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All questions of Light for Class 7 Exam

Following conditions are true for virtual image
  • a)
    it is always erect
  • b)
    it is formed behind the mirror
  • c)
    it can not be obtained on screen
  • d)
    all the above conditions 
Correct answer is option 'D'. Can you explain this answer?

Geetika Shah answered
a) The virtual image is always erect. The common example of virtual image is the image formed in the mirror when we stand in front of that mirror. 
b) In reality, these rays come from the points on the mirror where they are reflected. The image behind the mirror is called a virtual image because it cannot be projected onto a screen—the rays only appear to originate from a common point behind the mirror.
c) Virtual images cannot be obtained on the screen because the image formed is from the light rays that do not meet but appear to meet when they are produced backwards. 
 
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A magnifying glass is nothing but
  • a)
    concave mirror
  • b)
    convex lens
  • c)
    concave lens
  • d)
    convex mirror 
Correct answer is option 'B'. Can you explain this answer?

Amit Sharma answered
A magnifying glass is a convex lens that is used to produce a magnified image of an object. The lens is usually mounted in a frame with a handle. A sheet magnifier consists of many very narrow concentric ring-shaped lenses, such that the combination acts as a single lens but is much thinner.

Concave lens always forms
  • a)
    Magnified image
  • b)
    Virtual image
  • c)
    Inverted image
  • d)
    Real image
Correct answer is 'B'. Can you explain this answer?

Niti Singh answered
The images formed by concave lenses are always real are always virtual. ... Show transcribed image text. could be real or virtual; it depends on whether the object distance is smaller or greater than the focal length could be real or virtual, but always real when the object is placed at the focal point.

A substance which transmits most of the light rays incident on it is called
  • a)
    transparent
  • b)
    translucent
  • c)
    opaque
  • d)
    none of these 
Correct answer is option 'A'. Can you explain this answer?

Ujwal Sharma answered
Transparent Substances

Transparent substances are materials that allow light to pass through them without scattering the light. They transmit most of the light rays incident on them. The light waves pass through transparent substances in a straight line, making the objects behind them visible. Examples of transparent substances include clear glass, air, and water.

Properties of Transparent Substances

The following are the properties of transparent substances:

- They allow light to pass through them without scattering.
- They transmit most of the light rays incident on them.
- They are clear and can be seen through.
- They do not block the view of objects behind them.
- They do not change the direction of light rays passing through them.

Examples of Transparent Substances

The following are examples of transparent substances:

- Clear glass
- Water
- Air
- Perspex
- Diamond
- Acrylic

Uses of Transparent Substances

Transparent substances have several uses, including:

- Making lenses for eyeglasses, cameras, and telescopes
- Making windows for buildings and vehicles
- Making protective screens and barriers
- Making display cases for museums and shops
- Making bottles and jars for storing liquids

Conclusion

Transparent substances are materials that allow light to pass through them without scattering the light. They transmit most of the light rays incident on them, making them clear and visible. Examples of transparent substances include clear glass, air, and water. They have several uses, including making lenses, windows, and protective screens.

The optical phenomena, twinkling of stars, is due to         
  • a)
    Atmospheric reflection         
  • b)
    Total reflection         
  • c)
    Atmospheric refraction         
  • d)
    Total refraction
Correct answer is option 'C'. Can you explain this answer?

Kunal Khanna answered
Explanation:

The twinkling of stars is an optical phenomenon that occurs due to atmospheric refraction. The light coming from the stars passes through the layers of the Earth's atmosphere, which has varying densities. This causes the light to bend or refract at different angles, making the stars appear to twinkle or flicker.

Atmospheric Refraction:

Atmospheric refraction occurs when light passes through a medium of varying densities. The Earth's atmosphere has different layers of gases, each with a different density. When light passes through these layers, it bends or refracts due to the change in density. The amount of refraction depends on the angle at which the light enters the atmosphere. The lower the angle, the more the light is refracted.

Twinkling of Stars:

The twinkling of stars occurs because stars are very far away from the Earth and their light has to pass through a lot of atmosphere before reaching our eyes. As the light passes through the different layers of the atmosphere, it gets refracted in different directions. This causes the light to scatter, making the stars appear to twinkle or flicker.

