📌 How to Use
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📘 Study MCQs
Q1. Why is a concave mirror used by dentists to examine teeth?
• It makes teeth look smaller.
• It provides a wider view.
• It produces a magnified image.
• It lights up the mouth.
Answer: It produces a magnified image.
A dentist places a small concave mirror near the tooth. When the tooth is within the focal length, the mirror forms a virtual, erect, and enlarged image, making details easier to see.
Q2. Why are convex mirrors used as rear-view mirrors in cars and scooters?
• They give a larger field of view.
• They give a magnified image of vehicles behind.
• They give real images.
• They are cheaper than plane mirrors.
Answer: They give a larger field of view.
Convex mirrors diverge light, allowing the driver to see a wider area of the traffic behind, helping to prevent accidents, even though the images appear smaller.
Q3. Why is a concave reflector used in a torch?
• To diverge the light from the bulb.
• To converge the light into a parallel beam.
• To make the light colorful.
• To reduce the brightness.
Answer: To converge the light into a parallel beam.
The bulb is placed at the focus of the concave mirror. Light rays from the bulb, after reflection, travel as a strong, parallel beam, illuminating a distant area.
Q4. Why do our feet look shorter when standing in clear water?
• Due to reflection of light.
• Due to dispersion of light.
• Due to refraction of light.
• Due to absorption of light.
Answer: Due to refraction of light.
Light from the feet bends (refracts) as it leaves water and enters air. To an observer, the feet appear to be at a different, shallower position, making them look shorter.
Q5. Why does a pencil appear bent when dipped obliquely in a glass of water?
• Due to reflection at the water surface.
• Due to refraction of light.
• Due to the pencil being soft.
• Due to total internal reflection.
Answer: Due to refraction of light.
Light from the part of the pencil in water refracts (bends) as it passes from water to air. This makes the pencil seem bent at the water-air interface.
Q6. Why are concave mirrors used in solar cookers?
• They diverge sunlight over a large area.
• They reflect all light away from the cooker.
• They converge sunlight to a point, producing heat.
• They are good for storing food.
Answer: They converge sunlight to a point, producing heat.
A large concave mirror concentrates (converges) parallel rays of sunlight to its focal point, creating a very hot spot where the cooking pot is placed.
Q7. Why is it difficult to catch a fish in water with a spear by aiming directly at it?
• The fish moves too fast.
• Light from the fish reflects away.
• Light from the fish refracts, making it appear at a different position.
• The water makes the spear blunt.
Answer: Light from the fish refracts, making it appear at a different position.
Due to refraction, the fish appears shallower than it actually is. To catch it, one must aim slightly below the seen image of the fish.
Q8. Why are reading glasses (for old age) usually convex lenses?
• They diverge light to help see distant objects.
• They converge light to help see nearby objects clearly.
• They make things look smaller.
• They are fashionable.
Answer: They converge light to help see nearby objects clearly.
In old age, the eye lens weakens, a condition called presbyopia. Convex lenses converge light rays before they enter the eye, helping to focus nearby objects on the retina.
Q9. Why are concave lenses used in spectacles for short-sighted people (myopia)?
• They converge light rays.
• They diverge light rays before they enter the eye.
• They magnify distant objects.
• They reduce glare.
Answer: They diverge light rays before they enter the eye.
In myopia, the eye focuses images in front of the retina. A concave (diverging) lens spreads out the light rays slightly, so the eye’s lens can focus them correctly on the retina.
Q10. Why do stars twinkle?
• They emit light in pulses.
• Due to refraction of starlight by Earth’s atmosphere.
• Due to reflection by clouds.
• Because they are very far away.
Answer: Due to refraction of starlight by Earth’s atmosphere.
Starlight refracts through layers of Earth’s moving atmosphere, which continuously changes the path of light, causing the apparent position and brightness to fluctuate (twinkle).
Q11. Why does the Sun appear flattened at sunrise and sunset?
• Due to scattering of blue light.
• Due to refraction of sunlight by Earth’s atmosphere.
• Due to reflection from oceans.
• The Sun is actually closer then.
Answer: Due to refraction of sunlight by Earth’s atmosphere.
