The focal length of a concave mirror with radius of curvature of 20 cm will be-

Which combination of colour is the most convenient during day and night time?

A. Orange and blue

B. White and black

C. Yellow and blue

D. Red and green

Lenses with two focal lengths are used by persons suffering from . . . . . . . .

A. Myopia and hypermetropia

B. Myopia or hypermetropia

C. Myopia but not hypermetropia

D. Hypermetropia but not myopia

Which one of the following statements regarding lenses is not correct?

A. A convex lens produces both real and virtual images

B. A concave lens produces both real and virtual images

C. A convex lens can produce images equal, greater and smaller than the size of the object

D. A concave lens always produces images smaller than the size of the object

Consider the following statements.
1. If a person looks at a coin which is in a bucket of water, the coin will appear to be closer than it really is.
2. If a person under water looks at a coin above the water surface, the coin will appear to be at a higher level than it really is.
Which of the above statements is/are correct?

A. Both 1 and 2

B. Only 1

C. Only 2

D. Neither 1 nor 2