Conclusion:

In conclusion, the twinkling of stars is due to atmospheric refraction. The light from the stars passes through the Earth's atmosphere and gets refracted in different directions, causing the stars to twinkle. This phenomenon can be observed on clear nights when the atmosphere is not turbulent.

Which of the following is transparent?
  • a)
    stone
  • b)
    wood
  • c)
    ground glass
  • d)
    plastic 
Correct answer is option 'C'. Can you explain this answer?

Vaibhav Nambiar answered
Transparent Materials

Transparent materials allow light to pass through them without scattering or diffusing the light. Light travels through transparent materials in straight lines, allowing objects behind the material to be clearly seen. Some examples of transparent materials include:

- Glass
- Clear plastic
- Water
- Air

Answer Explanation

Among the given options, only ground glass is transparent. While stone and wood are opaque, plastic may or may not be transparent depending on its type and thickness. Ground glass is a type of glass that has been finely crushed or powdered and then etched to give it a frosted appearance. While it is not completely clear like regular glass, it is still transparent enough to allow some light to pass through it.

Which colour of light scattered least
  • a)
    Green
  • b)
    Yellow
  • c)
    Red
  • d)
    Blue
Correct answer is option 'C'. Can you explain this answer?

Niti Singh answered
Visible light is composed of seven colour having different wavelengths.The molecules of air and other fine particles in the atmosphere have size smaller than the wavelength of visible light and are more effective in scattering light of shorter wavelengths like the blue end than light of longer wavelengths at the red end.The red light has a wavelength about 1.8 times greater than blue light.Thus, when sunlight passes through the atmosphere, the fine particles in air scatter the light of shorter wavelength more strongly than red(having more wavelength).The red is the colour which is least scattered by fog or smoke.Therefore, it can be seen at a distance thats why danger signal lights are red in colour.

In convex mirror, the reflection of light takes place at
  • a)
    Bulging out surface
  • b)
    Bent in surface
  • c)
    Flat surface
  • d)
    An uneven surface
Correct answer is option 'A'. Can you explain this answer?

Palak Rane answered
Reflection of Light in Convex Mirror

Reflection of light takes place at the bulging out surface of a convex mirror.

Explanation:
A convex mirror is a curved mirror that bulges outwards. It is also called a diverging mirror because when parallel rays of light fall on it, they diverge or spread out after reflection. The curvature of the mirror causes the reflection of light to occur at the bulging out surface.

The reflection of light in a convex mirror can be explained using the following points:

1. Curvature of the Mirror:
- The convex mirror has a curved surface that is bulging outwards.
- The curvature of the mirror is such that the center of the mirror is closer to the observer than the edges.
- This curvature is responsible for the reflection of light in the mirror.

2. Incident Light Rays:
- When parallel rays of light fall on a convex mirror, they are incident on the mirror surface.
- These incident rays of light can come from a distant object or a source of light.

3. Reflection at the Bulging Out Surface:
- As the incident rays of light reach the convex mirror, they reflect off the bulging out surface.
- The reflection takes place at this surface due to the curvature of the mirror.
- The reflection follows the law of reflection, where the angle of incidence is equal to the angle of reflection.

4. Diverging Nature:
- After reflection, the rays of light diverge or spread out.
- This is because the bulging out surface causes the reflected rays to spread in different directions.
- The reflected rays do not converge at a point like in a concave mirror.

5. Image Formation:
- Due to the diverging nature of the reflected rays, a virtual and diminished image is formed in a convex mirror.
- The image is formed behind the mirror, and it appears smaller than the actual object.

In conclusion, the reflection of light in a convex mirror takes place at the bulging out surface due to the curvature of the mirror. The bulging out surface causes the reflected rays to diverge, resulting in the formation of a virtual and diminished image.

Which one is a transparent object?
  • a)
    Dense fog
  • b)
    Wax paper
  • c)
    Stone
  • d)
    Reading glass
Correct answer is option 'D'. Can you explain this answer?

Pankaj Saini answered
Transparent objects allow light to pass through them, making objects behind them visible. They have the property of transmitting light without scattering it. Out of the given options, the transparent object is reading glass (option D).