The atmosphere refracts sunlight. At sunrise/sunset, light from the lower edge of the Sun bends more than from the upper edge, making the Sun’s shape appear flattened.
Q12. Why are convex mirrors used at blind turns on roads?
• They make vehicles look bigger.
• They provide a wider view of the other side of the turn.
• They light up the turn at night.
• They are more durable.
Answer: They provide a wider view of the other side of the turn.
A convex mirror’s diverging property allows drivers to see traffic coming from the hidden side of a blind turn, preventing collisions.
Q13. Why is a convex lens used in a simple camera?
• To diverge light onto the film/sensor.
• To converge light from an object to form a real image on the film/sensor.
• To make the object look bigger.
• To take colorful pictures.
Answer: To converge light from an object to form a real image on the film/sensor.
A convex lens focuses (converges) light rays from a distant object to form a real, inverted, and diminished image on the camera’s film or digital sensor.
Q14. Why does a pool of water appear shallower than it actually is?
• Water absorbs light.
• Light reflects off the bottom.
• Light refracts at the water-air interface.
• The bottom is always sloped.
Answer: Light refracts at the water-air interface.
Light rays from the bottom of the pool bend away from the normal as they leave water for air. Our brain assumes light travels straight, so we perceive the bottom to be closer.
Q15. Why are concave mirrors used in headlights of cars and searchlights?
• To spread light everywhere.
• To produce a parallel beam of high intensity.
• To make the light red.
• To focus light inside the vehicle.
Answer: To produce a parallel beam of high intensity.
The bulb is placed at the focus of the concave mirror. Reflected rays emerge as a powerful parallel beam, illuminating the road far ahead.
Q16. Why does a lemon in a glass of water appear bigger than its actual size?
• The glass magnifies it.
• Water reflects more light.
• Due to refraction of light and the curved glass acting like a convex lens.
• The lemon absorbs water and swells.
Answer: Due to refraction of light and the curved glass acting like a convex lens.
The cylindrical glass with water acts as a converging lens (convex). This refracts light, producing a magnified, virtual image of the lemon.
Q17. Why is it advised to use a concave mirror for shaving?
• It gives a diminished image.
• It gives an enlarged, erect image of the face when held close.
• It gives a real image.
• It does not fog up.
Answer: It gives an enlarged, erect image of the face when held close.
When the face is placed between the pole and focus of a concave mirror, it forms a virtual, erect, and magnified image, making shaving easier and more precise.
Q18. Why does a driver see a rainy road at night as a dark, rough surface instead of a mirror?
• Headlights are too dim.
• Due to diffuse reflection from the rough water surface.
• Due to total internal reflection.
• Water absorbs all light.
Answer: Due to diffuse reflection from the rough water surface.
A smooth water surface causes regular reflection (like a mirror), but a rainy road has a rough water surface. This causes diffuse reflection, scattering light in all directions and making it appear dark.
Q19. Why do diamonds sparkle?
• They emit their own light.
• They have a very high refractive index and are cut to cause multiple total internal reflections.
• They reflect all light like a mirror.
• They are very hard.
Answer: They have a very high refractive index and are cut to cause multiple total internal reflections.
Diamond’s high refractive index (2.42) and specific cuts allow light entering it to undergo total internal reflection multiple times before exiting, creating a sparkling effect.
Q20. Why is a magnifying glass (a convex lens) used to read small print?
• It makes the letters appear smaller and clearer.
• It makes the letters appear larger and clearer when placed close to the page.
• It increases the light on the page.
• It reduces glare.
Answer: It makes the letters appear larger and clearer when placed close to the page.
When the small print is placed within the focal length of a convex lens, a virtual, erect, and magnified image is formed, making it easier to read.
Q21. Why does a coin at the bottom of a bucket filled with water appear raised?
• The water pushes it up.
• Due to refraction of light.
• Due to reflection from the water surface.
• The coin is magnetic.
Answer: Due to refraction of light.
Light from the coin refracts as it leaves water. The rays bend away from the normal, making the coin appear to be at a shallower depth than it actually is.
