For determining the focal length of a concave mirror
How can we find the approximate focal length of a concave mirror quickly?
Hold the concave mirror facing some distant object like a tree. Hold a cardboard screen in front of the mirror.
Adjust the position of the screen
so that a sharp image of distant object is formed on the screen. The distance of screen from the mirror gives us the approximate focal length of the concave mirrror.
How could you find focal length of a convex lens rapidly but approximately?
Put a paper and put the lens in front of it and capture the image of a distant object by moving the lens to and fro. When a sharp and inverted image is formed, measure the distance between the lens and the paper. That is a rapid and approximate method of measuring the focal length of the lens.
How do you find the approximate focal length of a convex lens?
By
moving the convex lens to and fro along the scale, focus a distant object on wall
. The image which forms on the wall is very near to the focus of the lens and the distance of the lens from the image is read directly by the metre scale. This gives the approximate focal length of the lens.
What is the focal length of curvature?
It is located at the midpoint of pole and centre of curvature.
The distance between the pole and the focus of the mirror
is called the focal length of the mirror. Note: Focal length of the mirror is a measure of power of the mirror.
How do you find the focal length of a concave mirror in Class 10?
As the distance between the pole 0 of the concave mirror and the focus F is the focal length of the concave mirror. Thus, the focal length of a concave mirror can be estimated by
obtaining a real image of a distant object at its focus
.
Which type of spherical mirror has positive focal length?
Out of the two-spherical mirror,
convex mirror
has positive focal length. Concave mirror forms a real and inverted image of the object at ‘F’ point which can be taken on the screen.
What do you mean by the statement a convex lens has a real focus?
A convex lens is said to have a real focus and a concave lens a virtual focus. … In a convex lens,
the parallel rays of light passing through the lens actually meet at the focus in front of the lens
. This is why it is called real focus.
What do you mean by virtual magnified image?
(a) A virtual magnified image is
the one which cannot be taken on a screen and whose size is larger than that of the object
.
What are the uses of convex lens?
- A convex lens is employed in microscopes and magnifying glasses to converge all incoming light rays to a particular point. …
- The convex lens is used in cameras. …
- A convex lens is used for the correction of hyperopia. …
- The converging lens is used in the projector as well.
How do you find approximate focal length?
By
moving the convex lens to and fro along the scale, focus a distant object on the wall
. The image which forms on the wall is very near to the focus of the lens and the distance of the lens from the image is read directly by the metre scale. This gives the approximate focal length of the lens.
How is focal length calculated?
Focal length =
(Object distance / ((1 / Magnification) + 1)) * 1000
, where: Object distance is given in mm; and. Magnification does not have a unit.
How do you find the approximate focal length?
Measure the approximate focal length of the lens by
focusing a distant object onto a screen and measuring the distance from the lens to the screen using the metre stick
.
How do you find the focal length when center of curvature is given?
The relation between focal length (f) and radius of curvature (R) of a spherical mirror is that the focal length is equal to half of the radius of curvature i.e.
f=R2
.
How do you find the focal length from the radius of curvature?
Focal Length of a Curved Mirror
A mirror with a curvature radius R of the surface has a
focal length f = R / 2
, if the beam axis is normal to the mirror surface.
What is focal length class 10?
The distance between the convex lens or a concave mirror and the focal point of a lens or mirror is called the focal length. It is
the point where parallel rays of light meet or converge
.
How do you find the focal length of a convex mirror?
You can measure the radius of curvature (R) of the mirror by measuring the distance between convex mirror and the screen placed behind the mirror. You can calculate the focal length of the mirror using the equation
f = R/2
.
What is the focal length of a plane mirror?
However the focal length of a plane mirror is
infinity
; its optical power is zero.
Which lens has positive focal length?
The distance from the lens to the focal point is called the focal length. For
converging lenses
, the focal length is always positive, while diverging lenses always have negative focal lengths.
Is focal length positive?
(a) A
convex mirror
has a positive focal length because the focus of a convex mirror is on the right side and behind the mirror. … The focal length of a concave mirror is negative, and that of a convex mirror is positive.
Does a convex lens have a real or virtual focus?
A
convex lens is said to have a real focus
and a concave lens a Virtual Focus. Why? Convex lenses bend parallel light rays to form a point at a given distance, called the focal length. Concave Lenses bend parallel light rays in the opposite Direction, so they never form a point.
How is focal length of a lens affected if a part of the lens is covered?
Therefore, the half part of a convex lens is covered; the focal length does not change, but the
intensity of the image decreases
.
On what factors focal length of a lens depends?
So, focal length depends on
the radius of curvature
, the refractive index of lens material, and the medium’s refractive index in which the lens is placed.
When we get virtual and magnified image with convex lens?
The convex lens produces a virtual image when
the object is placed between the pole of the lens and first principle focus
. The image formed by a concave lens is never magnified. The convex lens produces magnified images when the object is placed between the first principal focus and pole of the lens.
Which type of mirror magnifies the image?
The upright images produced by
concave mirrors
(when object is in front of F) are magnified images. And the upright images produced by plane mirrors have the same size as the object.
What kind of lens can form an erect image larger than the object?
Question 7: State two differences between a convex and a concave lens. Answer:
A convex lens
can make enlarged image, while a concave lens would always make smaller image.
Which mirror is used in vehicles?
Convex mirror
: different uses
One of the most common uses for the convex mirror is the passenger-side mirror on your car. These convex mirrors are used for cars because they give an upright image and provide a wider field of view as they are curved outwards.
How do you find the focal length of an experiment?
There is a trick to this:
place a piece of white paper next to the object so that you can see an image on the paper
. The distance from the object to the lens is the focal length. Repeat this measurement five times.
How do you find the combined focal length?
If the lenses of focal lengths f
1
and f
2
are “thin”, the combined focal length f of the lenses is given by 1
f=1f1+1f2 1 f
= 1 f 1 + 1 f 2 while if the lenses are separated by some distance d then the combined focal length is given by 1f=1f1+1f2−df1f2 1 f = 1 f 1 + 1 f 2 − d f 1 f 2 .
Which lens is used in telescope?
This type of telescope is called a refracting telescope. Most refracting telescopes use two main lenses. The largest lens is
called the objective lens
, and the smaller lens used for viewing is called the eyepiece lens.
Which lens is used in flashlight?
Concave lenses
are also used in flashlights to magnify the light produced by the source. The light rays fall on the hollowed side of the lens, and the light rays diverge on the other side.
How do you find the focal length of a class 10?
Place the screen in front of the reflecting surface of the mirror. Move the screen back and forth until a clear, sharp image of the distant object is obtained on the screen.
Measure the distance between the
concave mirror and the screen with a metre scale. This distance is the focal length of the given concave mirror.
How do you find the focal length of a convex lens without calculating?
Explanation:
Place the convex lens in such a position that sunlight is perpendicular to the lens
. In such a position sunlight would be parallel to the optical axis of the lens. Place a piece of paper behind and parallel to the lens and adjust its distance from the lens so as to obtain a point image of sunlight.
Is the Centre of curvature twice the focal length?
Yes, the radius of curvature is
twice the focal length from
the pole (A in upper diagram, P in lower diagram) : R=2f. You can obtain an approximate value of f by finding the point at which a distant object is focussed, as suggested by the 2nd diagram.
Is focal length half of the center of curvature?
| f ≈ r | 2 |
|---|
Is the center of curvature 2f?
| SIGN + – | m – magnification Upright image Inverted image |
|---|