Reasoning:
- Dense fog (option A): Fog consists of tiny water droplets or ice crystals suspended in the air. These particles scatter light, making it difficult to see through fog. Thus, it is not a transparent object.
- Wax paper (option B): Wax paper is a semi-transparent material. It allows some light to pass through, but it scatters and diffuses the light. Therefore, it is not completely transparent.
- Stone (option C): Stones are generally opaque. They do not allow light to pass through, and therefore, they are not transparent.
- Reading glass (option D): Reading glass, also known as a magnifying glass, is a transparent object. It is made of a convex lens that bends light and magnifies the object being viewed. When light passes through the lens, it is not scattered or absorbed significantly, allowing objects to be seen clearly. Reading glasses are commonly used to magnify small text or objects.

Key Points:
- Transparent objects allow light to pass through them without scattering it.
- Dense fog scatters light, making it difficult to see through.
- Wax paper is semi-transparent and scatters light.
- Stones are generally opaque and do not transmit light.
- Reading glass is a transparent object that allows light to pass through without significant scattering.

In conclusion, reading glass is the transparent object among the given options. It allows light to pass through without scattering, making objects behind it visible.

Light is
  • a)
    mass less
  • b)
    a transverse wave
  • c)
    a electromagnetic radiation
  • d)
    all of the above 
Correct answer is option 'D'. Can you explain this answer?

Meghana verma answered
Light is

  • massless

  • a transverse wave

  • an electromagnetic radiation

  • all of the above



Explanation:


Light is a form of energy that travels through space at a speed of 299,792,458 meters per second. It is made up of tiny particles called photons which have no mass. Therefore, light is considered as massless.


Light is a transverse wave which means that the vibrations of the wave are perpendicular to the direction of its propagation. The oscillations of the electric and magnetic fields in the wave generate the wave motion perpendicular to the direction of the fields. The oscillations of the fields are responsible for the light’s properties such as its intensity and polarization.


Light is also an electromagnetic radiation which means it consists of electric and magnetic fields that oscillate perpendicular to each other and propagate through space. These fields are created by the movement of charged particles. Electromagnetic radiation includes visible light, radio waves, microwaves, X-rays, and gamma rays.


Therefore, the correct answer is option 'D' - all of the above.

A source of light is
  • a)
    an object that can reflect light
  • b)
    an object that can refract light
  • c)
    an object that can absorb light
  • d)
    an object that can give light 
Correct answer is option 'D'. Can you explain this answer?

Veena kapoor answered
Introduction:
Light is a form of energy that enables us to see things around us. Without light, the world would be in complete darkness. Light can come from different sources, and in this question, we are asked to identify the source of light.

Explanation:
The correct answer is option 'D,' an object that can give light. Let's understand why.

Natural Sources of Light:
1. Sun: The sun is the primary source of light on earth. It emits light and heat that sustains life on our planet.
2. Stars: Other stars in the universe also emit light, and we can see them twinkling in the night sky.
3. Lightning: Lightning is another natural phenomenon that produces light.

Artificial Sources of Light:
1. Incandescent bulbs: Incandescent bulbs use a filament that heats up and emits light when an electric current passes through it.
2. Fluorescent lamps: Fluorescent lamps use gas and electricity to produce ultraviolet light, which then interacts with a phosphorescent coating to produce visible light.
3. LED lights: LED lights use a semiconductor material that emits light when an electric current passes through it.

Conclusion:
In conclusion, objects that can give light are the source of light. Natural sources of light like the sun, stars, and lightning, as well as artificial sources like incandescent bulbs, fluorescent lamps, and LED lights, are all examples of objects that can give light.

Which of the following statement is true?
  • a)
    A plane mirror sometimes form an inverted image.
  • b)
    A concave mirror always forms a virtual, erect and diminished image.
  • c)
    A concave lens always forms a virtual, erect and diminished image
  • d)
    None of these 
Correct answer is option 'C'. Can you explain this answer?

Ameya Kumar answered
A concave lens always forms a virtual, erect and diminished image.


Explanation:


A concave lens is a lens that is thinner at the center and thicker at the edges. It is also known as a diverging lens because it causes parallel light rays to spread out or diverge. When light rays pass through a concave lens, they refract or bend away from the normal, causing the rays to spread out.


Formation of Image by a Concave Lens:


1. Virtual Image:
When an object is placed in front of a concave lens, the light rays from the object diverge after passing through the lens. These diverging rays appear to come from a point behind the lens. Therefore, a concave lens always forms a virtual image, which means the image cannot be projected onto a screen.