Q22. Why are convex mirrors used in supermarkets and stores for security?
• They make people look taller.
• They allow one person to see a large area of the store.
• They make products look more attractive.
• They are decorative.
Answer: They allow one person to see a large area of the store.
The wide field of view provided by convex mirrors helps staff monitor aisles for customer assistance and prevent shoplifting.
Q23. Why does a stick partially immersed in water look broken at the water surface?
• The water dissolves the stick.
• Due to reflection of light.
• Due to refraction of light.
• The stick is actually broken.
Answer: Due to refraction of light.
Light from the immersed part refracts as it leaves water, bending at the surface. This makes the stick appear displaced, giving the illusion of being broken.
Q24. Why are concave mirrors not used as rear-view mirrors in vehicles?
• They are too expensive.
• They give a highly diminished view.
• They give an inverted image.
• They give a very narrowed field of view and may invert images.
Answer: They give a very narrowed field of view and may invert images.
Concave mirrors can provide a magnified view but have a narrow field of view and can form inverted images if the object is beyond the focus, making them unsafe for rear-view.
Q25. Why do advanced telescopes use large concave mirrors instead of lenses?
• Mirrors are cheaper.
• Mirrors do not suffer from chromatic aberration (color fringing).
• Mirrors are easier to clean.
• Mirrors can be made much larger and lighter than lenses.
Answer: Mirrors do not suffer from chromatic aberration (color fringing).
Large lenses are heavy, can sag, and cause chromatic aberration (splitting of colors). Concave mirrors reflect all colors equally, avoiding this, and can be supported from behind, allowing them to be made very large.
Q26. Why does a person with hypermetropia (far-sightedness) use convex lens spectacles?
• To diverge light for nearby objects.
• To converge light for nearby objects.
• To diverge light for distant objects.
• To converge light for distant objects.
Answer: To converge light for nearby objects.
In hypermetropia, the eye focuses images behind the retina for nearby objects. Convex lenses add convergence, helping to focus the image correctly on the retina for near vision.
Q27. Why does a glass slab placed over writing not magnify it, but a convex lens does?
• The glass slab has parallel surfaces, so light refracts but does not converge to a point.
• The glass slab is too thin.
• The writing is not bright enough.
• The convex lens is made of special glass.
Answer: The glass slab has parallel surfaces, so light refracts but does not converge to a point.
A glass slab causes lateral displacement of light but not convergence. A convex lens has curved surfaces that bend light rays to converge at a focal point, creating magnification.
Q28. Why do we sometimes see a mirage of water on a hot road?
• Due to reflection from puddles.
• Due to total internal reflection of light from the sky.
• Due to refraction only.
• Due to clouds.
Answer: Due to total internal reflection of light from the sky.
Air near the hot road is less dense (rarer) than cooler air above. Light from the sky undergoes total internal reflection in this layered air, making the sky appear as a reflection on the road, like water.
Q29. Why is the power of a doctor’s reading glasses expressed in positive dioptres?
• They are for fashion.
• They use convex lenses, which have positive power.
• They use concave lenses, which have positive power.
• All lenses have positive power.
Answer: They use convex lenses, which have positive power.
Reading glasses for presbyopia use converging convex lenses to aid near vision. The power of a converging lens is positive, measured in positive dioptres (+D).
Q30. Why do objects under water look closer and bigger when viewed from above?
• Water magnifies everything.
• Due to refraction and the fact that our brain interprets light as traveling in straight lines.
• Water makes objects swell.
• Due to reflection from the surface.
Answer: Due to refraction and the fact that our brain interprets light as traveling in straight lines.
Light from underwater objects bends away from the normal as it exits water. Our eyes project these rays back in straight lines, making the object appear closer and often larger than it is.
Q31. Why are side mirrors of cars labeled “Objects in mirror are closer than they appear”?
• Convex mirrors make objects look smaller, so they seem farther away.
• Concave mirrors are used.
• To warn drivers about speed.
• It’s a legal requirement with no reason.
Answer: Convex mirrors make objects look smaller, so they seem farther away.
Convex mirrors always produce diminished images. A vehicle behind appears smaller in the mirror, creating the illusion that it is farther away than it actually is, hence the safety warning.
