1).What is the speed of light in vacuum.
i. 3×10 km/s
ii. 2.25 x10 m/s
iii. 3×10 m/s
iv. 3×10 cm/s
Ans: iii. 3×10 m/s
2). Which colour of light has the highest speed in a medium?
i. blue
ii. Violet
iii. Orange
iv.Red
Ans: iv.Red
3). Absorption of which ray causes hotness?
i. UV rays
ii. Infrared ray
iii. X-ray
iv. Gamma ray
Ans: ii. Infrared ray
4). Which of the following is the best refracting transparent medium?
i. glycerine
ii. Water
iii. Glass
iv. Iron
Ans: iii. Glass
5).Which of the following is the refractive index of water?
i. 1.33
ii.1.36
iii. 1.47
iv. 1.56
Ans: i. 1.33
6).Which of the following is the critical angle of glass?
i. 50°
ii. 46°
iii. 49°
Iv. 42°
Ans: Iv. 42°
7). Which of the following has maximum refractive index?
i. Glycerine
ii. Diamond
iii. Paraffin
iv. Water
Ans: ii. Diamond
8).Which of the following images can be formed by a convex lens?
i. Virtual and diminished
ii. Erect but of the same size
iii. Virtual and magnified
iv. Virtual but of the same size
Ans: iii. Virtual and magnified
9).What is the power of lens having focal length of -2D?
i. -2m
ii. 0.5 m
iii. -0.55 cm
iv.-0.5 m
Ans: i. -2m
10).On which of the following parts, is the image formed?
i. pupil
ii. Iris
iii. Retina
iv. Cornea
Ans: iii. Retina
11).Which of the following is the characteristic of the image formed by a concave lens?
i. real and magnified
ii. Real and diminished
iii. Virtual and magnified
iv. virtual and diminished
Ans: iv. virtual and diminished
12).If a convex lens forms a virtual and magnified image, where is the object kept?
i. at 2 F f.
ii. at infinity
iii. between F and 2 F
iv. Between optical centre and F
Ans:iii. between F and 2 F
13). What is the power of a convex lens of focal length 25 cm?
i. 25D
ii. 0.25 D
iii. 4 D
iv. 0.04 D
Ans: iii. 4 D
14).Which lens is thicker at the middle and thinner at its edges?
i. concave convex
ii. concave lens
iii. concave plane
iv. Convex concave
Ans: iv. Convex concave
15. Differentiate between:
a. Reflection and refraction of light
| Reflection of light | Refraction of light |
| Reflection is like a bounce-back of light when it hits a surface and goes back in the same direction. | Refraction is when light changes its direction and speed as it passes through a different material, like going from air into water. |
| Reflection keeps light on the same side of the surface it hits, just bouncing off at an angle. | Refraction causes light to change direction and sometimes speed, moving to a different angle inside the new material. |
| Reflection allows us to see images of objects or ourselves in mirrors or shiny surfaces. | Refraction can make objects appear distorted or shifted when you look through a glass of water or a lens. |
b. Refraction and total internal reflection of light
| Refraction of light | Total internal reflection of light |
| Refraction happens when light bends as it moves from one substance to another, like from air to water. | Total internal reflection occurs when light is completely reflected back into the same material instead of passing through to the other side. |
| It’s like light changing its path or direction when passing through different materials. | This happens when light tries to move from a denser material (e.g., water) to a less dense material (e.g., air) at a steep angle. |
| Refraction involves light changing its path and bending either towards or away from the normal line, depending on the materials it’s passing through. | Total internal reflection causes light to stay within the original material, bouncing back instead of crossing into another material. |
c. Refractive index and critical angle
| Refractive index | Critical angle |
| Refractive index tells us how much a substance can bend or slow down light when it passes through it. | The critical angle is a specific angle at the boundary between two materials where light can just barely stay inside the denser material and doesn’t cross into the less dense one. |
| Refractive index is about how much a material can bend light. Higher refractive index means more bending of light, like in diamonds. | Critical angle is about when light bends to the maximum but doesn’t cross over, especially from denser to less dense material. |
| Refractive index is widely used to design lenses, glasses, and optical instruments. | Critical angle is vital for understanding phenomena like total internal reflection, which is the basis for fiber optics and other applications. |
d. Rarer and denser mediums
| Rarer mediums | Denser mediums |
| Rarer mediums are substances that are not very tightly packed, like air or gases. | Denser mediums are materials where the particles are closely packed together, like water or glass. |
