Light Reflection and Refraction Test

Result

Light Reflection and Refraction Test - 11

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Weekly Quiz Competition

Question 1
1 / -0

Two thin lenses of power, +3.5 D and, -2.5 D are placed in contact. Find the power of the lens combination.

A
+1.0 D

B
-1.0 D

C
+5.5 D

D
-5.5 D

Solution

If lenses of powers p₁ and p₂ are placed in contact, the power of the combination is given by:

P = p₁ + p₂

P = +3.5 + (-2.5)

P = 3.5 – 2.5

P = +1.0 D
Question 2
1 / -0

Which of the following lens would you prefer to use while reading small letters found in a dictionary?

A
A convex lens of focal length 50cm.

B
A concave lens of focal length 50cm.

C
A convex lens of focal length 5cm.

D
A concave lens of focal length 5cm.

Solution

A convex lens gives a magnified image of an object when it is placed between the radius of curvature and focal length. Also, magnification is more for convex lenses having shorter focal length. Therefore, for reading small letters, a convex lens of focal length 5 cm should be used.
Question 3
1 / -0

A convex lens of focal length 8cm forms a real image of the same size as the object. The distance between the object and its image will be:

A
8cm

B
16cm

C
24cm

D
32cm

Solution

A convex lens forms a real image at 2F on the right side of the lens. The size of the image is equal to that of the object if the object is placed at 2F.

Therefore, the distance between the object and the image = 2f+ 2f = 4f

= 4 × 8 = 32 cm