Q32. Why does a rainbow appear as an arc?
• The Earth is round.
• Due to dispersion and internal reflection in raindrops.
• Clouds form an arc.
• The Sun is round.
Answer: Due to dispersion and internal reflection in raindrops.
Sunlight undergoes refraction, dispersion (splitting into colors), and total internal reflection inside spherical raindrops. We see light from raindrops at a specific angle (42°), forming a circular arc.
Q33. Why does a person’s legs look short when they are standing in a swimming pool?
• Water pressure compresses legs.
• Due to refraction at the water surface.
• Due to reflection from the pool walls.
• Legs are actually shorter in water.
Answer: Due to refraction at the water surface.
Light from the legs underwater refracts as it exits. The rays bend, making the legs appear to start from a point higher than the actual feet, so they look shorter.
Q34. Why is a concave mirror suitable for applying makeup?
• It gives a real image.
• It gives a magnified, erect image of the face when held close.
• It gives a wide view of the room.
• It provides extra light.
Answer: It gives a magnified, erect image of the face when held close.
Like for shaving, when the face is within the focal length of a concave mirror, the virtual, erect, and enlarged image helps in applying makeup precisely.
Q35. Why does a thick glass window sometimes make objects viewed through it look slightly shifted?
• The window is dirty.
• Due to refraction of light through the glass.
• Due to reflection from the window.
• The objects are actually moving.
Answer: Due to refraction of light through the glass.
Light bends when entering and leaving the glass. This causes lateral displacement, making the object appear slightly shifted from its actual position.
Q36. Why are concave mirrors used in satellite TV dishes?
• To diverge the weak TV signals.
• To converge the weak TV signals to the receiver at the focus.
• To protect the dish from rain.
• For a sleek design.
Answer: To converge the weak TV signals to the receiver at the focus.
Satellite dishes are concave reflectors. They collect and concentrate (converge) weak microwave signals from a satellite onto a receiver placed at the focal point.
Q37. Why does a drop of water on a printed page act as a magnifier?
• Water is sticky.
• The curved surface of the drop acts as a convex lens.
• Water reflects light onto the letters.
• The paper swells.
Answer: The curved surface of the drop acts as a convex lens.
A small water drop has a convex surface. It refracts light, converging rays to form a magnified, virtual image of the letters beneath it.
Q38. Why do spectacles for myopia have lenses with negative power?
• They are made of a special material.
• They use concave lenses, which have negative power.
• They are for reading.
• All spectacles have negative power.
Answer: They use concave lenses, which have negative power.
Concave (diverging) lenses are used to correct myopia. The focal length of a concave lens is negative, so its power (1/f) is also negative.
Q39. Why does the setting Sun appear red?
• It is cooler.
• Due to scattering of blue light and refraction of red light through a longer atmospheric path.
• The Sun changes color.
• Due to pollution.
Answer: Due to scattering of blue light and refraction of red light through a longer atmospheric path.
At sunset, sunlight travels through a thicker layer of atmosphere. Shorter wavelength blue light scatters away more, leaving the longer wavelength red light to reach our eyes.
Q40. Why is it easier to read a book under a lamp that has an opaque shade directing light downwards?
• It reduces glare by providing diffuse reflection from the page.
• It makes the room warmer.
• It concentrates light on the page, increasing illumination.
• Both A and C.
Answer: Both A and C.
The shade directs light onto the page, increasing brightness. The page provides diffuse reflection, scattering light evenly into our eyes and reducing harsh glare.
Q41. Why does a convex lens held away from a paper under the Sun can burn a hole in it?
• The lens reflects sunlight.
• The lens converges sunlight to a small, hot focal point.
• The lens is made of flammable material.
• The paper is special.
Answer: The lens converges sunlight to a small, hot focal point.
A convex lens focuses parallel rays of the Sun to its real focus. The concentrated solar energy at this small spot generates enough heat to burn the paper.
Q42. Why does a person wearing spectacles sometimes see a glaring circle of light around car headlights at night?
• The spectacles are dirty.
