Concave Mirror

Mirror By : Aries Triwidajati Soenoko SMP Negeri 2 Cileunyi

Basic Competence Investigate the characteristic of light and the relation with mirror and lens

Learning Objectives After this lesson, student are able to : 2. Drawing of an image through a ruler in the mirror 3. Mention the characteristics of an image in the mirror 4. Calculate focus, object, image, and magnification positions.

Concave Mirror Characteristic of concave mirror 2. Concave mirror is part of the inner surface of a hollow sphere 3. Concave mirror product converge ray 4. CM in daily life is used to collect ray, such as : solar panel,

Reflection of light in CM

M

F

O

Principal axis

Part of CM M is geometric center (pusat lingkaran) R is the sphere radius (jari-jari) A is the center of mirror (pusat cermin) MA is the principal axis (sumbu utama) F is the focal point of the mirror (focus) FA is the focal lengt (jarak focus) The focal length is half the distance between the mirror and the center of curvature M.

M

F

O

Sumbu utama

Real image Paralel ray of the sun aor other object are reflected from a concave mirror at the focal point (F) of mirror The focal point become bright on the paper, it is called image of the sun An image is real image if rays actualy converge and pass trough the image A real image can be seen on a piece of paper or screen.

Virtual image A virtual image cannot be seen on a piece of paper or screen because, light rays do noot converge at virtual image. Image of plan mirror is example of virtual image.

Drawing image on Concave mirror Using three kind of rays 2. The ray parallel of principle axis is reflected through the focal point (F) 3. The ray passing trough F is reflected parallel to the principle axis 4. The ray passing trough the center of curvature C is reflected along its same path through C

Three kind of rays

M

F

O

Sumbu utama

Making image

M

Inverted, virtual, smaller

F

O

Sumbu utama

M

Inverted, virtual, bigger

F

O

Sumbu utama

M

Upright, virtual, bigger

F

O

Sumbu utama

M

F

Tidak terbentuk bayangan

O

Sumbu utama

M

Reverse, virtual, equal

F

O

Sumbu utama

Making image

III

II

I M

IV F

O

Bayangan diperkecil, terbalik dan nyata

Principle axis

Making image

M

F

O

Bayangan diperkecil, terbalik dan nyata

Sumbu utama

M

F

O

Bayangan diperbesar, terbalik dan nyata

Sumbu utama

M

F

O

Bayangan diperbesar, tegak dan maya

Sumbu utama

RESUME

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Convex Mirror Characteristic of convex mirror 2. Convex mirror is part of the outer surface of a hollow sphere 3. Convex mirror product diverge ray 4. Convex mirror does not form real image 5. Convex mirror in daily life is used in car, and its is used in stores to observe shoppers. 6. Focal point (f) is placed behind mirror (the focal length is a negative number)

A

F

M

Sumbu utama

A Principle axis

F

M

Three kind of light

A

F

M Sumbu utama

Making image in convex mirror Three kind of ray 2. The ray parallel to the principal axis is reflected as if it is from focal point (f) 3. The ray to focal point is reflected parallel to the principal axis 4. The ray to the center of curvature M is reflected along its same path through M

Making image in convex mirror

A

F

M

Sumbu utama

A

F

M

Sumbu utama

A

F

M

Sumbu utama

An equation can also be used to located the image and find its size. The focal length (f) the distance of the object from the mirror (S0) and the distance of the image from the mirror (S1) are related by the mirror equation :

The ratio of the size of the image (hi) to the size of the object (h0) is called the magnification (m). The magnification is related to the distances to the mirror by equation :

If Si and S0 positive, the both m and hi are negative. This means that the image is inverted.

Resume f always negative (-) Convex mirror always form virtual image, smaller and upright The object always on the 4th room

Characteristics of Focus of a Concave and a Convex Mirror

Review 1. A concave mirror has a radius of curvature of 60 cm. Calculate the image position and magnification of an object placed in front of the mirror at distances of (a) 90 cm and (b) 20 cm. (c) Draw ray diagrams to obtain the image in each case. 2. Calculate the image position and magnification for an object placed (a) 20 cm and (b) 60 cm in front of a convex mirror of focal length 40 cm. (c) Use ray diagrams to locate image positions corresponding to the object positions in (a) and (b).

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