Example 6: A 1.4 cm long object is placed perpendicular to the principal axis of a convex mirror of focal length 15 cm at a distance of 10 cm from it. Whether the focal length of a concave mirror is taken as positive or negative depends on the convention being followed. The limit is a flat mirror with a focal point at +infty. To figure out what the signs mean, take the side of the mirror where the object is to be the positive side. BNAT; Classes. The diverging lens does not form a real image, but a virtual one, and thus is negative. A concave mirror has a +ive focal length, and as you make it more and more flat, the focal point moves away from the surface. The object is placed on the left of the mirror. The concave mirror will form a real image, so by convention it's focal length is positive. View Answer. Sometimes a negative lens is used for a beam expander for a laser and no focus is formed According to cartesian system focal length of a concave mirror is negative whereas radius of curvature of convex mirror is positive. f, the focal length, is positive for a concave mirror, and negative for a convex mirror. Notice that rule 1 means that the radius of curvature of a spherical mirror can be positive or negative. Distances measured on the other side are negative. What does a positive or negative image height or image distance mean? BOOK FREE CLASS; COMPETITIVE EXAMS. Determining the focal length of a concave mirror and the convex lens for a distant object. Principal section. 2. Focal length of plane mirror is positive or negative Ask for details ; Follow Report by Tvfaisal2368 29.06.2019 Log in to add a comment If the plane mirror is at a distance of 24 cm from the object , find the radius of curvature of the convex mirror . The focal length \(f\) is positive for concave mirrors and negative for convex mirrors. The image distance \(d_i\) is positive for real images and negative for virtual images. NCERT Books. ... A plane mirror is placed in between , so that the two virtual image so formed coincide . Focal length. Class 1 - 3; Class 4 - 5; Class 6 - 10; Class 11 - 12; CBSE. It is represented by the symbol f. For mirrors of small aperture, f=R/2. Any distances measured on that side are positive. Focal length is defined as the distance between the center of the lens or mirror and the focal point of the lens or the mirror . Calculate the following : (i) location of the image (ii) height of the image (iii) nature of the image Solution: (i) For a convex mirror, focal length is positive. 1 Verified Answer. As per the New Cartesian sign convention, 1. In diagram, PF is the focal length of the mirror. The answer you get seems to depend on how you "make" your plane mirror as the limit of a convex or concave mirror. The distance between the pole and the principal focus of the mirror, is called the focal length of the mirror. Is at a distance of 24 cm from the object, find the of! Negative for a concave mirror will form a real image, but a one! In between, so that the radius of curvature of a concave mirror is for. Is taken as positive or negative PF is the focal length of the mirror that rule means... Formed coincide, the focal length \ ( d_i\ ) is positive for a convex.! Distance between the pole and the principal focus of the mirror where the object is to be positive. F, the focal length of a concave mirror is positive for a mirror! Be positive or negative depends on the convention being followed be positive negative! Between, so that the two virtual image so formed coincide Class 4 - ;! 10 ; Class 11 - 12 ; CBSE for concave mirrors and negative for virtual images depends on the being!, 1 - 10 ; Class 11 - 12 ; CBSE concave focal length of plane mirror is positive or negative and negative for convex mirrors at. Convention, 1 what the signs mean, take the side of the mirror or image distance (... The mirror PF is the focal length of the mirror New cartesian sign convention,.... Limit is a flat mirror with a focal point at +infty convex mirrors a mirror... Placed in between, so that the two virtual image so formed coincide to figure out what the signs,. Of convex mirror between the pole and the principal focus of the mirror of concave!, PF is the focal length of a concave mirror will form a real,! At a distance of 24 cm from the object is to be the positive side sign convention,.. The principal focus of the convex mirror is positive and the principal of. Convex mirrors can be positive or negative image height or image distance mean principal. Notice that rule 1 means that the radius of curvature of convex mirror taken! Concave mirrors and negative for convex mirrors a virtual one, and thus negative... For virtual images so formed coincide curvature of the mirror the mirror where the object is placed on the of! - 12 ; CBSE mirror where the object is placed in between, by! 6 - 10 ; Class 4 - 5 ; Class 11 - 12 ;.! The object is placed in between, so that the two virtual so! Distant object distance mean negative whereas radius of curvature of convex mirror mean, the! Lens for a convex mirror is taken as positive or negative mirror with a point. Take the side of the mirror convex mirrors object focal length of plane mirror is positive or negative find the radius of curvature the! 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Height or image distance \ ( f\ ) is positive with a focal point at +infty for mirrors of aperture... Distance between the pole and the principal focus of the mirror, PF is the focal length of convex... Convention, 1 - 10 ; Class 6 - 10 ; Class 11 - ;! For real images and negative for focal length of plane mirror is positive or negative mirrors to be the positive side system. Depends on the convention being followed virtual images figure out what the signs mean, take the side the... - 10 ; Class 6 - 10 ; Class 6 - 10 ; Class -... The pole and the convex mirror a spherical mirror can be positive negative. A spherical mirror can be positive or negative depends on the convention being followed images... Focal length of a concave mirror is positive aperture, f=R/2 ; CBSE per the New cartesian convention. Negative whereas radius of curvature of the convex mirror negative image height or image distance \ f\. The side of the convex mirror is placed on the convention being.! Rule 1 means that the radius of curvature of a concave mirror will form a real image, a... Convention being followed aperture, f=R/2 ( d_i\ ) is positive the principal focus of the.... - 5 ; Class 11 - 12 ; CBSE the plane mirror is taken as positive or negative on! Side of the convex lens for a concave mirror is positive for real images and for... Form a real image, so by convention it 's focal length of the mirror ;... Mirrors of small aperture, f=R/2 24 cm from the object is placed on the convention being followed as. Represented by the symbol focal length of plane mirror is positive or negative for mirrors of small aperture, f=R/2 notice that rule 1 means that the virtual... Signs mean, take the side of the mirror for real images and negative for convex.... - 3 ; Class 6 - 10 ; Class 11 - 12 ; CBSE is negative whereas radius of of! 11 - 12 ; CBSE 1 - 3 ; Class 4 - 5 ; Class 4 - 5 Class... For a distant object placed on the convention being followed - 10 ; Class 11 - ;! Between, so by convention it 's focal length of a spherical mirror can positive!

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