Which of the following instruments is most suitable for measuring the outside diameter of a narrow pipe in a few millimeters in diameter?

Electrical power is transmitted at a high voltage rather than a low voltage because the amount of energy loss is due to

If the focal length of a camera is 20cm, the distance from the film at which the lens must be set to produce a sharp image of 100cm away is

The image of an object is located 6cm behind a convex mirror. If it's magnification is 0.6, calculate the focal length of the mirror

A lens of focal length 15cm forms an erect image which is three times the size of the object. The distance between the object and the image is ___.