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Q1. When two plane mirrors are placed at an angle to each other, the number of images formed is given by the formula:
The number of images formed by two plane mirrors placed at an angle is given by the formula n = (360/θ) − 1, where θ is the angle between the mirrors. This formula works when 360/θ is a whole number. For example, if the angle is 60°, then n = (360/60) − 1 = 6 − 1 = 5 images. The other formulas are incorrect. The ‘− 1’ is used because one image is lost when counting reflections.
Q2. If two plane mirrors are placed at 60° to each other, how many images will be formed?
The number of images formed by two plane mirrors placed at 60° is calculated as n = (360/60) − 1 = 6 − 1 = 5 images. This is a direct application of the formula n = (360/θ) − 1. The angle is 60°, so the number of images is 5. The other options are incorrect.
Q3. If two plane mirrors are placed parallel to each other (angle = 0°), the number of images formed is:
When two plane mirrors are placed parallel to each other, the angle between them is 0°. The formula n = (360/0) − 1 is undefined, meaning an infinite number of images are formed. Each reflection between the mirrors creates a new image, and the process continues indefinitely, creating a long series of images that fade in intensity. Thus, the number of images is infinite.
Q4. A kaleidoscope uses which of the following to create beautiful patterns?
A kaleidoscope uses two or three plane mirrors arranged in a tube to create multiple reflections of coloured objects placed at one end. The multiple reflections create beautiful symmetrical patterns. It does not use one mirror, a concave mirror, or a convex lens. The patterns are formed due to multiple reflections.
Q5. The patterns in a kaleidoscope change when:
When the tube of a kaleidoscope is rotated, the coloured objects at the end shift position, and the multiple reflections create new, changing patterns. The colour of the tube, its length, or the outer covering do not affect the patterns. Rotation is what creates the changing symmetrical designs.
Q6. Sunlight appears white to us because:
Sunlight appears white because it is composed of all seven colours of the visible spectrum: violet, indigo, blue, green, yellow, orange, and red. When these colours are mixed together, they appear white to our eyes. It is not just white, colourless, or reflected from the moon.
Q7. The splitting of white light into its seven colours is called:
Dispersion is the phenomenon of splitting white light into its constituent seven colours. This happens when light passes through a prism. Reflection is the bouncing back of light, refraction is the bending of light, and absorption is when light is taken in by a material. Dispersion is the correct term for splitting light into colours.
Q8. The part of the eye that controls the amount of light entering the eye is called:
The iris is the coloured part of the eye that controls the amount of light entering the eye by adjusting the size of the pupil. In bright light, the iris makes the pupil smaller, and in dim light, it makes the pupil larger. The retina is the light-sensitive layer, the cornea is the transparent front part, and the lens focuses light.
Q9. The black hole in the centre of the iris is called:
The pupil is the black hole in the centre of the iris. It is the opening through which light enters the eye. The size of the pupil is controlled by the iris. The cornea is the transparent front part, the retina is the back layer, and the lens focuses light.
Q10. The transparent front part of the eye that covers the iris and pupil is called:
The cornea is the transparent, curved front part of the eye that covers the iris and pupil. It helps focus light entering the eye. The sclera is the white outer layer, the retina is the light-sensitive layer, and the optic nerve carries signals to the brain.
Q11. The lens inside the eye is:
The lens inside the eye is soft and flexible. It changes shape to focus light on the retina for near or distant objects. This ability is called accommodation. It is not hard, made of metal, or opaque. Its flexibility allows us to see objects at different distances.
Q12. The layer at the back of the eyeball that is sensitive to light is called:
The retina is the light-sensitive layer at the back of the eyeball. It contains rod and cone cells that detect light and colour. The cornea is the front transparent layer, the iris controls light entry, and the sclera is the white outer protective layer.
Q13. The cells in the retina that are sensitive to dim light but do not detect colour are called:
Rods are the light-sensitive cells in the retina that are sensitive to dim light and do not detect colour. They are responsible for vision in low light conditions and for peripheral vision. Cones are sensitive to bright light and detect colour. Lens and cornea cells are not in the retina.
Q14. The cells in the retina that are sensitive to bright light and detect colour are called:
Cones are the light-sensitive cells in the retina that are sensitive to bright light and are responsible for colour vision and sharpness. Rods are sensitive to dim light and do not detect colour. Iris cells and optic cells are not part of the retina’s light-detecting system.
Q15. The nerve that carries signals from the retina to the brain is called:
The optic nerve carries signals from the retina to the brain, where they are interpreted as images. The auditory nerve carries sound signals, sensory nerves carry general sensations, and motor nerves control muscles. The optic nerve is specifically for vision.
Q16. Which of the following is a correct way to care for your eyes?
Washing eyes with clean, cold water regularly is a good practice for eye care. Reading in dim light, rubbing eyes with dirty hands, and staring at the sun are harmful and can damage the eyes. Washing eyes helps keep them clean and refreshed.
