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Q1. c. 2.25 × 10⁸ m/sQ2. c. YellowQ3. b. 6 m (Explanation: The distance of the object from the mirror is 3 m, and the distance of the image from the mirror is also 3 m. Therefore, the total distance between the object and its image is 3 m + 3 m = 6 m).Q4. b. A sheet of cardboard (Explanation: Cardboard has a rough surface which causes diffused reflection, whereas mirrors, wet roads, and polished surfaces lead to specular reflection).
Q5. lateral inversionQ6. refractive indexQ7. periscopeQ8. blue
Q9. False (Explanation: Diffused reflection is not a failure of the laws of reflection. The light rays reflect at different angles due to the irregularities of the surface, but each individual ray still obeys the laws of reflection).Q10. TrueQ11. False (Explanation: The angle of incidence is the angle between the incident ray and the normal).Q12. True
Q13. Term Explanations:a. Incident ray: The ray of light which strikes the reflecting surface.b. Normal: A perpendicular line drawn to the reflecting surface at the point of incidence.c. Colour subtraction: The process of determining the colour of an object when a beam of light of a single colour or a mixture of colours is thrown on it.Q14. Differences:a. Specular vs. Diffused Reflection: Specular reflection occurs when parallel rays of light fall on a smooth and polished surface (like a mirror) and the reflected rays remain parallel. Diffused reflection occurs when parallel rays of light strike a rough surface (like cardboard or paper) and reflect at different angles in different directions.b. Primary vs. Secondary Colours: Primary colours of light (Red, Green, and Blue) cannot be obtained by mixing any other colours of light. Secondary colours of light (Magenta, Cyan, and Yellow) are composite colours produced by mixing any two primary colours of light.
Q15. The three characteristics of the image formed by a plane mirror are:The size of the image is the same as the size of the object.The image formed is laterally inverted.The distance between the image and the mirror is the same as the distance between the object and the mirror.Q16. The word is written in a laterally inverted form so that drivers" in vehicles ahead of the ambulance can read the word the right way around (“AMBULANCE”) when looking at it through their rear-view mirrors".Q17. Calculations:a. Angle of incidence (∠i): The normal is perpendicular (90°) to the mirror surface. Since the ray makes an angle of 48° with the surface, the angle of incidence is:
b. Angle of reflection (∠r): According to the second law of reflection, the angle of reflection is equal to the angle of incidence:
Q18. A blue object absorbs all the colours of white light except blue, reflecting the blue light back to our eyes. If only red light is thrown on a blue object, it will appear black because there is no blue light to reflect, and the red light will be completely absorbed by the object.Q19. Diagram-Based Answer:
(Students should draw a diagram resembling Fig 4.2 in the text).Labels to include:Horizontal line = Reflecting surfaceIncoming ray with arrow pointing to the surface = Incident ray (AO)Outgoing ray with arrow pointing away from the surface = Reflected ray (OB)Vertical dashed line perpendicular to the surface = Normal (ON)The point where all three lines meet on the surface = Point of incidence (O)Angle between AO and ON = Angle of incidence (i)Angle between OB and ON = Angle of reflection ®
Q20. Laws of Reflection & Verification:Laws of Reflection:The incident ray, the reflected ray, and the normal at the point of incidence always lie in the same plane.The angle of incidence and the angle of reflection are always equal.Verification Activity:Materials required: A drawing board, white sheet of paper, board pins, a plane mirror, a plane mirror holder, a protractor, a pencil, and a ruler.Procedure:Fix the white sheet of paper on the drawing board using board pins.Draw a straight line XY to mark the position of the mirror and place the plane mirror vertically on this line using a holder.Fix two board pins vertically on the paper at points P and Q in front of the mirror.Look into the mirror from the other side and fix two more pins vertically at points R and S such that R, S, and the images of P and Q (P’ and Q’) all lie in a straight line.Remove the pins and mark their positions. Draw line AO passing through P and Q, and line BO passing through R and S.Draw a line ON perpendicular to XY at the point of incidence O.AO represents the incident ray, OB represents the reflected ray, ∠AON is the angle of incidence, and ∠BON is the angle of reflection.Observation: Using a protractor, measuring ∠AON and ∠BON shows that they are equal. Also, the incident ray, reflected ray, and the normal all lie flat on the sheet of paper (same plane).Conclusion: The laws of reflection are verified.Q21. Colour Subtraction Calculations:a. Under White Light:White light is a mixture of Red, Green, and Blue light.The shirt absorbs Red light.Colour subtraction equation:
Since 
, the shirt will reflect green and blue light, making it appear cyan.b. Under Yellow Light:Yellow light is a mixture of Red and Green light.The shirt absorbs Red light.Colour subtraction equation:
The shirt will reflect only green light, making it appear green.
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Answer key
Prepared by: learnloophq@gmail.com
Chapter: 04. Light
ANSWER KEY
SECTION A: MULTIPLE CHOICE QUESTIONS
SECTION B: FILL IN THE BLANKS
SECTION C: TRUE OR FALSE
SECTION D: EXPLAIN AND DIFFERENTIATE TERMS
SECTION E: SHORT ANSWER & DIAGRAM-BASED QUESTIONS
SECTION F: LONG ANSWER QUESTIONS
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