What I feel most about the thin lens focal length experiment

Experimental report of the determination of the focal length of the thin lens:1. There is no standard collimated light source.

2. The focal length of the lens is different for different frequencies of light, which is called chromatic aberration.

3. There is an error in the ruler of the light base itself.

4. When the beam deviates greatly from the main optical axis, there is also an error in focusing, which is called spherical aberration.

Meaning:

Early spectacle lenses were seen as thin lenses. The thickness of the lens is ignored, and the two principal points and two nodes of the lens are reduced to an optical center point. The light through this point does not twist and turn. The total mirrors of a thin lens are equal to the sum of the mirrors of the two refractive surfaces.

e.g. d1=+; d2=－。then d= . Convex and thin lenses incident with parallel rays can converge into one point, concave lenses disperse, and their reverse extensions converge a little (regardless of spherical aberration).

The distance from this point to the lens is the back focal length f of the thin lens'，f'=1/d。

The precautions for the measurement experiment of the focal length of a thin lens are as follows:

1) The choice of the focal length (f) size of the convex lens should be appropriate, not too small or too large, and it is advisable to take about 10cm: if the focal length (f) is too large, it is very likely to cause the candle to not be found to u>2f and f.

2) The length of the candle should not be too long or too short.

3) The laboratory should be as close to the dark room as possible, and there is no wind.

Precautions in the trial:

1) Attention should be paid when assembling convex lenses, candles and light screens.

The convex lens is fixed to facilitate the measurement of object distance and image distance, and the candle and light screen are not fixed, which is convenient for the candle and light screen to move.

Try to ensure that the "three hearts" - the candle flame center, the lens center, and the light screen center are adjusted to the same horizontal height, otherwise Shengchang will cause the image of the candle to not be in the center of the light screen or not on the light screen at all, so that the image can not be found.

If the laboratory is not a darkroom, care should be taken to place the candle away from the light and the side of the light screen facing away from the light to ensure that the image on the light screen is clear and bright.

2) When studying "the candle is upright and magnifying the virtual image within one focal length", there is no image on the light screen, and the light screen should be placed at one end of the light fixture seat or the light screen should be removed, and the image should be observed from the side of the light screen through a convex lens to the side of the candle.

Notes:1When using the instrument, it should be handled and handled gently, so as not to cause the instrument to be shocked and worn.

2.When adjusting the instrument, it should be adjusted in strict accordance with the rules of use, carefully and patiently observe the adjustment, and do not be impatient.

3.Do not touch the optical surface of the optical element with your hands at any time, and wipe it in accordance with the correct professional method.

1. There is no standard collimated light source.

2. The focal length of the lens is different for different frequencies of light, which is called chromatic aberration.

3. There is an error in the ruler of the light base itself.

4. When the beam deviates greatly from the main optical axis, there is also an error in focusing, which is called spherical aberration.

In the actual measurement of physical quantities, whether it is a directly measured quantity or an indirect measured quantity (the quantity calculated by the directly measured quantity through a formula), due to the limitation of factors such as measuring instruments, methods and external conditions, there is a difference between the measured value and the true value (or experimental average), which is called measurement error.

1. The coaxial adjustment of each component on the optical tool seat requires the following:

1) The optical axis of all components coincides;

2) The common optical axis is strictly parallel to the guide rail of the optical base;

Coarse adjustment: After clamping the lens, object, and screen with light and answering fixtures, first bring them closer together, adjust the height, left and right, so that the plane of the light source, object, lens, and screen is parallel to each other and perpendicular to the guide rail;

Fine adjustment: If the center of the object deviates from the optical axis of the lens, then in the process of moving the lens, the position of the image will change, that is, the center of the large image and the small image do not coincide, which is to judge whether the center of the object is left or right, up or down according to the cheap direction, and then adjust.

2. The focal length of the convex lens is measured by the object distance image distance method.

Use a white light lamp to illuminate the slit, a light transmission slit as an object, place the slit and the white screen on the light fixture base, a certain distance apart, and then put the convex lens to be measured in the middle of it, move the lens, so that the screen gets a clear narrow hail draft slit image, record the position of each light apparatus, calculate the object distance, image distance, and calculate the focal length f. Repeat three times to find the average.

3. Conjugate method to measure the focal length of the convex lens.

Fix the slit light source and the screen at a position where the distance is greater than 4F, measure the distance between them, place the convex lens to be measured between the light source and the white screen, move the convex lens, get a clear slit image on the screen, record the position of the lens, move the lens to another position, make the screen get a clear slit image again, record the position of the lens, calculate the distance d from the two positions and find F, repeat three times, and find the average value.

1. Physical imaging method.

Experimental principle: convex lens.

The physical object is used as the light source, and the light emitted by it is converging through the lens.

After that, under certain conditions, the real image can be observed, and the object distance and image distance are determined, and then the Gaussian formula of the thin lens in the air is used to start the stove.

The focal length is calculated.

2. Self-quasi-method.

Experimental principle: When the luminous point is in the focal plane of the convex lens, the light emitted by it will become a beam of parallel light after passing through the lens. If the parallel light is reflected back by a plane mirror perpendicular to the main optical axis, the reflected light will still converge on the focal plane of the lens after passing through the lens again, and its convergence point will be in the symmetrical position of the luminous point relative to the optical axis.

1. There is no standard collimated light source.

2. The focal length of the lens is different for different frequencies of light, which is called chromatic aberration.

3. There is an error in the ruler of the light base itself.

4. When the beam deviates greatly from the main optical axis, there is also an error in focusing, which is called spherical aberration.

In the actual measurement of physical quantities, whether it is a directly measured quantity or an indirect measured quantity (the quantity calculated by the directly measured quantity through a formula), due to the limitation of factors such as measuring instruments, methods and external conditions, there is a difference between the measured value and the true value (or experimental average), which is called measurement error.