Q17. To protect eyes from computer or mobile screen strain, one should:
To reduce eye strain from screens, one should follow the 20-20-20 rule: take a break every 20 minutes and look at a distant object for at least 20 seconds. Sitting close, using screens in darkness, and not blinking are harmful. This practice gives the eyes rest.
Q18. If dust or a small particle enters the eye, you should:
If dust or a small particle enters the eye, the correct action is to wash the eye with clean water or use an eye wash. Rubbing the eye can cause scratches, ignoring it can lead to infection, and using random eye drops is unsafe. Washing is the safest method.
Q19. The Braille system is used by:
The Braille system is used by visually impaired (blind) people to read and write. It uses raised dots that are read by touch. Deaf people use sign language, people who cannot speak use other communication methods, and memory loss is unrelated.
Q20. In the Braille system, a cell consists of how many dots?
In the Braille system, a cell consists of 6 dots arranged in 2 columns of 3 dots each (a 2×3 grid). Each letter or symbol is represented by a different pattern of raised dots. This is the standard Braille cell. It is not 4, 8, or 10 dots.
Q21. Braille was invented by:
The Braille system was invented by Louis Braille, a Frenchman who was blind himself. Alexander Graham Bell invented the telephone, Helen Keller was a famous advocate for the blind, and Isaac Newton was a physicist. Louis Braille is the correct answer.
Q22. Lateral inversion means:
Lateral inversion means the left-right reversal of an image in a plane mirror. The image is not inverted top-bottom; it is only left-right swapped. The image is the same size as the object, not larger or smaller. This is a key characteristic of plane mirror images.
Q23. The word AMBULANCE is written in reverse on the front of an ambulance so that:
The word AMBULANCE is written in reverse on the front of an ambulance so that when a driver sees it in their rear-view mirror, it appears normal and readable. This helps drivers quickly identify the ambulance. It is not for distance, paint saving, or artistic purposes.
Q24. The image formed by a plane mirror is laterally inverted. This means the image is:
Lateral inversion in a plane mirror means the image is inverted left to right. The top and bottom remain the same. The image is not inverted front to back, and it is inverted in terms of left-right orientation. This is a key property of plane mirror images.
Q25. Which part of the eye acts like a screen on which the image is formed?
The retina acts like a screen on which the image is formed. Light entering the eye is focused by the cornea and lens onto the retina, where rod and cone cells detect the image. The cornea and lens focus light, and the iris controls light entry. The retina is the sensitive layer.
Q26. Rods are more sensitive to light than cones. This is why:
Rods are more sensitive to light but do not detect colour. In very dim light, rods are active and cones are not, so we see only in shades of black and white. This is why colours are not visible in dim light. Our pupils become larger, not smaller, in dim light.
Q27. The number of images formed when two plane mirrors are placed at 90° to each other is:
The number of images formed by two plane mirrors at 90° is n = (360/90) − 1 = 4 − 1 = 3 images. This is a direct application of the formula. Two mirrors at 90° give three images. The other options are incorrect.
Q28. A kaleidoscope is based on the principle of:
A kaleidoscope is based on the principle of multiple reflections of light. Mirrors placed inside the tube create many reflected images of coloured objects, forming symmetrical patterns. Refraction, dispersion, and absorption are not the principles behind a kaleidoscope.
Q29. Sunlight is composed of seven colours. This can be demonstrated using:
A glass prism can demonstrate that sunlight is composed of seven colours by dispersing white light into its constituent colours. A plane mirror reflects light, a convex lens focuses light, and a kaleidoscope creates multiple reflections. The prism is the instrument used for dispersion.
Q30. The coloured part of the eye that gives the eye its colour (blue, brown, green) is called:
The iris is the coloured part of the eye that gives it its colour (blue, brown, green, etc.). The retina is the light-sensitive layer, the cornea is the transparent front part, and the pupil is the black hole in the centre. The iris controls the amount of light entering the eye.
Q31. To keep eyes healthy, one should eat foods rich in:
Vitamin A is essential for good vision and eye health. It helps maintain the retina and prevents night blindness. Foods like carrots, spinach, and sweet potatoes are rich in Vitamin A. Vitamin C, D, and B12 are important for other functions, but Vitamin A is specifically crucial for eyes.
Q32. The minimum distance for reading a book without straining the eyes is about:
The minimum distance for reading a book without straining the eyes is about 25 cm. This is the near point of the eye for a normal person. Reading closer than 25 cm can cause eye strain and fatigue. The other distances are not optimal for reading.
Q33. Which of the following is NOT a good practice for eye care?
Watching television in a completely dark room is not a good practice for eye care because the contrast between the bright screen and the dark room can strain the eyes. Reading in a well-lit room, taking breaks, and regular check-ups are all good practices.
