Welcome to the world of light and its fascinating behavior! In this comprehensive set of 10th-class Physics notes, we delve into the captivating realm of Geometrical Optics, the twelfth unit of study. Within this unit, we embark on a journey through the principles that govern the propagation of light, exploring its reflection, refraction, and the formation of images by lenses and mirrors. Whether you’re a curious student seeking a deeper understanding of how light interacts with the world around us or a dedicated educator looking to enhance your teaching resources, these notes will illuminate the complexities of Geometrical Optics and shed light on its practical applications in our daily lives. So, let’s begin this enlightening voyage into the realm of optics and uncover the secrets of light’s path through space.
10th Physics Unit 12 Long Question Notes
10th Physics Unit 12 MCQ’s Long Question Notes
10th Physics Unit 12 Numerical Notes
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10th Physics Unit 12 Short Question Notes
Define reflection of light.
Answer: Reflection of light is the phenomenon where a ray of light, when incident on the surface of another medium, turns back in the same medium.
What are the laws of reflection?
Answer: The laws of reflection are:
(i) The incident ray, the normal, and the reflected ray at the point of incidence all lie in the same plane.
(ii) The angle of incidence is equal to the angle of reflection, i.e., i = r.
What are the two types of reflection based on the smoothness of the surface?
Answer: The two types of reflection based on the smoothness of the surface are regular reflection and irregular reflection.
What is the difference between a concave mirror and a convex mirror?
Answer: A concave mirror has a reflecting inner curved surface and can form both virtual and real images. On the other hand, a convex mirror has a reflecting outer curved surface and can only form virtual and erect images, which are always smaller than the object.
Define the principal focus of a spherical mirror.
Answer: The principal focus of a spherical mirror is the point where light rays parallel to the principal axis converge (in the case of a concave mirror) or appear to diverge from (in the case of a convex mirror) after reflection.
What is the focal length of a spherical mirror and how is it related to the radius of curvature?
Answer: The focal length (f) of a spherical mirror is the distance from the pole to the principal focus measured along the principal axis. It is related to the radius of curvature (R) by the formula f = R/2.
Describe how light is reflected by a concave mirror and a convex mirror.
Answer: In a concave mirror, light rays parallel to the principal axis converge to the principal focus after reflection. In a convex mirror, light rays parallel to the principal axis appear to come from the principal focus after reflection (though they do not actually pass through it).
What is the nature of the image formed by a convex mirror?
Answer: The image formed by a convex mirror is always virtual, erect, and smaller in size than the object.
What is the phenomenon of physics involved when you see the image of a lion formed inside the pond water?
Answer: The phenomenon involved is the refraction of light. Light rays change direction as they pass from air into water due to the change in the speed of light, causing the image of the lion to appear displaced.
What is the refractive index of a medium?
Answer: The refractive index of a medium is the ratio of the speed of light in air to the speed of light in the medium.
How can we find the angle of refraction when light passes from air to glass?
Answer: Using Snell’s law, we can find the angle of refraction. The formula is: refractive index of glass = sin(angle of refraction)/sin(angle of incidence).
What is total internal reflection?
Answer: Total internal reflection occurs when a ray of light traveling in a denser medium (e.g., glass) strikes the boundary with a rarer medium (e.g., air) at an angle greater than the critical angle. The entire light is reflected back into the denser medium with no refraction.
What is the critical angle?
Answer: The critical angle is the angle of incidence in the denser medium that causes the refracted ray in the rarer medium to bend through 90 degrees.
When does total internal reflection occur?
Answer: Total internal reflection occurs when the angle of incidence in the denser medium is greater than the critical angle, i.e., when the light is striking the boundary with a rarer medium at an angle larger than the critical angle.
What is the main principle behind the functioning of a totally internal reflecting prism?
Answer: Total internal reflection is the main principle behind the functioning of a totally internal reflecting prism.
Why is total internal reflection possible in a right-angled prism?
Answer: Total internal reflection is possible in a right-angled prism because the angle of incidence of light on the prism is greater than the critical angle of the glass.
What is the angle of incidence when a ray of light strikes a face of the prism perpendicularly?
Answer: The angle of incidence is 45 degrees when a ray of light strikes a face of the prism perpendicularly.
How much is the total deviation when a ray of light is totally reflected by the prism?
Answer: The total deviation when a ray of light is totally reflected by the prism is 90 degrees.
Which optical instruments use totally internal reflecting prisms for reflection?
Answer: Cameras, binoculars, periscopes, and telescopes are some of the optical instruments that use totally internal reflecting prisms for reflection.
How is total internal reflection used in fiber optics?
Answer: Total internal reflection is used in fiber optics to transmit light signals over long distances with minimal energy loss.
What are the two main parts of an optical fiber?
Answer: The two main parts of an optical fiber are the core (made of high refractive index glass or plastic) and the cladding (made of low refractive index glass or plastic).
Why is an endoscope considered a useful medical instrument?
Answer: An endoscope is considered a useful medical instrument because it allows exploratory diagnostics and surgical procedures without invasive surgery. It can be inserted through natural body openings.
What is the angle of deviation when light passes through a triangular glass prism?
Answer: The angle of deviation is the angle by which the emergent ray is deviated from its original path after passing through the prism.
How is the focal length of a convex lens determined?
Answer: The focal length of a convex lens can be determined by placing it in front of a white screen and adjusting its position until a sharp image of a distant object is obtained on the screen. The distance between the lens and the screen is the approximate focal length.
What is the power of a lens defined as?
Answer: The power of a lens is defined as the reciprocal of its focal length in meters.
What is the SI unit of the power of a lens?
Answer: The SI unit of the power of a lens is the “Dioptre” (D), which is equal to 1 m^(-1).
