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What is a converging lens?

In the optical definition, a lens is an optical device used to focus or diverge different beams of light. In a broader context, an optical lens is a lens that works with light and with traditional techniques.

What image does a converging lens produce? The converging lens is a transparent colored lens with a thinner edge than the middle. They are usually bounded by two spheres or one plane and one sphere.

This is a lens where the light beam after passing through the glass will converge to a point.

Features of converging lenses

Features of converging lenses include:

Rays of light through the lens

• The ray of light that reaches the lens is called the incident ray, the ray that comes out is the ray that is refracted from the lens.

• When the ray reaches the optical center, the reflected ray continues to propagate in the opposite direction to the incident ray.

• An incident ray parallel to the principal axis will emerge through the focal point.

• An incident ray passing through the focal point of the object emerges parallel to the principal axis.

Shape of converging lens

A converging lens is limited by two spheres (the sphere can be a plane). The outer border will be thinner in the middle.

Materials used to make converging lenses

There are many materials that can be used to make converging lenses. Usually it is made of a transparent material, typically plastic or glass.

1. Plastic lens

This is the best material for making converging lenses because it is easy to use for all subjects. Lenses made of plastic are also known as organic glass. For this type of glass is often used in making glasses for children or when playing sports because of its comfort as well as lightness as well as extremely high resistance to breakage.

2. Glass lens

These lenses are made of good quality natural mineral glass, which is professionally graded and is the standard for these products. With this type of lenses, consumers will be less expensive than using plastic lenses, especially they have extremely high scratch resistance and are suitable for cases of severe myopia.

How to recognize a converging lens?

To be able to recognize the converging lens, you can refer to the following 3 ways.

• Use your hand to define them by the thickness of the center and the thickness of the edges. If the edge of the lens is thinner than the middle, it is a converging lens.

• Bring the lens closer to the text on the book. If the lens can make the text seen through the lens larger than directly on the book, it is a converging lens.

• Use a light-gathering lens. Use a lens to catch the light of a distant lamp on the screen. If the light beam is focused on the screen, it is a converging lens.

Principal axis, optical center, focal point, focal length of converging lens

Here are the concepts surrounding converging lenses to keep in mind

Major axis of converging lens

The main axis of the converging lens is the emergent ray, which can pass straight through the object and is not changed direction when it passes through the lens.

Optical center of converging lens

Focal point of converging lens

The focal point of converging lenses is denoted F. They have the emergent beam converging at a point and the incident beam parallel to the principal axis of the lens.

• When the incident ray passes through the optical center O, the reflected ray will travel in a straight line.

• The incident ray is parallel to the principal axis and then the reflected ray passes through the focal point F’.

• The ray incident through the focal point F is parallel to the principal axis.

Focal length of converging lens

where the focal length of the converging lens is the distance from the focal point F of the lens to the optical center O of the lens, denoted f and measured in cm.

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How to draw a converging lens

• Draw the horizontal main axis denoted by (△).

• Construct the lens perpendicular to the principal axis. The symbol for the point passing through the optical center is (O).

• The incident beam is parallel to the principal axis of the converging lens. The principal focus is the emergent beam converging at a point on the principal axis.

• The principal focus is two points located on the principal axis a distance from the lens and symmetrical about one side of the focal point F, we have a focal point F’ on the other side of the lens.

You can refer to the image below:

Image of an object through a converging lens

Distance from object to lens (d)	Features of the photo
	Image position (d’) (CO = C’O = 2OF)	Image properties
The object is very far from the lens	d’ = OF’	real image
d > 2f	photo at F’C’	The real image is inverted and smaller than the object
d = 2f	image at C’ (with OC’ = 2OF)	Real photos of people with objects and objects
f = d	from C’ to	The real image is inverted and larger than the object
d = f	IN	no photo
d	in front of the camera	virtual image, in the same direction as the object and larger than the object

To render the image A’B’ of segment AB through the lens (AB is perpendicular to the lens and point A lies on the principal axis), simply construct the image B’ of B using two of the three special rays, thus lowering B ‘ perpendicular to the main axis △ we get the image A’ of A.

Converging lens formula

The formula for relation between object position, image position and lens focal length

Dividers:

• Converging lens: f > 0

• Diverging lens: f

• Real photo :d’ > 0

• Image is virtual :d’

• Object is real: d > 0

The formula for calculating the magnification of a lens is:

Dividers:

The formula for calculating the condenser of a lens is:

In there:

• n: refractive index of the lens material

• D: converging lens

• f: focal length of the lens (m)

• R1; R2: radius of curved surfaces (R = for plane case) (m)

Applications of converging lenses in daily life

As for converging lenses, they are used for many different purposes in life. Some applications include:

• Convert parallel beams into focused beams.

• Used as objective and eyepiece in microscope or telescope.

• Used as a camera lens.

• Use as a magnifying glass.

• Used as glasses to correct farsightedness and farsightedness.

• Sometimes converging lenses are also used in many emergencies such as creating a fire.

See also: What is a diverging lens? What is the image of an object through a diverging lens? (Physics 9)

Some exercises for converging lenses in class 9

Question 1: A converging lens turns a parallel incident beam into what beam?

A. Reflected rays.

B. Converging beam.

C. Divergent beam.

D. Another parallel flare.

Question 2: When an incident ray passes through the optical center of a converging lens, a reflected ray is emitted?

A. Passes through the focal point and passes through the optical center

B. Parallel to the principal axis and passing through the focal point

C. The direction of propagation is straight in the direction of the incident ray.

D. There is a line extending through the focus

Question 3: What materials are often used to make lenses?

A. Clear glass

B. Transparent plastic

C. Aluminum

D. Water

Question 4: Which of the following statements is true about converging lenses?

A. The principal axis of the lens is any line segment of infinite length.

B. The optical center of the lens is equidistant from the two focal points.

C. The focal point of the lens depends on the area of ​​the lens.

D. The distance between two focal points is called the focal length of the lens.

Question 5: Bright object AB has the shape of an arrow 6 cm high placed perpendicular to the principal axis of the converging lens, 15 cm from the lens. The lens has a focal length of 10 cm.

a/ Constructing an image of an object through a lens

b) Determine the size and position of the image

Question 6: Bright object AB has an arrow shape 6 cm high and is placed perpendicular to the principal axis of the converging lens, 10 cm from the lens. The lens has a focal length of 15 cm.

a/ Constructing an image of an object through a lens

b) Determine the size and position of the image

Question 7: A bright object AB in the shape of an arrow placed perpendicular to the principal axis of a converging lens produces a real image 12 cm high, 30 cm from the lens. The lens has a focal length of 10 cm.

Determine the size and position of the object

Question 8: Object AB is placed in front of a converging lens for image . Prove the lens formulas and .

Question 9: Let Δ be the principal axis of a lens, S is the bright spot, and S’ is the image of S formed by the lens.

a) Is S’ a real image or a virtual image?

b) What is the given lens?

c) Draw a picture, show how to build.

Question 10: Given a bright object AB 1 cm high, placed in front of a converging lens and 15 cm from the lens, the real image is 0.6 cm high.

One. Draw a picture

b. Calculate the focal length of the lens and the distance from the image to the lens

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