a) Explain the shining of an air bubble in water.
b) 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? What is the power of the lens? [5 MARKS]
a) Explain the shining of an air bubble in water.
b) 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? What is the power of the lens? [5 MARKS]
part a): 2 Marks
part b): 3 Marks
a) For water-air interface, the critical angle is 48.6∘
When light travelling in water, it is incident at an angle greater than 48.8∘, the light suffers total internal reflection. So the air bubble in water shines brilliantly
b) 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 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
part a): 2 Marks
part b): 3 Marks
a) For water-air interface, the critical angle is 48.6∘
When light travelling in water, it is incident at an angle greater than 48.8∘, the light suffers total internal reflection. So the air bubble in water shines brilliantly
b) 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 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
