SCIENCE QUIZ – ANSWER EXPLANATIONS
Q1. Where is the image formed when an object is at infinity in front of a concave mirror?
Correct Answer: At the focus F
- Why correct: According to Table 1.1, when the object is at infinity, the image is formed at the focus F.
- Why others wrong:
- “At the center of curvature C” is for objects placed at C
- “Between F and C” is for objects beyond C
- “Behind the mirror” is for objects between P and F
Q2. What is the nature of the image formed when an object is placed beyond C in front of a concave mirror?
Correct Answer: Real and inverted
- Why correct: Table 1.1 clearly states that for objects beyond C, the image is real and inverted.
- Why others wrong:
- “Virtual and erect” is for objects between P and F
- “Virtual and inverted” doesn’t occur with concave mirrors
- “Real and erect” contradicts the inversion property of real images
Q3. Where is the image formed when an object is placed at C in front of a concave mirror?
Correct Answer: At C
- Why correct: Table 1.1 specifies that when object is at C, image is also formed at C.
- Why others wrong:
- “At F” is for objects at infinity
- “Between F and C” is for objects beyond C
- “Beyond C” is for objects between C and F
Q4. What is the size of the image when an object is placed at C in front of a concave mirror?
Correct Answer: Same size
- Why correct: Table 1.1 indicates the image has the same size as the object when placed at C.
- Why others wrong:
- “Highly diminished” is for objects at infinity
- “Diminished” is for objects beyond C
- “Enlarged” is for objects between C and F
Q5. Where is the image formed when an object is placed between C and F in front of a concave mirror?
Correct Answer: Beyond C
- Why correct: Table 1.1 shows that for objects between C and F, the image is formed beyond C.
- Why others wrong:
- “At F” is for objects at infinity
- “At C” is for objects at C
- “Between F and C” is for objects beyond C
Q6. What is the size of the image when an object is placed between C and F in front of a concave mirror?
Correct Answer: Enlarged
- Why correct: Table 1.1 states the image is enlarged when object is between C and F.
- Why others wrong:
- “Highly diminished” is for objects at infinity
- “Diminished” is for objects beyond C
- “Same size” is for objects at C
Q7. Where is the image formed when an object is placed at F in front of a concave mirror?
Correct Answer: At infinity
- Why correct: Table 1.1 specifies that when object is at F, image is formed at infinity.
- Why others wrong:
- “At F” is for objects at infinity
- “At C” is for objects at C
- “Behind the mirror” is for objects between P and F
Q8. What is the size of the image when an object is placed at F in front of a concave mirror?
Correct Answer: Highly enlarged
- Why correct: Table 1.1 describes the image as highly enlarged when object is at F.
- Why others wrong:
- “Highly diminished” is for objects at infinity
- “Diminished” is for objects beyond C
- “Same size” is for objects at C
Q9. Where is the image formed when an object is placed between P and F in front of a concave mirror?
Correct Answer: Behind the mirror
- Why correct: Table 1.1 indicates that for objects between P and F, the image is formed behind the mirror.
- Why others wrong:
- “At F” is for objects at infinity
- “At C” is for objects at C
- “Beyond C” is for objects between C and F
Q10. What is the nature of the image formed when an object is placed between P and F in front of a concave mirror?
Correct Answer: Virtual and erect
- Why correct: Table 1.1 clearly states the image is virtual and erect for objects between P and F.
- Why others wrong:
- “Real and inverted” applies to all other positions except between P and F
- “Real and erect” contradicts the properties of real images in concave mirrors
- “Virtual and inverted” doesn’t occur with concave mirrors
Q11. What is the size of the image when an object is placed between P and F in front of a concave mirror?
Correct Answer: Enlarged
- Why correct: Table 1.1 specifies the image is enlarged when object is between P and F.
- Why others wrong:
- “Highly diminished” is for objects at infinity
- “Diminished” is for objects beyond C
- “Same size” is for objects at C
Q12. Which ray, after reflection from a concave mirror, passes through the principal focus?
Correct Answer: A ray parallel to the principal axis
- Why correct: Section 1.2.2 states that a ray parallel to principal axis passes through principal focus after reflection.
- Why others wrong:
- “A ray passing through the principal focus” emerges parallel to principal axis
- “A ray passing through the center of curvature” reflects back along same path
- “A ray incident obliquely to the principal axis” follows laws of reflection
Q13. Which ray, after reflection from a concave mirror, emerges parallel to the principal axis?
Correct Answer: A ray passing through the principal focus
- Why correct: Section 1.2.2 explains that a ray passing through principal focus emerges parallel to principal axis.
- Why others wrong:
- “A ray parallel to the principal axis” passes through principal focus
- “A ray passing through the center of curvature” reflects back along same path
- “A ray incident obliquely to the principal axis” follows laws of reflection
Q14. Which ray, after reflection from a concave mirror, is reflected back along the same path?
Correct Answer: A ray passing through the center of curvature
- Why correct: Section 1.2.2 states that a ray passing through center of curvature reflects back along same path.
- Why others wrong:
- “A ray passing through the principal focus” emerges parallel to principal axis
- “A ray parallel to the principal axis” passes through principal focus
- “A ray incident obliquely to the principal axis” follows laws of reflection
Q15. At the point of incidence on a spherical mirror, what relationship exists between the angle of incidence and angle of reflection?
Correct Answer: Angle of incidence equals angle of reflection
- Why correct: The text explicitly states “the laws of reflection are followed” and “angle of reflection equals the angle of incidence.”
