Tổng hợp kiến thức gương cầu lõm vật lý 7

In the 7th grade physics program, we will learn about the convex mirror and concave mirror. Each type of mirror possesses different characteristics and uses and applications. The following article, Mầm non Cát Linh will summarize the most necessary knowledge about the concave mirror so that you can learn, learn and apply well in your daily life.

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What is concave mirror?

The concave mirror, also known as another name is a divergence mirror. The surface of the mirror is composed of a slightly concave spherical part. The reflex surface of the mirror will be the concave part of the spherical, towards the light source.

Photo of an object created by concave mirror

Different from the convex mirror, the image properties of the object created by the concave mirror will also have a difference, depending on the location and relative distance of the real object compared to the center and focus of the mirror.

Conduct the following experiment to better observe the image of an object created by the concave mirror:

• First, we need to prepare a concave mirror and a candle

• After that, put the tree close to the mirror surface. At that time, looking at the mirror, we will see a virtual image (not inspired on the screen), which is larger than the object.

• Move the candle away from the mirror until we can’t see that image anymore.

Comment:

• The image of any object created by a concave mirror may be virtual or real image

• When placing objects near the mirror, the image we obtained is a virtual image, larger than the object and not inspired on the screen

• When proceeding to translate the object away from the concave mirror and use a screen to set in front of the mirror. We see that when moving candles to an appropriate position, the image will be obtained on the screen. At this time, the image is created by a concave mirror is a real image, opposite to the object.

Light reflection on the concave mirror

Projecting a bunch of light rays parallel to the face of the concave mirror, we will obtain a beam of reflection of the reflection in the mirror at a point.

In an appropriate position, shining a light source into the mirror surface of the concave, we obtained a beam of light reflection.

Conclude:

• The concave mirror has the effect of converting a beam to a divergence into a beam of parallel reflection rays.

• The concave mirror has the effect of converting a beam in parallel to a beam of reflections that converge at one point.

• We can apply the concave mirror to collect to focus the sunlight: Use flat mirrors to focus light into a concave mirror. This concave mirror will focus and reflect light, heat the furnace and then, people will obtain solar energy.

How to draw photos created by concave mirrors

We can see each area on the concave mirror as a small flat mirror surface. Applying the law of light reflection, we will infer how to draw photos created by the concave mirror as follows:

• First, draw the image of the bright spot S created by a concave mirror: from the given point S, draw two rays (SK, SI) any towards the concave mirror (instant strokes).

• Apply the law of light reflection to draw the corresponding reflection rays (instant strokes).

• After the reflection rays have been drawn, proceed to prolong the reflection (drawing broken strokes).

• The intersection of the extended part of the two reflection rays is the virtual image s’.

Concave mirror formula

Here is the formula for concave mirrors that you need to know to apply to solving exercises and calculating the actual parameters.

The formula for focal length f with distance d is calculated from mirrors to objects and distance f from mirror to photo:

1d+1f = 1F

There are 2 cases:

• Case 1: f <d, when d <0, f <0 and f <0 will produce real photos.

• Case 2: f> d, when d <0, f <0 and f <0 will produce virtual images.

In the formula of the concave mirror, the distance D from object to the mirror is always the positive number. When parameters f <0: If f 0 will obtain real photos.

From this formula, we can draw the way of drawing the virtual image of an exact object through the concave mirror, which is for parameters f <0, we will draw virtual images.

Besides, there is a formula that you should also note:

F = r2

In which: R is the curved radius of the mirror, f is the focal length of the mirror

Application of concave mirror

The concave mirror has many applications in real life. You can see the concave mirror used in many fields such as health, traffic, cosmic astronomy, …

In the field of life

Used as a mirror for shaving and makeup

When searching near the concave mirror, the image will be clearly reflected on the mirror. Therefore, for those who need shaving, makeup, skin care, you can easily see clearly the expanded image of the skin. This allows you to observe and scrape off the same length as well as makeup all the skin on your face, helping you have a desired appearance.

Used as a car headlight

People apply the properties of the strong light of the concave mirror to design the headlights of the motor vehicle. They have the ability to focus on the light from the light bulb to create a strong beam on the road, so that the driver can observe the running road clearly, avoiding unnecessary accidents.

See also: Summary: What is a flat mirror? The properties of the image created by a flat mirror? (+ Physical BT Prize 7)

Microscope

You can find a concave mirror near the base of the microscopes. In particular, the concave mirror in this case can rotate in all directions, not fixed. People use the concave mirror in the microscope with the effect of collecting light from the lights to shine on the sample to analyze. Thereby, we can see the sample clearly and detailed through the magnified lens.