| Light can move faster through rarer mediums due to the ample space between particles allowing for quicker travel. | In denser mediums, light slows down a bit because it has to navigate through the closely packed particles. |
| When light moves from a rarer to a denser medium, it tends to bend towards the normal (an imaginary line perpendicular to the surface). | Conversely, when light moves from a denser to a rarer medium, it bends away from the normal. |
e. Concave and convex lenses
| Concave lens | Convex lens |
| A concave lens is thin in the middle but thicker at the edges, resembling a curved spoon. | A convex lens is thicker in the middle and thinner at the edges, like a magnifying glass. |
| Concave lenses make light rays spread out or diverge, as if the light is moving away from a common point. | Convex lenses make light rays converge, bending them towards a focal point, like gathering them at a single point. |
| Concave lenses are often used to correct short-sightedness and help people see distant objects more clearly. | Convex lenses find uses in magnifying glasses, glasses for farsightedness, and in cameras to focus light and form clear images. |
f. Near and far points
| Near Point | Far point |
| The near point is the closest distance at which our eyes can focus on an object clearly without any strain. | The far point is the farthest distance at which our eyes can focus on an object clearly without any strain. |
| It’s like the shortest distance our eyes can comfortably read a book or see things up close. | Imagine it as the maximum distance where our eyes can clearly see a distant mountain or a road sign. |
| Near point demonstrates how well our eyes can focus on nearby objects, allowing us to comfortably read, write, or work up close. | Far point illustrates our eyes’ ability to focus on objects at a distance, essential for activities like watching a game or identifying faraway objects. |
g. Myopia and hypermetropia
| Myopia | Hypermetropia |
| Myopia, or nearsightedness, means you can clearly see nearby objects but struggle with distant ones. | Hypermetropia, or farsightedness, is the opposite. You can see distant objects more clearly than things up close. |
| Imagine being able to read a book easily but having difficulty seeing a clear view of the chalkboard. | Picture being able to see road signs clearly but finding it hard to read a book comfortably. |
| Myopia occurs when the eyeball is a bit too long or the cornea (front part of the eye) is too curved, causing light to focus in front of the retina. | Hypermetropia happens when the eyeball is shorter than usual or the cornea is too flat, causing light to focus behind the retina. |
h. Cataract and night blindness
| Cataract | Night blindness |
Cataract is like having a cloudy window in your eye. It happens when the lens in your eye becomes cloudy, making everything you see appear blurry or foggy. | Night blindness is when it’s hard to see clearly in low light or at night. It’s like your eyes struggle to adjust when it’s dark. |
| Cataract is mainly caused by aging, injury, or certain medical conditions that make the lens in your eye cloudy. | Night blindness can be due to a deficiency in vitamin A or certain eye conditions affecting the cells in your retina that help you see in low light. |
| Imagine looking through a misty glass – things get hazy and unclear. | Picture trying to find something in a dimly lit room – you might have trouble seeing the details. |
16).State the laws of refraction of light.
Ans:The law of refraction, also known as Snell’s Law, states that the ratio of the sine of the angle of incidence to the sine of the angle of refraction is constant when a light wave passes from one medium to another.
17). Why does light bend when it passes from one medium to another?
Ans:Light bends or changes direction when it goes from one medium (like air) to another (like water) because different medium make light move at different speeds.
18).Define dispersion of light.
Ans:Dispersion of light means that light is split into its different colors, creating a spectrum.
19).Define critical angle.
Ans: The critical angle is the specific angle at which light, traveling from a denser to a less dense material, will be completely reflected instead of refracted.
20). What is the value of the critical angle of diamond?
Ans: The critical angle of diamond is approximately 24.4 degrees.
21).Define refractive index.
Ans: Refractive index is a measure that tells us how much a substance can bend or change the direction of light as it passes through it, compared to the speed of light in a vacuum.
22).What is the relation of refractive index and speed of light in medium?