2. Erect Image:
The image formed by a concave lens is always erect, meaning it is not inverted. This is because the light rays diverge after passing through the lens and do not intersect to form a real image.


3. Diminished Image:
A concave lens always forms a diminished image, which means the size of the image is smaller than the size of the object. The divergence of light rays causes the image to be smaller in size.


Contrast with Convex Lens:


A convex lens, on the other hand, is thicker at the center and thinner at the edges. It is also known as a converging lens because it causes parallel light rays to converge or come together. When light rays pass through a convex lens, they refract or bend towards the normal, causing the rays to converge.


A convex lens can form both real and virtual images, depending on the position of the object. Real images are formed when the object is placed beyond the focal point of the lens, while virtual images are formed when the object is placed between the lens and its focal point.


Therefore, the correct statement is that a concave lens always forms a virtual, erect, and diminished image.

At a particular time of a day, the ratio of height of an object and the length of it’s shadow is ‘x’. Using this calculate the height of a tree if the length of the shadow of tree is L.
  • a)
    x + L
  • b)
    x × L
  • c)
    L – x
  • d)
    x/L
Correct answer is option 'B'. Can you explain this answer?

Arshiya Pillai answered
During the same time the ratio of the height and length of any object will be equal to that of any other including ‘x’.
Step 1- Let the height of the tree be ‘h’. The length of the tree is given as ‘L’
∴ the ratio of its height and length would be h/L
Step 2- This ratio will be the same as ‘x’

Radius of curvature for a plane mirror is
  • a)
    positive
  • b)
    negative
  • c)
    infinity
  • d)
    none of these 
Correct answer is option 'C'. Can you explain this answer?

Yamini Singh answered
The correct answer is option 'C' - infinity.

A plane mirror is a flat, smooth surface that reflects light. It is called a "plane" mirror because its surface is perfectly flat and does not have any curvature or bending. Unlike curved mirrors such as concave and convex mirrors, a plane mirror does not have a radius of curvature.

Explanation:
1. Plane mirror characteristics:
- A plane mirror reflects light in a way that the angle of incidence (the angle at which light hits the mirror) is equal to the angle of reflection (the angle at which light reflects off the mirror).
- The image formed by a plane mirror is virtual, meaning that it cannot be projected onto a screen. It appears to be behind the mirror, but it cannot be physically touched or captured.
- The size of the image formed by a plane mirror is the same as the size of the object being reflected.

2. Curved mirrors and radius of curvature:
- Curved mirrors, such as concave and convex mirrors, have a curved surface that bends or curves inward or outward.
- The radius of curvature is the distance between the center of the mirror and its curved surface.
- For a concave mirror, the radius of curvature is positive because the mirror surface curves inward.
- For a convex mirror, the radius of curvature is negative because the mirror surface curves outward.

3. Plane mirror and radius of curvature:
- In contrast to curved mirrors, a plane mirror does not have a curved surface. Its surface is perfectly flat and smooth.
- As a result, a plane mirror does not have a radius of curvature.
- The absence of curvature in a plane mirror is what allows it to reflect light in a predictable and consistent manner, maintaining the same angle of incidence and reflection.

Therefore, the radius of curvature for a plane mirror is infinity because it does not have any curvature.

Sky appear red during
  • a)
    During noon
  • b)
    During early noon
  • c)
    Sunrise and sunset
  • d)
    During day
Correct answer is option 'C'. Can you explain this answer?

Gopal Kumar answered
Sky appears red during sunrise and sunset because rays of light travel longer distance during sun rise and sunset to scatter other colour light.

White light consist of
  • a)
    3 colours
  • b)
    7 colours
  • c)
    9 colours
  • d)
    5 colours
Correct answer is option 'B'. Can you explain this answer?

Siddharth Sharma answered
White light consists of 7 colours which can be visualised when white light passes through a prism.

Which of the following is luminous?
  • a)
    earth
  • b)
    coal
  • c)
    moon
  • d)
    bulb
Correct answer is option 'D'. Can you explain this answer?

Soumya Gupta answered
Objects that can emit light energy by themselves are known as luminous objects.
These objects can cause a sensation of light.
The luminous objects are visible as they emit light on their own.

Chapter doubts & questions for Light - Science Olympiad Class 7 2025 is part of Class 7 exam preparation. The chapters have been prepared according to the Class 7 exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Class 7 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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