Light tugas fisika

8/2/2019 Light tugas fisika

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• What do you feel if there is no light?

• Can you see an object around you?

Let’s look next slide



pelindung orang-orang yang beriman. Dia

mengeluarkan mereka dari kegelapan menuju

cahaya.(QS 2:257)



LIGHTCAHAYA

NUR



Indicators

You are able to :

• Design experiment to study about the

direction of light travel. – By using OHP or candle to make shadow(s)

• Observ form of shadow, to explain light

characteristic(s,k)

• Make deffer betwen shadow and image





• Light spread out from light sources toall direction.



Light source is dot



Source of light like dot



CONCLUSION

• When something block a light, wewill see a shadow.



Shadow (bayang-bayang)



CONCLUSION• A wayang playing and making shadow

are of phenomena suggest that lighttravels in straight lines.

• Light travels in straight line in vacuum or uniform medium.

• In drawing illustrating the paths of

straight line it is use light rays



CONCLUSION• Seeing is actually a rather passive

activity.

• What you see depends on the light thatenters your eyes and not on somemysterious rays that leave them.

• In fact, light passing through clean air is

invisible.



CARACTERISTIC OF LIGHT

1. Have velocity 300.000.000 m/s

2. Part of solar system spectrum

3. An electromagnetic wave

4. Travels in straight line

5. Can be reflection6. Can be refraction

7. Can be dispersion



We are going to learn three kind

of LIGHT

•Reflection

•Refraction

•Dispersion



LIGHT

REFLECTION REFRACTION DISPERSION

PLANE MIRROR CONCAVE MIRROR CONVEEX MIRROR CORVERGING LENS DIVERGING LENS



Shadow and Image

• Shadow (bayang-bayang) is dark area

on the back of object

• Image (bayangan) is light area, it is the

area that the light come together



Moon eclipse diagram

Umbra

Penumbra





Shadow can devided in two part

• Umbra : The darkest region is where all of

the shadow overlap.

• Penumbra : The darkest region is whereonly some of the shadow overlap.



REFLECTION OF LIGHT

Diffuse reflection

Regular reflection



Activity

• Do activity page 265

• To investigation the relation between te

angle of incidence and the angle of reflection

• To find out the characteristic of mirror

plane image



The reflection of light on a plane mirror

Incidence ray normal line reflected ray

x x

The incidence angle the reflected angle



THE LAW OF REFLECTION

• The incident ray, the reflected ray and thenormal surface at the point of incident all lieon the same plane.

• The angle of incidence is equal to the angleof reflection.



Pemantulan pada Cermin Datar

Sifat bayangan Cermin datar•

Sama besar dengan bendanya• Jarak bayangan = jarak benda

• Posisi bayangan tertukar



Pembentukan bayangan pada cermin datar

Jarak benda = jarak bayangan



Susunan dua buah cermin datar

• Susunan dua buah cermin datar akan

menghasilkan jumlah bayangan yang lebih

dari satu, hal tersebut tergantung besarsudut antara dua cermin datar tersebut.

• Bagaimanakah hubungan antara jumlahbayangan dan besarnya sudut ?



Sudut dua cermin 90o

Hitung banyaknya bayangan yang terbentuk ?



Pematulan pada Cermin cekung

Sifat-sifat Cermin Cekung

1.Permukaan cermin melengkung ke dalam

2.Mengumpulkan berkas sinar

3.Digunakan pada lampu senter, lampu mobil

dll.



PEMBENTUKAN BAYANGAN PADA CERMIN

CEKUNG

Tiga berkas sinar istimewa

1. Sinar datang sejajar sumbu utama

dipantulkan menuju titik fokus (F)2. Sinar datang melelui titik fokus (F)

dipantulkan sejajar sumbu utama

3. Sinar datang yang melalui pusatkelengkungan, dipantulkan kembalimelalui pusat kelengkungan (M)



Sumbu utamaM F O

TIGA BERKAS SINAR ISTIMEWA



Sumbu utamaM F O




Sumbu utamaM F O

PEMBENTUKAN BAYANGAN PADA CERMIN CEKUNG

Bayangan diperkecil, terbalik dan nyata



Sumbu utamaM F O

Bayangan diperbesar, terbalik dan nyata



Sumbu utamaM F O

Bayangan diperbesar, tegak dan maya



Sumbu utamaM F O

Tidak terbentuk bayangan



Sumbu utamaM F O

Bayangan sama besar, terbalik dan nyata



An equation can also be used to located the

image and find its size. The focal length (f) thedistance of the object from the mirror (S0) and

the distance of the image from the mirror (S1)

are related by the mirror equation :

10

111SS f



The ratio of the size of the image (h1) to the size of

the object (h0) is called the magnification (m). Themagnification is related to the distances to the mirror

by equation :

0

1

0

1

S

S

h

hm

If S1 and S0 positive, the both m and h1 are

negative. This means that the image is

inverted.



PEMBENTUKAN BAYANGAN PADA CERMIN CEMBUNG

Tiga berkas sinar istimewa

1. Sinar datang sejajar sumbu utama dipantulkan

seolah-olah berasal dari titik fokus (F)2. Sinar datang menuju titik fokus (F) dipantulkan

sejajar sumbu utama

3. Sinar datang menuju pusat kelengkungan

cermin, dipantulkan kembali seolah-olah berasal

dari pusat kelengkungan (M)




Sumbu utamaF O F




Sumbu utamaF O F



Sumbu utamaM O F

PEMBENTUKAN BAYANGAN PADA CERMIN CEMBUNG



Sumbu utamaM O F



Sumbu utamaM O F



EXERCISE :

1. An object is 15 cm from a spherical

concave mirror having a 20 cm radius.

Locate the image by means of :a. a ray diagram

b. the mirror equation



Solution :

a.

f f OM 10

20

10



b. Known : R = 20 cm

f = ½ R = ½ x 20 = 10 cm

S0 = 15 cmAsk : S1……………………..?

Solution :

1/S1 = 1/f - 1/S0

= 1/10 – 1/15 = 3/30 – 2/30

= 1/30

S1 = 30 cm



2. An object 15 cm in height is 12 cm from 1 sphericalmirror having a 12 cm radius. Locate the image by

means of :a. a ray diagram

b. the mirror equation

c. what is the height of the image

3. An object is located so that a virtual image is formed24 cm behind a concave mirror that has an 8 cm focallength.

a. calculate the object distance

b. if the image is 12 cm, what is the size of theobject?

Light tugas fisika

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