Ans: The refractive index of a medium is a measure of how much slower light travels through that medium compared to its speed in a vacuum.
23). What is optical fibre?
Ans: An optical fiber is a very thin and flexible thread made of glass or plastic. It can transmit light signals over long distances, helping to send information like internet, phone calls, and data quickly and efficiently.
24).Define light pipe.
Ans: A light pipe is a transparent tube or channel that guides and transmits light from one place to another, often used to transport natural or artificial light for illumination in buildings or devices.
26). Define the following.
i. refraction of light
Refraction of light is when light changes its direction and speed as it passes from one material into another.
ii. Total internal reflection
Total internal reflection happens when light inside a medium is completely reflected back at the boundary of that medium because it’s trying to leave and enter a less dense material, like air.
iii. critical angle
The critical angle is a specific angle at the boundary between two materials. If light strikes this boundary at an angle greater than the critical angle, it will be reflected back into the denser medium instead of passing through into the less dense medium.
iv. dispersion of light
Dispersion of light occurs when light is separated into its different colors, like a rainbow. This happens because different colors of light bend by different amounts when passing through a material like a prism, which separates the light into its various colors based on their wavelengths.
27). Mention the conditions required for total internal reflection.
Ans:Total internal reflection occurs when light tries to leave a denser medium and enter a less dense medium, and the angle at which it’s trying to leave is greater than the critical angle for that boundary.
28). What is of use of total internal reflection in our daily life?
Ans:Total internal reflection is used in various everyday applications, including:
Optical Fibers: Transmitting data (internet, phone calls) through thin glass fibers using total internal reflection.
Prism Binoculars: Allowing us to see distant objects clearly and in a compact design.
Diamond Cutting: Enhancing the sparkle and brilliance of diamonds by exploiting total internal reflection within the diamond.
29). Describe looming in short with a diagram.
Ans: Looming is when something looks taller or higher than it actually is because of the way light bends in the air.
Object: Representation of an object (e.g., a building or a ship).
Warm Air Layer: Depiction of the warm air close to the ground.
Cooler Air Layer: Representation of the cooler air above the warm air.
Light Rays: Arrows showing the bending of light rays due to the change in air temperature, creating the looming effect and making the object appear taller.
30). Enlist any four events that are caused due to refraction of light.
Ans: Any four events that are caused due to refraction of light are:
1. Bending of a Straw in a Glass
2. Apparent Shifting of a Fish in Water
3. Broken Pencil in Water
4. Mirage on a Hot Day
31). Do sound waves show the properties of light waves? Justify your answer giving examples.
Ans: Sound waves and light waves have similarities, like frequency and wavelength, but they also have key differences. Sound waves need a medium to travel (like air or water), while light waves can travel through a vacuum. Sound waves are longitudinal, while light waves are transverse.
32). Describe in short the use of optic fibres in information and communication sector.
Ans: Optic fibers are extensively used in the information and communication sector to transmit data at high speeds over long distances. They are crucial for internet connectivity, phone calls, and television signals. For instance, when you use the internet to browse websites or stream videos, optic fibers play a key role in ensuring a fast and smooth connection.
33). What is myopia?
AnMyopia, often called nearsightedness, is an eye condition where distant objects appear blurry, but nearby objects can be seen clearly.
34). Which lens is used to correct hypermetropia?
Ans:A lens known as a converging or convex lens is used to correct hypermetropia.
35). In which defect of vision is eye ball flattened?
Ans: The eye condition where the eyeball is flattened is known as myopia or nearsightedness.
36). What is cataract?
Ans: Cataract is a condition in the eye where the natural lens becomes cloudy or opaque, leading to blurred or hazy vision.
37). Deficiency of which vitamin causes night blindness?
Ans: Deficiency of vitamin A causes night blindness.
38). In which disease, the victim cannot identify red and green color?
Ans: The disease where the victim cannot identify red and green colors is known as color blindness.
39). What is the function of the retina?
Ans:The retina’s function is to capture light and convert it into electrical signals, which are then sent to the brain for interpretation, allowing us to see and perceive the visual world.
40). Define focal length.
Ans: Focal length is the distance between the center of a lens or a curved mirror and the point where light rays converge or diverge to/from a single point.
