Class 7 Science -Chapter 15- Light- Definition and Explanation of Important Keywords

Concave Lens

• Definition- A concave lens is a lens that curves inwards. It’s thinner in the middle and thicker at the edges.
• Explanation- When light passes through a concave lens, it spreads out or diverges. This type of lens makes things look smaller than they are. It’s used in things like peepholes on doors to give a wider view and in some types of glasses to correct vision.

Concave Mirror

• Definition- A concave mirror is a mirror that curves inward, like the inside of a spoon.
• Explanation- This mirror can make things look bigger when they are close to it. It’s used in devices where we need to see an enlarged image, like in satellite dishes to collect signals, in car headlights to focus light, and by dentists to see teeth more clearly.

Also Check – Convex Lenses- Principles, Applications, and Insights

Convex Lens

• Definition- A convex lens is thicker in the centre and thinner at the edges, curving outward.
• Explanation- This lens bends light rays inward and can make objects look larger. It’s used in magnifying glasses to make small things easier to see, and in cameras, telescopes, and binoculars to help focus and create clear images of distant objects.

Also Check – Difference Between a Convex and Concave Lens

Convex Mirror

• Definition- A convex mirror bulges outwards, like the back of a spoon.
• Explanation- It spreads out light rays, making the objects appear smaller but providing a wider view. This is why it’s used in car side mirrors to see a larger area behind the car and in stores for security, as it lets you see more of the store.

Also Check – Class 7 Science -Chapter 15 – Light- Complete Notes

Erect Image

• Definition- An erect image is an image that appears upright, just like the actual object.
• Explanation- This is the type of image you see in a normal mirror where the top of the object is at the top in the image, and the bottom is at the bottom. However, remember, in a plane mirror, the left and right sides are switched – this is called lateral inversion.

Also Check – Chapter 11- A Detailed Guide to the Light Activities for Class 7 Students

Magnified Image

• Definition- A magnified image is an image that appears larger than the actual object.
• Explanation- When you look at something through a lens or a mirror that makes it look bigger, you’re seeing a magnified image. This happens because the lens or mirror bends light in a way that stretches out the image, like when you look at yourself in the back of a spoon and your face looks bigger.

Magnifying Glass

• Definition- A magnifying glass is a tool that makes small things look bigger.
• Explanation- It’s a convex lens, which means it’s thicker in the middle and thinner at the edges. When you look through it, the lens bends the light in a way that enlarges the image of whatever you’re looking at, making it easier to see small details, like the words in a book or tiny insects.

Also Check – NCERT Solutions for Class 7 Science Chapter 15 -Light

Prism

• Definition- A prism is a solid glass object with flat, polished surfaces.
• Explanation- When light passes through a prism, it breaks up into different colours, like a rainbow. This happens because different colours of light bend by different amounts as they pass through the prism. It shows that white light is actually made up of many colours!

Rainbow

• Definition- A rainbow is a colourful arc that appears in the sky when the sun shines while it’s raining.
• Explanation- Rainbows happen because raindrops act like tiny prisms. When sunlight passes through the raindrops, it breaks up into different colours, creating a rainbow. Each colour bends at a slightly different angle, so we see them spread out in a beautiful arc.

Also Check – What is Light? An Easy-to-Understand Guide

Real Image

• Definition- A real image is a type of image that can be projected onto a screen or surface.
• Explanation- It’s formed when light rays coming from an object actually meet or converge after being reflected or refracted. For example, when you use a projector to show a movie on a screen, you’re looking at real images. These images can be upside down or smaller than the actual object.

Rear View Mirror

• Definition- A rear view mirror is a mirror in cars and other vehicles, used to see what’s happening behind the vehicle.
• Explanation- It’s usually mounted inside the car, above the middle of the windshield. Drivers use it to check the road behind them, like seeing if other cars are close or if it’s safe to change lanes. In most cars, this mirror is flat, giving a true image of what’s happening behind.

Side Mirror

• Definition- Side mirrors are mirrors on the outside of vehicles, one on each side.
• Explanation- They help the driver see areas to the sides and behind the vehicle that they can’t see with just the rear view mirror. Most side mirrors on cars are convex mirrors, which means they curve outward. This gives drivers a wider view, so it’s easier to spot other vehicles, but it makes things look smaller than they are.

Spherical Mirror

• Definition- A spherical mirror is a mirror that has a curved surface, like part of a sphere.
• Explanation- There are two types of spherical mirrors-
  • Concave Mirror- Curves inward, like the inside of a spoon. It can make things look bigger and is used in things like car headlights to focus light.
  • Convex Mirror- Bulges outward, like the back of a spoon. It gives a wider view but makes things look smaller. It’s used in car side mirrors.

Virtual Image

• Definition- A virtual image is a type of image that cannot be projected onto a screen.
• Explanation- This image is formed when light rays appear to come from a certain point, but they don’t actually meet there. For example, when you look in a flat mirror, you see a virtual image. The image looks like it’s behind the mirror, but you can’t project it onto a screen because the light rays aren’t really coming from behind the mirror.

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