"Laws of Imaging by Convex Lenses" Lenses and Their Applications PPT Courseware 5

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"Laws of Imaging by Convex Lenses" Lenses and Their Applications PPT Courseware 5

How to ensure that the image of the candle is always on the light screen?

Adjust the centers of the candle, lens, and light screen so that their three centers are at the same height, so that the image of the candle flame is in the center of the light screen.

How to measure the focal length of a convex lens?

According to the characteristics of the convex lens, allow parallel light (such as sunlight) to be incident on the convex lens along the main axis. Place a light screen parallel to the lens on the other side. Adjust the position of the light screen to make the light spot on the light screen the smallest and brightest. At this time, the lens The distance from the light screen is the focal length of the convex lens. This is a simple method to roughly measure the focal length of a convex lens.

Experimental expansion

1. In the experiment, can you find where the dividing point between the real image and the virtual image is?

The focus is the dividing point between real and virtual images

2. In the experiment, can you find where the dividing point between the enlarged image and the reduced image is?

The double focal length is the dividing point between the reduced image and the enlarged image.

3. Under what circumstances are images and objects on both sides of a convex lens? Under what circumstances are the image and the object on the same side of a convex lens?

When forming a real image, the object is on the opposite side

When creating a virtual image, the object is on the same side as the image

4. When a convex lens forms a real image, how does the image distance change as the object distance decreases?

The object distance decreases and the image distance increases

That is, objects and images move in the same direction

Like moving with an object

Practice in class

Example: As shown in the figure, keep the position of the convex lens unchanged, place the candle flame at points a, b, c, d, and e, and adjust the position of the light screen respectively. but:

1. Place the candle flame at _______ point, and the image that appears on the screen will be the largest; put the candle flame at _______ point, and the image that will appear on the screen will be the smallest.

2. Place the candle flame at the _______ point. When a clear image appears on the screen, the screen is farthest from the convex lens.

3. Place the candle flame at _______ point, and there will be no image on the screen.

Example: In an experiment using candles to study the imaging of convex lenses, the focal length of the convex lens is 10cm. The lit candle is placed 15cm away from the convex lens. A clear image of the candle is observed on the light screen on the other side of the convex lens. This image must be ( )

A Real image inverted and enlarged

B inverted and reduced real image

C upright enlarged real image

D upright magnified virtual image

Example: When the distance between an object and the convex lens is 30cm, a magnified real image is obtained on the light screen. If the object is moved to a distance of 65cm from the convex lens along the main optical axis of the convex lens, the imaging situation is ( )

Analysis: The properties of the image produced by the convex lens are related to the object distance. From the real image of the first inverted magnification, we can know: f2f. So it becomes an inverted and reduced real image.

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Update Time: 2024-10-03

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