lens裡面,當u<f個時,現實上根本無image formed 到,因為個2條光線都無focus到, 但因為人係直線睇野,於是個光線係人的angle來睇,個image focus咗,咁就有咗個image,其實根本無咁的image,只係你諗出來姐。
同樣地, 虛像係唔可以被screen capture到。你諗下,你睇住鏡裡面的你,你可唔可以拿一個screen,令到個image係個screen到,好似投影機投射image咁?當然唔可以啦,因為佢根本係一個虛像來。係convex lens個時,你睇下你可唔可以將個放大的image focus係個screen到?答案都係一樣,唔可以!

其實總括來說,虛像係cannot be captured by screen
實像就可以被screen capture到
去到test,exam你咁答基本上就可以拿曬分

Q1.我知點畫虛線，但唔明點解要畫
The dotted lines are not real light rays. They are used to locate the position of the image from where the light rays are observed by our eyes as if they are coming from. In other words, the dotted lines can be regarded as the "virtual light rays" that come from a virtual image.

Q2.虛像同實像有咩唔同
Real image are formed by actual intersection of light rays after passing through the lens. Hence, it can be formed on a screen.
Virtual image are formed by producing the light rays backward as if the rays are coming from the image. Since the light rays do not actually meet, a virtual image cannot be formed on a screen.

Following from the above results, since a conves lens converges light rays after passing through it, a real image must be formed on the other side of the lens opposite to that where the object is placed. It must be inverted.
A virtual image must be formed on the same side of the object. It must be erected.