• Due to reflection and refraction from the curved lens surfaces.
• Headlights are too bright.
• It is an eye problem.
Answer: Due to reflection and refraction from the curved lens surfaces.
The curved surfaces of spectacle lenses can cause internal reflections and refraction of bright light sources, creating glare rings or halos, especially at night.
Q43. Why are overhead projectors and slide projectors equipped with convex lenses?
• To diverge the light from the slide.
• To converge light from the slide and form a real, enlarged image on the screen.
• To make the projector look professional.
• To hold the slide in place.
Answer: To converge light from the slide and form a real, enlarged image on the screen.
A convex lens system in a projector takes the light from a small slide (object) and focuses it to form a large, real, and inverted image on a distant screen.
Q44. Why does a white shirt look brighter than a black shirt under the same light?
• White shirt emits its own light.
• White shirt reflects most of the light falling on it, while a black shirt absorbs most of it.
• Black shirt reflects all colors.
• White shirt is thicker.
Answer: White shirt reflects most of the light falling on it, while a black shirt absorbs most of it.
A white surface is a good diffuse reflector, scattering light in all directions to our eyes. A black surface absorbs most of the incident light, reflecting very little, so it appears dark.
Q45. Why is a periscope in a submarine uses plane mirrors and not lenses?
• Lenses are too heavy.
• Mirrors provide a clearer, non-inverted view without chromatic aberration.
• Lenses would magnify the view too much.
• Water pressure would break lenses.
Answer: Mirrors provide a clearer, non-inverted view without chromatic aberration.
Plane mirrors simply reflect light without distorting the image or splitting colors. They are reliable for providing a direct view of the surface. Lenses could invert images and cause other aberrations.
Q46. Why does a fluorescent tube light seem to extend beyond its physical ends when viewed from certain angles?
• Due to refraction in the glass.
• Due to total internal reflection within the glass tube.
• The light is actually longer.
• It’s an optical illusion of the eye.
Answer: Due to total internal reflection within the glass tube.
Light emitted inside the glass tube can undergo total internal reflection, traveling along the tube walls. When it exits the curved ends, it appears to come from beyond the physical end of the tube.
Q47. Why is a peephole (door viewer) in a door made with a combination of lenses?
• To make it look fancy.
• To provide a wide-angle view of the outside while keeping the viewer hidden.
• To magnify the visitor’s face.
• To reduce light.
Answer: To provide a wide-angle view of the outside while keeping the viewer hidden.
A door peephole typically uses a concave lens on the outside (to capture a wide field of view) and a convex lens on the inside (to magnify the image for the viewer), allowing a small, safe view.
Q48. Why does a wet, black asphalt road look darker than a dry one?
• Water adds black color.
• Water fills the rough surface, reducing diffuse reflection and allowing more light to be absorbed.
• Water reflects light like a mirror.
• The road cools down.
Answer: Water fills the rough surface, reducing diffuse reflection and allowing more light to be absorbed.
A dry road has a rough surface causing diffuse reflection. Water fills the gaps, making the surface smoother. Less light is scattered back (specular reflection occurs at a specific angle), so more light is absorbed, making it look darker from most viewing angles.
Q49. Why is it hard to judge the distance of an oncoming car at night if it has only one headlight working?
• One light is too dim.
• Our brain uses the separation between two points (like eyes or headlights) to judge depth. One point provides less information.
• The working headlight is misaligned.
• It is not hard; it’s easy.
Answer: Our brain uses the separation between two points (like eyes or headlights) to judge depth. One point provides less information.
Binocular vision (using two eyes) helps judge distance. Similarly, seeing two separated headlights gives a cue for distance. With one light, this cue is lost, making distance estimation difficult.
Q50. Why does a convex lens used as a magnifying glass not work well if the object is too far from the lens?
• The lens gets dirty.
• The image becomes real and inverted, not a magnified virtual one.
• The lens power is too weak.
• Light is insufficient.
Answer: The image becomes real and inverted, not a magnified virtual one.
A convex lens produces a virtual, magnified image only when the object is within its focal length. If placed beyond the focus, it forms a real image which may be inverted and not useful for simple magnification.