Latihan Soal Cermin Dan Lensa

1.

Sebuah lensa cekung memiliki jarak fokus 20 cm. apabila sebuah benda diletakan 30 cm di depan lensa, maka jarak bayangan yang terbentuk dari lensa adalah....

A.

12 cm di depan lensa
B.

12 cm di belakang lensa
C.

15 cm di depan lensa
D.

15 cm di belakang lensa

Correct Answer
B. 12 cm di belakang lensa

Explanation
When an object is placed in front of a concave lens, the image formed is virtual, erect, and diminished. The distance of the image from the lens is negative, indicating that the image is formed on the same side as the object. In this case, the object is placed 30 cm in front of the lens, and since the image is formed 12 cm behind the lens, it means the image is located on the same side as the object but closer to the lens. Therefore, the correct answer is "12 cm di belakang lensa."

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2.

Cermin cekung berjari-jari 100 cm, di depannya diletakkan benda berjarak 80 cm. sifat bayangan benda yang terbentuk adalah....

A.

Nyata, terbalik, dan diperbesar
B.

Nyata, terbalik, dan diperkecil
C.

Nyata, terbalik, dan sama besar
D.

Maya, tegak, dan diperbesar

Correct Answer
A. Nyata, terbalik, dan diperbesar

Explanation
The correct answer is "nyata, terbalik, dan diperbesar". When an object is placed in front of a concave mirror, a real image is formed. The image is inverted or terbalik, meaning it is upside down compared to the object. Additionally, the image is magnified or diperbesar, meaning it appears larger than the actual object. Therefore, the correct answer is "nyata, terbalik, dan diperbesar".

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3.

Suatu lensa cembung memiliki jarak titik fokus 0.2 m. Bila suatu obyek berada pada jarak 0.4 m. Perbesaran bayangan benda tersebut adalah....

A.

4
B.

3
C.

2
D.

1

Correct Answer
D. 1

Explanation
The magnification of an image formed by a convex lens can be calculated using the formula: magnification = image distance / object distance. In this case, the object distance is 0.4 m and the image distance is 0.2 m (since the focal length is 0.2 m). Plugging these values into the formula, we get magnification = 0.2 / 0.4 = 0.5. Therefore, the magnification of the image is 0.5, which corresponds to the answer choice 1.

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4.

Suatu obyek diletakkan di depan lensa cekung pada jarak 40 cm. Bayangan yang terbentuk berupa bayangan tegak dengan ukuran 1/2 dari ukuran obyek. Berapakah jarak titik fokus lensa cekung tersebut ?

A.

40 cm
B.

30 cm
C.

20 cm
D.

10 cm

Correct Answer
A. 40 cm

Explanation
The given question states that an object is placed in front of a concave lens at a distance of 40 cm. The resulting image is upright and has a size that is half of the object's size. The question is asking for the focal length of the concave lens. According to the lens formula, the focal length (f) is equal to the distance between the object (u) and the image (v), which is 40 cm in this case. Therefore, the correct answer is 40 cm.

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5.

Sebuah benda dengan tinggi 10 cm berada pada jarak 12 cm dari lensa cembung dan jarak fokus 18 cm. Tinggi bayangan benda adalah ...

A.

40 cm
B.

30 cm
C.

20 cm
D.

10 cm

Correct Answer
B. 30 cm

Explanation
The height of the image can be determined using the lens formula, which states that 1/f = 1/v - 1/u, where f is the focal length of the lens, v is the image distance, and u is the object distance. In this case, the object distance is given as 12 cm and the focal length is given as 18 cm. Plugging these values into the formula, we can solve for v, which represents the image distance. After calculating, we find that v = 36 cm. Since the height of the object is 10 cm, the height of the image is given by the magnification formula: h'/h = -v/u, where h' is the height of the image and h is the height of the object. Plugging in the values, we find h' = -v/u * h = -36/12 * 10 = -30 cm. However, since the height cannot be negative, the height of the image is 30 cm.

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6.

Sebuah benda diletakkan di depan cermin cekung cekung yang memiliki jarak fokus 15 cm . Agar bayangan yang terbentuk tiga kali lebih besar dan nyata , maka benda harus diletakkan di depan cermin sejauh ...

