All Rights Reserved. 3) For most users a 3X or a 5X mirror works very well. The center of curvature of a mirror is the point in the center of the sphere from which the mirror is cut. Only convex mirrors can form virtual and diminished image. When objects are beyond the focal point of the mirror, the images seen are real images, but they are inverted. A magnifying mirror, otherwise known as a concave mirror, is a reflecting surface that constitutes a segment of the inner surface of a sphere. He contributes to LIVESTRONG.COM, eHow, and Answerbag.com. How do you find the image distance and magnification? The bottom of the image is a point on the axis directly below the top of the image. Skipping the details for the moment – up to a point, the further away the user gets from the mirror the larger the image. Consider the following example: an object 12 inches tall is placed a distance of 4 inches from a concave mirror that has a focal length of 6 inches. When objects are positioned between the focal point of a concave mirror and the mirror's … How do magnifying mirrors work – the easy stuff? The image distance must first be determined with this equation before the image magnification can be determined. He is an avid amateur astronomer, accomplished chess player, and a health and fitness enthusiast. The magnification is also equal to the negative of the ratio of the distance of the image from the mirror … First let’s define some of the variables A magnifying mirror, otherwise known as a concave mirror, is a reflecting surface that constitutes a segment of the inner surface of a sphere. a. In a concave mirror, the magnification is the ratio of the height of the image to the height of the object. Basically they track the path of two light rays as they pass through specific points and are reflected from the face of the mirror. How do magnifying mirrors work – the technical stuff. Q. The curvature of the glass – for any given mirror this is a fixed number and doesn’t change. The focal length of the mirror … The Physics Classroom: Concave Mirrors, The Mirror Equation. 2) Magnifying mirrors are rated for their power of magnification based on how much bigger they make an object look. The distance of the user from the mirror, which, of course, is variable. For make‐up and shaving mirrors the most common ratings are 3X, 5X, 7X and 10X. Copyright 2020 Leaf Group Ltd. / Leaf Group Media, All Rights Reserved. This tri-fold mirror looks like it came straight out … 2) Ray diagrams are a useful way to help understand how these laws work in magnifying mirrors. 1) Mirrors function according to the laws of physics – in this case the laws of reflection. The power in which the seen image is amplified comes in many strengths, but the ideal for routine and daily care is 7 – 10x. Magnification strength is the most important feature on a magnifying mirror, but there is such a thing as too much. Ans.convex mirror. Substitute the required information into the mirror equation, as follows: 1/4 + 1/D image = 1/6; 1/D image = 1/6 – 1/4 = - (1/12); D image = - 12. 2) Magnifying mirrors are rated for their power of magnification based on how much bigger they make an object look. In the following diagram we are concerned with 3 points, the center of curvature, the focal point and the top of an object. The image is upright and three times larger than the object. 4) A poorer quality mirror may show some distortion or waviness that will affect its usefulness. Hence it is a concave mirror. As the object is always above the principal axis, the height of the object is always positive. Perhaps if the user’s vision is declining a bit or if they are doing very detailed work a 7X mirror would be appropriate. In a concave mirror, the magnification is the ratio of the height of the image to the height of the object. 1) The amount of magnification is determined by two factors; What will be the distance of the object, when a concave mirror produces an image of magnification m? Magnification is also equal to the ratio of image distance to the object distance. Note that its large magnitude helps spread out the reflected energy. 2) Using some high school algebra you can arrive at the data for this table (dimensions are in millimeters and numbers have been rounded). Never use abrasives or scouring pads. b. c. The two lines intersect at a point behind the mirror which is the top of the image. Hence, the expression for magnification (m) becomes: m = h’/h = -v/u. Once you have a mirror follow the manufacturer’s instructions for cleaning and maintaining it. Study the following equation, called the “mirror magnification equation," which relates the height of the image (H image), the height of the object (H object), D image and D object: M = H image/H object = - (D image/D object). It is the ratio of the height of the image to the height of the object and is denoted as m. The magnification, mproduced by a spherical mirror can be expressed as: Here, h is the height of image and h’is the height of the object. Study the following equation, called the "mirror equation," which relates the distance of an object (D object), the distance of the image (D image) and the focal length (F) of the mirror: 1/D object + 1/D image = I/F. The formula for magnification is = height of image / height of object = -1. Substitute the required information into the mirror magnification equation, as follows: M = - (D image/D object) = - (- 12/4) = 3. For glass mirrors use a soft, damp cloth and, if necessary a little mild detergent or glass cleaner (like Windex). For this reason, concave mirrors are classed as spherical mirrors. Merry has an extensive background in chemical and metallurgical research, physics, nuclear radiation analysis, and associated technologies. When objects are positioned between the focal point of a concave mirror and the mirror's surface, or the vertex, the images seen are “virtual”, upright and magnified. a. R is the radius of the curved surface of the glass When choosing a mirror, check the quality of the reflection and then decide if the magnification meets your needs. Because it’s on the back side of the mirror where you can’t actually see it it’s called a virtual image, 3) So let’s look at a ray diagram. The image is a virtual image, not a real image: it “appears” to be located 12 inches behind the mirror, hence the negative sign. The mirror must be a spherical mirror (concave mirror) as the magnification in plane mirror is never -1 but always 1. Michael holds a Bachelor of Technology from Ryerson University. e. H1 is the height of its reflection 2) The complex explanation is that there is a lot of physics and math behind the magnification. f. D1 is the distance of the reflection from the face of the mirror For this reason, concave mirrors are classed as spherical mirrors. Find the magnification of the heater element in Example 1. When objects are positioned between the focal point of a concave mirror and the mirror's … 1) The simple explanation is that because the curvature of the mirror reflects light at an angle the reflected image is magnified. What is the focal length of a makeup mirror that produces a magnification of 1.50 when a person’s face is 12.0 cm away? The focal length of a mirror is the distance to the focal point, which is the point midway between the geometric center or vertex of the mirror and the center of curvature of the mirror. Therefore the type of mirror … For plastic or other mirror materials refer to the manufacturer’s directions. A Toronto native, Michael Merry began writing on health and fitness in 2010. There is a formula for the magnification but, unfortunately, it is not always applied correctly. Jerdon Tri-Fold Two-Sided Lighted Makeup Mirror. 2/3=0.6.. i.e m is smaller than 1, hence is diminished and is positive and hence the image is virtual. The magnification of a spherical mirror image can be determined, analytically, if either the focal length or center of curvature of the mirror is known. Remember that some of the finishes on other parts of the mirror are not as damage resistant as glass and treat them accordingly. A plain flat mirror would be rated at 1X and one that makes an object 3 times larger would be rated at 3X. d. D0 is the distance of the object from the center of the mirror g. M is the magnification of the mirror A plain flat mirror would be rated at 1X and one that makes an object 3 times larger would be rated at 3X. 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. Our two light rays behave as follows: Magnification is the increase in the image size produced by spherical mirrors with respect to the object size. 5) Because its surface is harder and not as easily damaged a glass mirror will provide longer life than a plastic mirror and most metal mirrors. For this reason, concave mirrors are classed as spherical mirrors. A virtual mirror image is an image from which rays of reflected light appear to diverge.