- Why others wrong:
- “Angle of incidence is greater than angle of reflection” violates law of reflection
- “Angle of incidence is less than angle of reflection” violates law of reflection
- “They are complementary angles” is not mentioned in the context
Q16. For which position of the object in front of a concave mirror is the image highly diminished?
Correct Answer: At infinity
- Why correct: Table 1.1 describes the image as “highly diminished” when object is at infinity.
- Why others wrong:
- “Beyond C” produces diminished image (not highly diminished)
- “At C” produces same size image
- “Between C and F” produces enlarged image
Q17. For which position of the object in front of a concave mirror is the image diminished?
Correct Answer: Beyond C
- Why correct: Table 1.1 states the image is diminished when object is beyond C.
- Why others wrong:
- “At infinity” produces highly diminished image
- “At C” produces same size image
- “Between C and F” produces enlarged image
Q18. For which position of the object in front of a concave mirror is the image of the same size as the object?
Correct Answer: At C
- Why correct: Table 1.1 specifies “same size” when object is at C.
- Why others wrong:
- “At infinity” produces highly diminished image
- “Beyond C” produces diminished image
- “Between C and F” produces enlarged image
Q19. For which position of the object in front of a concave mirror is a virtual image formed?
Correct Answer: Between P and F
- Why correct: Table 1.1 shows virtual image is formed only when object is between P and F.
- Why others wrong:
- “Beyond C” produces real image
- “At C” produces real image
- “Between C and F” produces real image
Q20. What type of image is formed by a concave mirror when the object is placed between P and F?
Correct Answer: Virtual and erect
- Why correct: Table 1.1 clearly states “virtual and erect” for objects between P and F.
- Why others wrong:
- “Real and inverted” applies to all other positions
- “Real and erect” contradicts properties of concave mirrors
- “Virtual and inverted” doesn’t occur with concave mirrors
Q21. How can the approximate focal length of a concave mirror be determined?
Correct Answer: By obtaining the image of a distant object on a sheet of paper
- Why correct: Activity 1.3 describes this method: obtaining image of distant object to find focal length.
- Why others wrong:
- “By measuring the distance between P and C” gives radius, not focal length directly
- “By measuring the height of the mirror” is irrelevant to focal length
- “By calculating the radius of the mirror” requires additional measurements
Q22. In the activity with a concave mirror, when might you not get an image on the screen?
Correct Answer: When the object is between P and F
- Why correct: The text states “in one of the cases, you may not get the image on the screen” referring to when virtual image forms behind mirror.
- Why others wrong:
- Other positions all produce real images that can be captured on screen
- Virtual images cannot be obtained on screen
Q23. For a spherical mirror of small aperture, where does the principal focus F lie?
Correct Answer: Midway between P and C
- Why correct: The text explicitly states “the principal focus F lies midway between the pole P and the centre of curvature C.”
- Why others wrong:
- “At the pole P” is incorrect – P is the mirror surface point
- “At the center of curvature C” is incorrect – C is center of spherical surface
- “Beyond C” is incorrect – F is always between P and C
Q24. In ray diagrams for spherical mirrors, how many rays are typically considered for clarity?
Correct Answer: Two
- Why correct: Section 1.2.2 states “it is more convenient to consider only two rays, for the sake of clarity.”
- Why others wrong:
- “One” ray is insufficient to locate image point
- “Three” or “Four” are mentioned as possible but not typically used for clarity
Q25. What does the intersection of at least two reflected rays give in a ray diagram?
Correct Answer: The position of the point object image
- Why correct: The text states “the intersection of at least two reflected rays give the position of the point object.”
- Why others wrong:
- “The position of the pole” is fixed at mirror surface
- “The position of the focus” is predetermined by mirror geometry
- “The center of curvature” is fixed for a given mirror
Q26. A ray incident obliquely to the principal axis towards the pole of a concave mirror is reflected:
Correct Answer: Obliquely, following the laws of reflection
- Why correct: Section 1.2.2 explains such rays follow laws of reflection at point of incidence.
- Why others wrong:
- Other options describe specific ray paths that don’t apply to oblique incidence at pole
Q27. Which of the following statements about image formation by concave mirrors is correct?
Correct Answer: Images can be real or virtual depending on object position
- Why correct: The text explains images are real for some positions and virtual for others (between P and F).
- Why others wrong:
- “Images are always real” is false due to virtual images between P and F
- “Images are always virtual” is false – most positions produce real images
- “Images are always erect” is false – real images are inverted
Q28. When using a concave mirror, a sharp bright spot of light obtained on paper is actually:
Correct Answer: The image of the Sun
- Why correct: Activity 1.2 describes this as “the image of the Sun” forming a bright spot.
- Why others wrong:
- Other options don’t accurately describe the phenomenon observed
Q29. In the activity with the concave mirror and candle, where should the candle be placed to get a highly enlarged image?
Correct Answer: At F
- Why correct: Table 1.1 specifies “highly enlarged” image when object is at F.
- Why others wrong:
- “At C” produces same size image
- “Between C and F” produces enlarged image (not highly enlarged)
- “Between P and F” produces enlarged virtual image
Q30. What is the nature of the image formed by a concave mirror when the object is at the focus?
Correct Answer: Highly enlarged real and inverted
- Why correct: Table 1.1 describes the image as “highly enlarged” and “real and inverted” when object is at F.
- Why others wrong:
- “Real and inverted” is correct but incomplete (misses “highly enlarged”)
- “Virtual and erect” applies to objects between P and F
- “Real and erect” doesn’t occur with concave mirrors