However, it should be noted that the mirror is concave towards sunlight because the mirror will focus on the sunlight. Meanwhile, the intensity of this light is too strong can affect the vision of the person looking through the lens.

In the field of astronomy

Similar to how to operate in the microscope, the concave mirror is also designed simultaneously with astronomy. But otherwise, instead of shining the light on the sample to be analyzed, the concave mirror of astronomical glass will be the task of collecting light and lighting from the stars in the universe on a flat mirror. As a result, users of astronomical glass will be able to see the stars through the lens that the naked eye cannot see.

Solving physical exercises 7 lessons 8 mirrors concave

Here are some multiple choice questions to help you reinforce your knowledge and remember the lesson more effectively.

Question 1: Which of the following is a virtual image created by a concave mirror?

A. Big as objects.

B. larger than objects.

C. much smaller than objects.

D. smaller than the image created by a convex mirror.

Answer: B

Question 2: Projecting a beam of light parallel to the concave mirror surface, which of the following beams of reflections are we obtained?

A. Parallel.

B. Convergence.

C. divergence.

D. Do not pass in a straight line.

Answer: B

Question 3: Why do people not use the concave mirror on the car to observe the virtual photos of the objects behind the car more clearly?

A. Because the image is not clear.

B. Because the object must be very close to the new mirror for the virtual image.

C. Because virtual images are smaller than things.

D. Because the virtual image is located away from the mirror in the back of the eyes.

Answer: B

Question 4: Of the three types of mirrors (flat mirrors, convex mirrors, concave mirrors), which mirrors will give the virtual image of the same object larger? Ranked in order from left to right.

A. Flat mirrors, concave mirrors, convex mirrors.

B. Concave mirrors, convex mirrors, flat mirrors.

C. Concave mirrors, flat mirrors, convex mirrors.

D. Convex mirrors, flat mirrors, concave mirrors.

Answer: D

Question 5: Why can the reflection mirror, the flashlight can show the light away?

A. Because of the mirror, the light will return

B. Because the mirror for more virtual images

C. Because it is a concave mirror for parallel beams

D. Because thanks to the mirror we see things far away

Answer: C

Question 6: What is the reflection of the concave mirror?

A. The inside of the bridge

B. The outer surface of the bridge

C. The plane is like a flat mirror

D. A, B, C are right

Answer: A

Question 7: What is the mirror that occurs the phenomenon of light reflection when there is light transmitted?

A. Flat mirrors

B. Convex mirrors

C. The concave mirror

D. All three types of mirrors

Answer: D

Question 8: Choose the best answer in the following sentences:

A. The concave mirror always creates virtual images

B. The concave mirror can give both real photos and virtual images. The virtual image of the object through the concave mirror is larger than the object

C. Because the concave mirrors for the image are larger than the object but still smaller than the convex mirror

D. Because the width of the visible area of ​​the convex mirror is larger than the concave mirror of the same size and the convex mirror for the virtual image is smaller than the object

Answer: B

Question 9: Why do people install convex mirrors but not concave mirrors in the corners of narrow crabs, although the concave mirror can still give virtual images larger than objects such as convex mirrors.

A. Because the convex mirrors give more clear images

B. Because the convex mirrors always give virtual photos

C. Because the concave mirrors for the image are larger than the object but still smaller than the convex mirror

D. Because the width of the visible area of ​​the convex mirror is larger than the concave mirror of the same size and the convex mirror for the virtual image is smaller than the object.

Answer: D

Question 10: Choose the best answer in the following sentences

A. The concave mirror for the image is smaller than the object, but the further the object is, the more the size of the image increases

B. The concave mirror for the image is larger than the object, but the smaller the object is to the size of the image

C. If the object is moving away from the concave mirror, a larger distance from the mirror of the mirror, the concave mirror will give a very smaller image than the object and in the opposite direction.

D. Photos through the concave mirror are always virtual photos

Answer: C

Conclusion

Above is a summary of the knowledge to know about the concave mirror that readers can refer to. Hopefully, through the article, you have accumulated a lot of useful information, understand the properties and applications of the concave mirror to apply well in both learning and real life. You can refer to many other articles at the website https://mncatlinhdd.edu.vn/ba-me-can-biet/giao-duc/kien-thuc-co-ban/

Nguồn: https://mncatlinhdd.edu.vn/ Tác giả: Nguyễn Lân dũng