41).What is principal focus?
Ans: The principal focus is a specific point on the optical axis of a lens or mirror where parallel rays of light either converge or appear to converge after refraction or reflection, respectively.
42).Define spectrum.
Ans: A spectrum is a band of colors or a range of different but related things, like colors of light or sound frequencies, arranged in a particular order.
43). What is dispersion of light?
Ans: Dispersion of light is the process where light, which appears white, is separated into its different colors (like a rainbow) when it passes through a medium like a prism. This happens because each color of light bends by a slightly different amount due to its specific wavelength, resulting in the visible spectrum of colors.
44).What is the ray found above the red colour in the spectrum?
Ans: The ray found above the red color in the spectrum is called infrared.
46). Write the formula for the power of lens and magnification of lens each.
Ans:Formula for the Power of Lens:
The formula for the power of a lens (P) is given by:
P= 1/f
Formula for Magnification of Lens:
The formula for the magnification (M) of a lens is given by:
M= -v/u
where is thhe image distance and u is the object distance .
47). A convex lens forms a real image of the same size as that of the object. Where is the object placed? Draw a ray diagram.
Ans: To form a real image of the same size as the object with a convex lens, the object must be placed at twice the focal length (2f) from the lens.
47). How is the amount of light controlled when it enters into the eye?
Ans: The amount of light entering the eye is controlled by the pupil. The pupil is like a small adjustable hole in the center of the colored part of the eye (iris). It can change its size to regulate the amount of light entering the eye. In bright light, the pupil becomes smaller to let in less light, and in dim light, it enlarges to allow more light to enter. This adjustment helps in maintaining the right amount of light for clear vision.
48).What is myopia? How is it corrected?
Ans: Myopia, also known as nearsightedness, is a condition where distant objects appear blurry, but nearby objects can be seen clearly.
Myopia is usually corrected using concave lenses, which are thinner at the center and thicker at the edges. These lenses help in diverging the incoming light rays slightly before they reach the eye’s lens, allowing the image to be correctly focused on the retina, resulting in clear vision for distant objects.
49). What is hypermetropia? How is it corrected?
Ans:Hypermetropia, also known as farsightedness, is a condition where nearby objects appear blurry, but distant objects can be seen relatively clearly.
Hypermetropia is usually corrected using convex lenses, which are thicker at the center and thinner at the edges. These lenses help in converging the incoming light rays slightly before they reach the eye’s lens, allowing the image to be correctly focused on the retina, resulting in clear vision for nearby objects.
52). Sheetal wears a lens of power +2 D. Answer the following questions
i. What is the defect of Sheetal’s vision called?.
Ans: Sheetal’s vision defect is hypermetropia or farsightedness.
ii. How is it corrected by using a lens?
Ans: Hypermetropia is corrected using a converging lens, also known as a convex lens.
iii. What causes this type of defect?
Ans:Hypermetropia is caused when the eyeball is too short or the cornea is too flat, leading to the image being focused behind the retina instead of on it.
iv. How does she manage a newspaper while reading without using the lens? Why?
Ans: Sheetal might manage to read a newspaper without using the lens by holding it at a distance where the image is focused on the retina. This is because the lens in the eye can adjust its focal length slightly to bring the image onto the retina for clear vision at a certain distance.
53). A stick partly immersed in water, appears bent.
Ans: When a stick is partly immersed in water and appears bent, it’s due to the way light bends or refracts when it travels from water (a denser medium) to air (a less dense medium) at the surface of the water. This bending of light makes the submerged portion of the stick seem offset or bent from its actual position.
54). The incident light deviates from its rectilinear path as it passes from one medium to another.
Ans: When light passes from one medium to another, it deviates from its straight path due to a change in the speed of light in the different mediums. This change in speed causes the light to change its direction, a phenomenon known as refraction. The degree of deviation depends on the change in the speed of light and the angle at which the light enters the new medium.
55). White light is found to be broken into seven colours after passing through a prism while no such thing takes place when light passes through a glass slab.
Ans: When white light passes through a prism, it gets separated into its seven colors due to a process called dispersion. This happens because a prism causes different colors of light to bend by varying amounts based on their wavelengths.On the other hand, when light passes through a glass slab, it does not get separated into its colors because a glass slab does not cause different colors of light to bend differently or spread out.
