Important Questions for Class 8 Science - Light

Q1: How is seeing possible, and why can't we see objects in the dark?
Ans: Seeing is possible when light from an object enters our eyes. We can't see objects in the dark because there is no light to reflect off them.

Q2: What are the laws of reflection, and how do they relate to the angle of incidence and the angle of reflection?
Ans: The laws of reflection state that the angle of incidence is equal to the angle of reflection. These angles are measured with respect to the normal to the reflecting surface.

Q3: Explain why lateral inversion occurs in a mirror image.
Ans: Lateral inversion happens because in a mirror image, the left side of the object appears on the right, and the right side appears on the left, which is a result of how light rays reflect off the mirror.

Q4: Differentiate between regular and diffused reflection. What causes diffused reflection?
Ans: Regular reflection occurs from smooth surfaces like mirrors, forming clear images. Diffused reflection occurs from rough or irregular surfaces, and it results from irregularities in the reflecting surface.

Q5: How do periscopes work, and where are they commonly used?
Ans: Periscopes use two plane mirrors to reflect light and allow people to see objects that are not directly visible. They are commonly used in submarines, tanks, and bunkers.

Q6: What happens when two plane mirrors are placed at an angle to each other, and why is this used in kaleidoscopes?
Ans: Placing two mirrors at an angle to each other creates multiple images. This idea is used in kaleidoscopes to produce various beautiful patterns.

Q7: How does the eye function as a sense organ, and what are the different components of the eye?
Ans: The eye allows us to see by focusing light on the retina, which contains nerve cells. Key components of the eye include the cornea, iris, pupil, lens, and retina.

Q8: Explain the role of the iris in controlling the amount of light entering the eye.
Ans: The iris controls the size of the pupil, which regulates the amount of light entering the eye. In bright conditions, the pupil becomes smaller to reduce the amount of light, and in dim conditions, it enlarges to let in more light.

Q9: What is the function of cones and rods in the retina, and what is the blind spot in the eye?
Ans: Cones sense color and function in bright light, while rods are sensitive to dim light. The blind spot is a spot on the retina where there are no sensory cells, so no vision is possible.

Q10: How does persistence of vision explain the phenomenon of movies and animation?
Ans: Persistence of vision means that the retina retains an image for a fraction of a second. Movies and animation work by displaying a series of separate images rapidly (faster than 16 per second), creating the illusion of motion.

Q11: Why is it important to protect your eyes from excessive or insufficient light, and what precautions should be taken?
Ans: Excessive light can injure the retina, while insufficient light can cause eyestrain and headaches. Precautions include not looking directly at the Sun, avoiding rubbing your eyes, and reading at an appropriate distance.

Q12: How does the deficiency of vitamin A in the diet affect the eyes, and what are some good dietary sources of vitamin A?
Ans: Vitamin A deficiency can lead to eye troubles, including night blindness. Good dietary sources of vitamin A include raw carrots, green vegetables, cod liver oil, eggs, milk, and fruits like papaya and mango.

Q13: How do visually impaired individuals read and write using the Braille system, and what is its significance?
Ans: Visually impaired individuals use the Braille system, which is a tactile system of reading and writing. They recognize characters by touch, and Braille is a valuable resource that enables them to access written information.

Q14: Explain the structure and function of the cornea and lens in the eye's ability to focus light.
Ans: The cornea is the transparent front part of the eye that allows light to enter. The lens, thicker at the center, focuses light on the retina, enabling us to see objects clearly.

Q15: What is cataract, and how is it treated in modern technology?
Ans: Cataract is the clouding of the eye lens, which can lead to blurred vision. Modern technology allows for the removal of the opaque lens and the insertion of an artificial lens to restore clear vision.