1. Explain the shining of an air bubble in water.
2. A convex lens forms an image of the same size as the object at a distance of 30 cm from the lens. What is the distance of the object from the lens? [5 MARKS]
1. Explain the shining of an air bubble in water.
2. A convex lens forms an image of the same size as the object at a distance of 30 cm from the lens. What is the distance of the object from the lens? [5 MARKS]
Each point: 1 Mark
Problem: 3 Marks
1. For water – air interface, the critical angle is 48.80. When light is travelling in water, it is incident at an angle greater than 48.8o, therefore light suffers total internal reflection inside the bubble. So the air bubbles in water shine brilliantly
2. A convex lens forms the image of the same size as the object only when the object is placed at a distance 2f from the lens. In this case the image distance is also equal to 2f from the lens.
Hence, 2f = 30 cm
or f = 15 cm = 0.15 m
Power of the lens, P = 1f = 10.15D = 6.6 D
The distance of the object from the lens is also 2f = 30 cm
Each point: 1 Mark
Problem: 3 Marks
1. For water – air interface, the critical angle is 48.80. When light is travelling in water, it is incident at an angle greater than 48.8o, therefore light suffers total internal reflection inside the bubble. So the air bubbles in water shine brilliantly
2. A convex lens forms the image of the same size as the object only when the object is placed at a distance 2f from the lens. In this case the image distance is also equal to 2f from the lens.
Hence, 2f = 30 cm
or f = 15 cm = 0.15 m
Power of the lens, P = 1f = 10.15D = 6.6 D
The distance of the object from the lens is also 2f = 30 cm
