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Practice Class 7 Science MCQs on virtual images, concave mirrors, convex mirrors, dispersion of light, plane mirrors, reflection and image formation with detailed explanations.
Do You Know
Q1. A virtual image is one that:
Correct Answer: Cannot be obtained on a screen
Detailed Explanation:
A virtual image is an image formed when light rays appear to meet at a point but do not actually intersect there. Since the rays do not physically meet, the image cannot be projected onto a screen. This is the main characteristic that distinguishes a virtual image from a real image.
Virtual images are commonly formed by plane mirrors and convex mirrors. When you look into a mirror at home, the image you see is virtual because it appears to be behind the mirror. However, if you place a screen behind the mirror, no image can be captured on it.
Virtual images are usually erect (upright) and may appear enlarged, diminished, or of the same size depending on the type of mirror or lens used. In contrast, real images are formed when light rays actually converge and can be obtained on a screen.
The concept of virtual images is important in understanding how mirrors and lenses work in daily life. Many optical devices such as rear-view mirrors, dressing mirrors, and magnifying glasses produce virtual images.
This topic is frequently asked in Class 7 Science examinations and forms the foundation for advanced optics studies.
Real-Life Examples:
- Your image in a bathroom mirror.
- Images formed by vehicle side mirrors.
- Images seen in a dressing mirror.
Important NCERT Points:
- Virtual images cannot be obtained on a screen.
- They are formed by apparent intersection of rays.
- Plane mirrors produce virtual images.
- Virtual images are generally erect.
Exam-Oriented Fact:
Every image formed by a plane mirror is virtual and erect.
Quick Revision Line:
A virtual image cannot be formed on a screen because light rays do not actually meet.
Q2. Which mirror is used by dentists to see an enlarged image of teeth?
Correct Answer: Concave Mirror
Detailed Explanation:
Dentists use concave mirrors because they can produce enlarged images of nearby objects. When an object is placed between the pole and focus of a concave mirror, the image formed is virtual, erect, and magnified. This allows dentists to observe small details of teeth and gums more clearly.
A concave mirror has a reflecting surface that curves inward. Due to its shape, it converges light rays toward a focal point. Depending on the position of the object, different types of images can be formed.
In dental clinics, patients’ teeth are placed close to the mirror. Under these conditions, the mirror produces a larger image, helping dentists detect cavities, cracks, plaque deposits, and other dental issues.
Concave mirrors are also used in shaving mirrors and makeup mirrors because they provide a magnified view of the face. Their ability to enlarge images makes them extremely useful in situations requiring detailed observation.
Understanding the applications of concave mirrors helps students connect scientific concepts with practical uses in everyday life.
Real-Life Examples:
- Dentists use concave mirrors to examine teeth.
- Shaving mirrors often use concave surfaces.
- Makeup mirrors provide enlarged facial images.
Important NCERT Points:
- Concave mirrors can form magnified images.
- They are also called converging mirrors.
- Image size depends on object position.
- Used where detailed viewing is required.
Exam-Oriented Fact:
A concave mirror forms a magnified image when the object is placed within its focal length.
Quick Revision Line:
Dentists use concave mirrors because they produce enlarged images of teeth.
Q3. The splitting of white light into its seven colors is called:
Correct Answer: Dispersion
Detailed Explanation:
Dispersion is the phenomenon in which white light splits into its constituent seven colors when it passes through a prism. These colors are Violet, Indigo, Blue, Green, Yellow, Orange, and Red, commonly remembered using the acronym VIBGYOR.
White light is actually a mixture of many colors. Each color has a different wavelength and bends by a different amount when passing through a transparent medium such as glass. Because of this difference in bending, the colors separate and become visible as a spectrum.
The most common natural example of dispersion is the formation of a rainbow. Tiny water droplets in the atmosphere act like miniature prisms and split sunlight into different colors.
The discovery of dispersion by Isaac Newton helped scientists understand the true nature of white light. His experiments showed that white light contains all visible colors.
Dispersion is important in optics and has applications in scientific instruments used for studying light and its properties.
Real-Life Examples:
- Formation of a rainbow after rain.
- Light passing through a glass prism.
- Color patterns seen in crystals.
Important NCERT Points:
- White light consists of seven colors.
- Dispersion occurs due to different refraction of colors.
- A prism can produce dispersion.
- Rainbow formation is an example of dispersion.
Exam-Oriented Fact:
The sequence of colors in dispersion is VIBGYOR.
Quick Revision Line:
Dispersion is the splitting of white light into seven colors.
Q4. Convex mirrors are used as side-view mirrors in vehicles because:
Correct Answer: They can form images of objects spread over a large area
Detailed Explanation:
Convex mirrors are commonly used as side-view mirrors in cars, buses, and motorcycles because they provide a wider field of view. Their outward-curved reflecting surface allows drivers to see a larger area behind and beside the vehicle.
A convex mirror always forms a virtual, erect, and diminished image regardless of the object’s position. Although the image appears smaller, a greater portion of the surroundings becomes visible.
This wider view helps drivers monitor traffic more effectively and reduces blind spots. Because of this safety advantage, convex mirrors are preferred for rear-view and side-view applications.
The words “Objects in mirror are closer than they appear” are often printed on vehicle mirrors because convex mirrors make objects appear smaller and therefore seem farther away than they actually are.
Convex mirrors are also used in shops, parking lots, hospitals, and security systems where a broad viewing area is needed.
Real-Life Examples:
- Side mirrors of cars and motorcycles.
- Security mirrors in shopping malls.
- Mirrors at road intersections.
Important NCERT Points:
- Convex mirrors provide a wide field of view.
- They always form virtual images.
- Images are erect and diminished.
- Used for safety purposes.
Exam-Oriented Fact:
Convex mirrors help drivers see a larger area behind their vehicles.
Quick Revision Line:
Convex mirrors are used in vehicles because they show a wider area of surroundings.
Q5. An object is placed at 5 cm in front of a plane mirror. The distance between the object and its image will be:
Correct Answer: 10 cm
Detailed Explanation:
A plane mirror forms an image at the same distance behind the mirror as the object is placed in front of it. This is one of the fundamental properties of image formation by plane mirrors.
If an object is placed 5 cm in front of a plane mirror, the image will be formed 5 cm behind the mirror. Therefore, the total distance between the object and its image will be:
Thus, the distance between the object and the image is 10 cm.
Plane mirrors always form virtual, erect images of the same size as the object. The image is laterally inverted, meaning the left and right sides appear reversed.
This property of equal object and image distance is widely used in optical calculations and is frequently asked in school examinations. Understanding this concept helps students solve mirror-related numerical problems easily.
Plane mirrors are among the simplest optical devices and are commonly found in homes, schools, laboratories, and vehicles.
Real-Life Examples:
- Images seen in dressing mirrors.
- Bathroom mirrors.
- Mirror reflections in daily life.
Important NCERT Points:
- Object distance equals image distance.
- Plane mirrors form virtual and erect images.
- Image size equals object size.
- Images are laterally inverted.
Exam-Oriented Fact:
In a plane mirror, image distance is always equal to object distance.
Quick Revision Line:
If an object is 5 cm from a plane mirror, its image forms 5 cm behind the mirror, making the total distance 10 cm.
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