Q34. In the Braille system, raised dots are read by:
In the Braille system, raised dots are read by fingers through touch. Blind individuals use their fingertips to feel the patterns of raised dots. Eyes are not used because the system is for visually impaired people. Ears and nose are not used for reading Braille.
Q35. The white outer layer of the eyeball that protects it is called:
The sclera is the white, tough outer layer of the eyeball that protects it and gives it its shape. The cornea is the transparent front part, the retina is the light-sensitive layer, and the choroid is a vascular layer. The sclera is the protective white layer.
Q36. The fluid that fills the space between the cornea and the lens is called:
The aqueous humour is the clear fluid that fills the space between the cornea and the lens. It helps maintain the shape of the eye and provides nutrients. The vitreous humour fills the main cavity behind the lens. Blood and tears are not the fluids in this space.
Q37. The jelly-like substance that fills the main cavity of the eyeball behind the lens is called:
The vitreous humour is the clear, jelly-like substance that fills the main cavity of the eyeball behind the lens. It helps maintain the shape of the eye. The aqueous humour is in front of the lens, and lens fluid and retinal fluid are not standard terms.
Q38. When you see your face in a plane mirror, your left ear appears as the right ear in the image. This is due to:
Lateral inversion causes your left ear to appear as the right ear in a plane mirror image. This is the left-right reversal characteristic of plane mirrors. Dispersion splits light, refraction bends light, and diffuse reflection scatters light. Lateral inversion is the correct term.
Q39. If you hold a sign with the word LEFT in front of a plane mirror, what will the mirror show?
The mirror will show the word TFEL because of lateral inversion. The letters are reversed left-to-right. The first letter (L) appears as the last letter (L), the second (E) as the second last (E), the third (F) as the third (F), and the last (T) as the first (T). So LEFT becomes TFEL. The word does not remain the same.
Q40. The retina contains approximately how many rod cells?
The retina contains approximately 120 million rod cells, which are sensitive to dim light. Cone cells are about 6 million. The rods are responsible for peripheral and night vision. 1 million is too low, and 10 billion is too high.
Q41. Cones in the retina are responsible for:
Cones in the retina are responsible for colour vision and sharpness (visual acuity). They work best in bright light. Rods are responsible for night vision and peripheral vision. Cones detect colours and fine details.
Q42. If a person cannot see colours, it is usually due to a defect in:
Colour blindness is usually due to a defect in the cones, which are responsible for colour vision. Rods are not involved in colour detection. The lens and cornea focus light but do not detect colour. A defect in cones leads to difficulty in distinguishing colours.
Q43. In a kaleidoscope, the number of mirrors used is typically:
A kaleidoscope typically uses two or three plane mirrors arranged in a tube. The mirrors are placed at an angle to create multiple reflections and symmetrical patterns. One mirror would not create multiple images, and four or five mirrors are not standard in a simple kaleidoscope.
Q44. When two plane mirrors are placed at 45° to each other, the number of images formed is:
The number of images formed by two plane mirrors at 45° is n = (360/45) − 1 = 8 − 1 = 7 images. This is a direct application of the formula. The angle is 45°, so the number of images is 7. The other options are incorrect.
Q45. The part of the eye that changes shape to focus on near or distant objects is the:
The lens changes shape to focus on near or distant objects, a process called accommodation. The cornea also helps focus light but does not change shape. The iris controls light entry, and the retina detects light. The lens is flexible and adjusts its curvature.
Q46. Braille symbols are created by:
Braille symbols are created by raising dots on paper in specific patterns. These raised dots are read by touch. Cutting holes, printing coloured ink, or drawing lines are not part of the Braille system. The dots are raised so that blind individuals can feel them.
Q47. Which of the following statements about lateral inversion is true?
Lateral inversion is a characteristic of plane mirrors only. In curved mirrors (concave or convex), the image may be inverted or upright but does not show lateral inversion in the same way. Lateral inversion is specific to plane mirrors.
Q48. To avoid eye strain while reading, the light should come from:
To avoid eye strain while reading, the light should come from behind you and fall on the book. This provides good illumination without shining directly into your eyes. Light shining into your eyes causes glare and strain. The other positions are not ideal for comfortable reading.
Q49. The phenomenon of multiple images is used in:
Multiple images are used in a kaleidoscope (to create patterns) and a periscope (to see over obstacles). A simple microscope uses a convex lens, a glass prism disperses light, and a convex lens focuses light. Multiple reflections are the principle behind kaleidoscopes and periscopes.
Q50. The blind spot in the eye has no rods or cones because:
The blind spot has no rods or cones because it is the area where the optic nerve leaves the eye. There are no light-sensitive cells at this point, so no image is detected there. The iris, lens, and cornea are not locations of the blind spot. The blind spot is on the retina where the optic nerve exits.