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300 / visible region

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geometrical optics physical optics.

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Reflection of light

:
Reflection: Image formation by mirrors

. 90% .


Reflection Law
angle of incidence qi . angle of reflection qr . .


qi = qr



Image formation by plane (flat) mirror
:


virtual image .

plane (flat) mirror :
upright
( )
virtual
do di.

Image formation by spherical mirror
ɡ convex mirror concave mirror.
convex mirror concave mirror .i

Focal length of spherical mirror
concave mirror focus point F A focal length f.


principal axis ǡ center of curvature C raduis of curvature r

. f r.


B F. CB r ( ) CB B CBF CF FB FB FA FA f CA 2FA

r = 2f

r ( ).



(1)
:
(1) ( ).
(2) ( ).
(3) C ( ).
I .
.
(2)
.
(3)
f r .
(4)
.
(5)
f ɡ .


convex mirror. f C :


convex mirror




convex mirror
Mirror equation
.

do di f.


do do :
A .



ABV DCV


ABF D'VF .
do .


Mirror equation

f = focal length (m)
do = distance from mirror to object (m)
di= distance from mirror to image (m)

Magnification
m hi ho .

hi/ho di/do


. :

hi = ****** of the image (m)
ho = ****** of object (m)
m = magnification (how many times bigger or smaller)


Sign convention for mirrors
do di real virtual upright inverted :

do+ real objectdo- virtual objectdi+ real imagedi- virtual image

f r
r & f+ concave mirrorr & f- convex mirror

M
M+ uprightM- inverted


Example 1
A 1.5 cm high diamond ring is placed 20 cm from a concave mirror whose radius of curvature is 30 cm. Determine (a) the position of the image, and (b) its size.

Solution
(a)

f=r/2
1/di di
di

(b)


hi = m ho = -3 x 1.5 = -4.5cm

Example 2
A 1cm high object is placed 10cm from a concave mirror whose raduis of curvature is 30cm. (a) Draw a ray diagram to locate the position of the image. (b) Determine the position of the image and the magnification analytically.

Solution
(a)

.

(b)



.




Example 3
A convex rearview car mirror has a radius of curvature of 40 cm. Determine the ******** of the image and its magnification for an object 10m from the mirror.

Solution
:

40/2 f=r/2

f=r/2=-40/2 =-20cm






19.6cm .


.
Example 4
A convex mirror has a radius of 20 cm. An object is placed 30 cm in front of the mirror. Determine where the image will appear.

Since the radius is 20 cm (which is the distance from the mirror to the centre), and since the focal point is half ways in between and negative for a convex mirror,
f = -10 cm.


Since di is negative, it appears behind the mirror as a virtual image.
Example 5
For the same situation from Example 4, determine how tall the image is if the object is 5.0cm tall. Also determine the magnification.