EXAMPLE 25-6 Nearsighted eye. A nearsighted eye has near and far points of 12 cm and 17 cm, respectively. (a) What lens power is needed for this person to see distant objects clearly, and (b) what then will be the near point? Assume that the lens is 2.0 cm from the eye (typical for eyeglasses). APPROACH For a distant object (d, = 0), the lens must put the image at the far point of the eye as shown in Fig. 25–14a, 17 cm in front of the eye. We can use the thin lens equation to find the focal length of the lens, and from this its lens power. The new near point (as shown in Fig. 25–14b) can be calculated for the lens by again using the thin lens equation. SOLUTION (a) For an object at infinity (d, = 0), the image must be in front of the lens 17 cm from the eye or (17 cm – 2 cm) = 15 cm from the lens; hence d; = -15 cm. We use the thin lens equation to solve for the focal length of the O 2 cm Object at oo I•<= 17 cm- (Far point) (a) needed lens: 1 1 + do 1 12 cm - (Near point) di -15 cm 15 cm So f = -15 cm = -0.15 m or P = 1/f = -6.7 D. The minus sign indicates that it must be a diverging lens for the myopic eye. (b) The near point when glasses are worn is where an object is placed (d.) so that the lens forms an image at the "near point of the naked eye," namely 12 cm from the eye. That image point is (12 cm – 2 cm) = 10 cm in front of the lens, so d; = -0.10 m and the thin lens equation gives (b) FIGURE 25-14 Example 25–6. 1 1 0.30 m 1 1 1 1 -2 + 3 d. di 0.15 m 0.10 m 0.30 m So d, = 30 cm, which means the near point when the person is wearing glasses is 30 cm in front of the lens, or 32 cm from the eye.
Ray Optics
Optics is the study of light in the field of physics. It refers to the study and properties of light. Optical phenomena can be classified into three categories: ray optics, wave optics, and quantum optics. Geometrical optics, also known as ray optics, is an optics model that explains light propagation using rays. In an optical device, a ray is a direction along which light energy is transmitted from one point to another. Geometric optics assumes that waves (rays) move in straight lines before they reach a surface. When a ray collides with a surface, it can bounce back (reflect) or bend (refract), but it continues in a straight line. The laws of reflection and refraction are the fundamental laws of geometrical optics. Light is an electromagnetic wave with a wavelength that falls within the visible spectrum.
Converging Lens
Converging lens, also known as a convex lens, is thinner at the upper and lower edges and thicker at the center. The edges are curved outwards. This lens can converge a beam of parallel rays of light that is coming from outside and focus it on a point on the other side of the lens.
Plano-Convex Lens
To understand the topic well we will first break down the name of the topic, ‘Plano Convex lens’ into three separate words and look at them individually.
Lateral Magnification
In very simple terms, the same object can be viewed in enlarged versions of itself, which we call magnification. To rephrase, magnification is the ability to enlarge the image of an object without physically altering its dimensions and structure. This process is mainly done to get an even more detailed view of the object by scaling up the image. A lot of daily life examples for this can be the use of magnifying glasses, projectors, and microscopes in laboratories. This plays a vital role in the fields of research and development and to some extent even our daily lives; our daily activity of magnifying images and texts on our mobile screen for a better look is nothing other than magnification.
About how much longer is the nearsighted eye in
Example 25–6 than the 2.0 cm of a normal eye?
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