Is the power of a convex lens positive or negative? What about a concave lens?
Answer: The power of a convex lens is positive, whereas the power of a concave lens is negative.
How are images formed in lenses? What type of images do convex lenses form?
Answer: Images in lenses are formed through refraction. Convex lenses form real and inverted images when the object is placed beyond 2F, real and erect images when the object is between F and 2F, and virtual and magnified images when the object is inside the focal length.
What are the three principal rays used in the ray diagram for image formation by a convex lens?
Answer: The three principal rays are:
- Ray parallel to the principal axis, which passes through the focal point after refraction.
- Ray passing through the optical center, which remains undeviated.
- Ray passing through the focal point, which becomes parallel to the principal axis after refraction.
What happens when dealing with diverging lenses? What should be considered?
Answer: When dealing with diverging lenses, one must be careful not to omit the negative sign associated with the focal length and the image position.
What are the sign conventions for focal length, object distance, and image distance of lenses?
Answer: Focal length (f): Positive for a converging lens, negative for a diverging lens.
Object distance (p): Positive for a real object on the left side of the lens, negative for a virtual object on the right side of the lens.
Image distance (q): Positive for a real image formed on the right side of the lens, negative for a virtual image formed on the left side of the lens.
Define the lens formula and state when it is valid.
Answer: The lens formula relates the object distance (p), the image distance (q), and the focal length (f) of a lens. It is valid for both concave and convex lenses.
How can you determine the size and nature of an image formed by a lens for a given object distance?
Answer: The lens formula can be used to determine the image distance, and with that information, the nature of the image (real or virtual) can be determined. The size of the image can be found using the magnification formula (magnification = image height / object height).
A camera uses a convex lens with a focal length of 0.05 m. If a person 1.7 m tall stands 2.5 m in front of the camera, find the image distance and determine whether the image is real or virtual.
Answer: The image distance is 19.6 m and the image is real.
What is the application of lenses in a camera?
Answer: Lenses in a camera focus images onto the film, producing real, inverted, and diminished images. The distance between the lens and film is fixed and equal to the focal length of the lens.
How does a slide projector work?
Answer: In a slide projector, a light source is placed at the center of curvature of a concave mirror, which reflects light back in parallel rays. The condenser, consisting of two converging lenses, refracts the light to illuminate all parts of the slide with parallel rays.
What is the principle of a photograph enlarger?
Answer: A photograph enlarger uses a convex lens to produce a real, magnified, and inverted image of the film on photographic paper. The object is placed at a distance greater than the focal length but less than twice the focal length of the lens.
What is the magnifying glass, and how does it work?
Answer: A magnifying glass is a convex lens used as a simple microscope. It forms an upright, virtual, and magnified image when the object is placed nearer to the lens than the principal focus, making the object appear larger.
How is the magnifying power of a magnifying glass calculated?
Answer: The magnifying power of a magnifying glass is given by the formula: Magnifying Power (M) = 1 + (distance of the near point of the eye / focal length of the lens).
What is the resolving power of an optical instrument?
Answer: The resolving power of an instrument is its ability to distinguish between two closely placed objects or point sources.
How does a compound microscope work?
Answer: A compound microscope consists of two converging lenses, the objective, and the eyepiece. The objective lens forms a small real image, which acts as an object for the eyepiece to produce a larger virtual image that is viewed by the eye.
What is the magnification formula for a compound microscope?
Answer: The magnification (M) of a compound microscope is given by: Magnification (M) = (Length of compound microscope / Distance of final image from the eye) = (fo + fe) / fe, where fo is the focal length of the objective lens, and fe is the focal length of the eyepiece.
How does a refracting telescope work?
Answer: A refracting telescope uses two converging lenses, the objective, and the eyepiece. The objective lens forms a real image of the distant object, while the eyepiece forms a virtual image that is viewed by the eye.
What is accommodation in the human eye?
Answer: Accommodation is the ability of the eye to adjust the focal length of its lens to focus on objects at different distances, providing clear images on the retina. The ciliary muscles control the curvature of the lens to achieve accommodation.
What are the near point and far point of the human eye?
Answer: The near point is the minimum distance from the eye at which an object produces a sharp image on the retina. The far point is the maximum distance at which a distant object can be focused on the retina with a fully relaxed eye. For normal vision, the far point is at infinity, and the near point is about 25 cm from the eye.
What is a defect of vision?
Answer: The inability of the eye to see the image of objects clearly.
What is the common name for nearsightedness?
Answer: Nearsightedness is also known as myopia.
What causes nearsightedness?
Answer: Nearsightedness may be due to the eyeball being too long, causing light rays from distant objects to focus in front of the retina.
How can nearsightedness be corrected?
Answer: Nearsightedness can be corrected with glasses or contact lenses that use diverging lenses.
What is farsightedness also known as?
Answer: Farsightedness is also known as hypermetropia.
How does farsightedness affect the formation of images on the retina?
Answer: Farsightedness causes the eye to form blurred images of nearby objects, as the focal length is longer than it should be.
How can farsightedness be corrected?
Answer: Farsightedness can be corrected with the aid of a suitable converging lens, which refracts light rays to converge and form an image on the retina.
What special ability do some animals, like fish, have with their eye lenses?
Answer: Some animals, like fish, can move their eye lenses forward or backward, enabling them to see objects around them clearly.
How can the glare of reflected light be prevented with eyeglasses?
Answer: A thin film can be placed on the lenses of eyeglasses to prevent the reflection of highly visible wavelengths of light, reducing glare.
Where is the image formed in a corrected nearsighted eye?
Answer: In a corrected nearsighted eye, the image is formed on the retina.