Learn more about Reflection of Light here. A concave lens of focal length 15 cm forms an image 10 cm from the lens. Physics Grade XI Reference Note: Mirror formula for concave mirror when real image is formed and for convex mirror. The two formulas given above are together referred to as the thin lens formula. u   =   object distance Please note that the magnification formula is applicable both in convex lenses and concave lenses. Exercise 2. (a)For an object with u= 12cmif the focal length is 4cm What will be the distance of the object, when a concave mirror produces an image of magnification m? On the other hand, the magnification m is negative when the image formed is real and inverted. Where, \(v\) is the object height \(u\) is the image height. The sign conventions for the given quantities in the lens equation and magnification equations are as follows: f is + if the lens is a double convex lens (converging lens) f is - if the lens is a double concave lens (diverging lens) d i is + if the image is a real image and located on the opposite side of the lens. The magnification is negative for real image and positive for virtual image. And the magnification m is positive when the image formed is virtual and erect. Lens formula is applicable for convex as well as concave lenses. Using lens formula the equation for magnification can also be obtained as m = h2/h1 = v//u = (f-v)/f = f/ (f+u) This equation is valid for both convex and concave lenses and for real and virtual images. Section 3: Concave Lenses 14 Here are some exercises with concave lenses. We also have another formula for magnification in lenses Magnification = v/u where v is image distance u is object distance Note: - If magnification (m) is positive, It means image formed is virtual and erect If magnification (m) is negative, It means image formed is real and inverted Questions Example 10.3 - A concave lens has focal length of 15 cm. In the case of a concave lens, it is always positive. Be careful with the sign of the focal length in the lens formula! The focal length of the mirror is f. a. Example Problem #1 A 4.00-cm tall light bulb is placed a distance of 45.7 cm from a concave mirror having a focal length of 15.2 cm. It is an equation that relates the focal length, image distance, and object distance for a spherical mirror. Table shows the sign convention for the values of object distance, image … Example 2: The distance of an object of height 6 cm from a concave lens is 20 cm. Determine the image distance and the image size. Object distance (o) = + 20 cm Now by putting the values of (f) and (o) in 1/v+ 1/o = 1/f, we will get, 1/v = 1/f - 1/o On the other hand, the magnification m is negative when the image formed is real and inverted. If the magnification is positive, then the image is upright compared to the object (virtual image). Please note that the magnification formula is applicable both in convex lenses and concave lenses. Online physics calculator that calculates the concave mirror equation from the given values of object distance (do), the image distance (di), and the focal length (f). And the magnification m is positive when the image formed is virtual and erect. Solution: As the lens here is concave, the focal length (f) = -10 cm. If its focal length is 10 cm, calculate the size and position of the image formed. As a demonstration of the effectiveness of the mirror equation and magnification equation, consider the following example problem and its solution. (click on the green letters for the solutions). Calculate the position of the images formed by the fol-lowing concave lenses. Define lens formula. Magnification of Convex Lens: It is a ratio between the image height and object height. Magnification of Convex Lens: It is a ratio between the image height and object height. An expression showing the relation between object distance, image distance and focal length of a mirror is called mirror formula. An object 5 cm high is held 25 cm away from a converging lens of focal length 20 cm. Assumptions and Sign conventions Q. You can try the following sample problem using this. Therefore, the relationship between the object distance, the image distance and the focal length of a lens is given by the \( \text{Lens Formula: }\frac{1}{u}+\frac{1}{v}=\frac{1}{f} \) The lens formula may be applied to convex lenses as well as concave lenses provided the ‘real is positive’ sign convention is followed. Is lens formula applicable only for convex lens? 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