56). A swimming pool appears shallower than it real depth.
Ans: A swimming pool appears shallower than its actual depth due to how light bends when it moves from water to air. This bending makes the pool floor seem closer to the surface than it truly is, giving the illusion of reduced depth.
57). If a fish in an aquarium is observed from the bottom, it appears in air.
Ans: When observing a fish in an aquarium from below, it appears in air due to the refraction of light at the water-air interface. The light bends as it passes from water (denser medium) to air (less dense medium), creating an image of the fish that seems to be in a different location.
58). Stars twinkle but planets do not.
Ans: Stars twinkle because their light passes through Earth’s atmosphere, which causes the light to bend and flicker due to varying air density and temperature. Planets, being closer and having a more solid light source, do not exhibit the same twinkling effect as their light is not as affected by the atmosphere.
59). A person hits a spear to a fish at the place where it is seen in water but the fish escapes
Ans: The apparent position of the fish in the water is an optical illusion caused by the bending of light at the water-air interface. The fish is actually at a different, deeper location than it appears, making the spear miss its target when aimed at the illusionary position.
60). In the spectrum of light, violet is found at the bottom and red at the top.
Ans: In the spectrum of light, violet is at the bottom and red is at the top because violet light has a shorter wavelength and higher frequency, causing it to bend or refract more compared to red light when passing through a prism. This results in violet light being deviated more towards the bottom and red light less, positioning them accordingly in the spectrum.
61). A convex lens is called a converging lens.
Ans: A convex lens is called a converging lens because it bends or converges parallel rays of light towards a single point called the focal point when they pass through it.
62). The size of the pupil enlarges at dark.
Ans: The size of the pupil enlarges in the dark because to allow more light to enter the eye.
63). A concave lens is called a diverging lens.
Ans: A concave lens is called a diverging lens because it causes parallel rays of light to spread out or diverge when they pass through it.
64). Convex lens spectacles are used to correct hypermetropia.
Ans: Convex lens spectacles are used to correct hypermetropia because they help converge incoming light rays, allowing the image to be correctly focused on the retina.
65). Concave lens spectacles are used to correct myopia.
Ans: Concave lens spectacles are used to correct myopia because they diverge incoming light rays before they reach the eye’s lens.
66). Convex lens have positive focal length.
Ans:Convex lenses have a positive focal length because they converge light rays. The curvature of a convex lens causes parallel light rays to converge at a point, known as the focal point. This convergence is a characteristic of convex lenses, giving them a positive focal length.
67). A person with myopia cannot see distant object.
Ans: A person with myopia, or nearsightedness, cannot see distant objects clearly because their eyeball is too long or the cornea is too curved. This causes the light entering the eye to focus in front of the retina instead of on it, resulting in a blurry image for distant objects.
68). A person with hypermetropia cannot see closer object.
Ans:A person with hypermetropia, or farsightedness, cannot see closer objects clearly because their eyeball is too short or the cornea is too flat. This causes the light entering the eye to focus behind the retina instead of on it, resulting in a blurry image for nearby objects.
69). Old people have a high of night blindness.
Ans: Older people may experience a higher occurrence of night blindness due to age-related changes in the eyes, such as reduced ability to adjust to low light conditions. The retina, which is crucial for night vision, may become less sensitive, making it difficult to see clearly in low-light situations like at night. This can lead to a higher incidence of night blindness in older individuals.
70). Cows and buffaloes are colour blind.
Ans: Cows and buffaloes are considered color blind because they have a limited number of color receptors (cones) in their eyes.
71). The pupil of the eye is changeable in size.
Ans:The pupil of the eye can change its size due to the action of the iris, a muscular structure.
72).The pupil of the eye enlarges in dark.
Ans: The pupil of the eye enlarges in the dark to allow more light to enter the eye. This dilation, controlled by the iris muscles, helps maximize the amount of light reaching the retina, enhancing vision and visibility in low light conditions.
73). The ciliary muscle is important for vision.
Ans: The ciliary muscle is vital for vision because it controls the shape and curvature of the lens in the eye.