A.

5 cm
B.

10 cm
C.

15 cm
D.

20 cm

Correct Answer
D. 20 cm

Explanation
To obtain a magnified and real image, the object must be placed beyond the focal point of a concave mirror. In this case, since the focal length is 15 cm, the object should be placed at a distance greater than 15 cm from the mirror. The question states that the image should be three times larger, indicating a magnification factor of 3. According to the mirror formula, the magnification is equal to the ratio of the image distance to the object distance. Therefore, the object distance should be three times the image distance. As the image distance is 20 cm, the object distance should be 3 times that, which is 60 cm. Thus, the object should be placed in front of the mirror at a distance of 60 cm - 15 cm (focal length) = 45 cm.

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7.

Pelangi merupakan salah satu peristiwa yang menunjukkan bahwa cahaya memiliki sifat ....

A.

Cahaya tampak
B.

Cahaya merambat lurus
C.

Cahaya dipantulkan
D.

Cahaya dibiaskan

Correct Answer
D. Cahaya dibiaskan

Explanation
Pelangi merupakan salah satu peristiwa yang terjadi ketika cahaya matahari melewati tetesan air di udara dan mengalami pembiasan. Pembiasan adalah sifat cahaya yang menyebabkan cahaya berbelok atau berubah arah saat melewati medium yang berbeda, seperti udara dan air. Oleh karena itu, jawaban yang tepat adalah "Cahaya dibiaskan".

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8.

Sebuah benda diletakkan 15 cm didepan cermin cembung berjari-jari 20 cm. Jarak dan sifat bayangannya adalah….

A.

15 cm, tegak
B.

10 cm, tegak.
C.

6 cm, tegak.
D.

16 cm, terbalik.

Correct Answer
C. 6 cm, tegak.

Explanation
The correct answer is 6 cm, tegak. When an object is placed in front of a convex mirror, the image formed is always virtual, upright, and diminished in size. The distance of the image from the mirror is determined by the equation 1/f = 1/v - 1/u, where f is the focal length of the mirror, v is the distance of the image from the mirror, and u is the distance of the object from the mirror. In this case, the object is placed 15 cm in front of the mirror, which is greater than the focal length of 20 cm. Therefore, the image is formed on the same side as the object, 6 cm from the mirror, and is upright.

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9.

Perhatikan gambar berikut!Jika bayangan yang terbentuk adalah tegak dan diperbesar 4 kali, maka letak benda adalah….cm dari depan lensa.

A.

6
B.

8
C.

12
D.

18

Correct Answer
D. 18

Explanation
Jika bayangan yang terbentuk adalah tegak dan diperbesar 4 kali, ini menunjukkan bahwa lensa yang digunakan adalah lensa pembesar (konvergen). Dalam lensa pembesar, letak benda berada di antara fokus dan lensa. Karena bayangan yang terbentuk diperbesar, berarti letak benda harus lebih dekat dengan lensa daripada fokus. Pada lensa pembesar, perbandingan antara letak benda dan letak bayangan adalah sama dengan perbandingan antara besarnya bayangan dan benda. Jadi, jika bayangan diperbesar 4 kali, maka letak benda harus 4 kali lebih dekat dengan lensa daripada letak bayangan. Oleh karena itu, letak benda adalah 18 cm dari depan lensa.

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10.

Sebuah benda diletakkan tepat ditengah antara titik fokus dan permukaan cermin cekung. Bayangan yang terbentuk adalah…1. Diperbesar 2 kali2. Tegak.3. Mempunyai jarak bayangan sama dengan jarak fokus4. Maya.Pernyataan yang benar adalah…

A.

1, 2, 3, dan 4
B.

1, 2, dan 3
C.

1 dan 3
D.

2 dan 4

Correct Answer
A. 1, 2, 3, dan 4

Explanation
The correct answer is 1, 2, 3, and 4. When an object is placed exactly in the middle between the focus and the surface of a concave mirror, the resulting image will be magnified 2 times, upright, have the same distance as the focal length, and will be virtual.

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