Optics Answers

what is optics

The focal length of a converging lens is 20 cm. The image of the object placed 60 cm from the centre of this lens is real and __________________

You have two plane mirrors of sizes 6 ft and 10 ft. The focal length of these two
mirrors are

If the focal length of a convex lens is 1 m, what is the maximum thickness of the lens?

An object of size 10cm is kept at a distance of 10cm from a convex lens. If the focal length of the lens is 5cm, the size of the image is

A reflecting, spherical Christmas tree ornament has a diameter of 7.0 cm. A child looks at the ornament from a distance of 28 cm. Describe the image she sees.
Answer: -1.65cm
How? I've tried many methods, even the one on here but am still getting a way different number.

convex mirrors are usually used as

magnifying glasses
driving mirrors
dentist mirror
artist mirror

The box of a pin hole camera, of length L, has a hole of radius a. It is assumed that when the hole is illuminated by a parallel beam of light of wavelength  the spread of the spot (obtained on the opposite wall of the camera) is the sum of its geometrical spread and the spread due to diffraction. The spot would then have its minimum size (say b min) when

why our fingers appeared red when we put it on a torch(mobile torch etc)

how many lines must a grating have, used in the second order and near 550 nano meter, to resolve two lines 0.1 angstrom apart ?