What is power of a combination of lenses in contact ?

Obtain an expression for focal length of a combination of thin lenses in contact.

A simple microscope is a combination of two lenses in contact of powers +15 D and +5D. Calculate the magnifying power of the microscope, if the final image is formed at 25 cm from the eye.

A convex lens of power 5 D and a concave lens of power 7.5 D are placed in contact with each other. What is the: a) power of this combination of lenses? b) focal length of this combination of lenses?

The focal length of the combination of two thin lenses in contact is 80 cm. If the focal length of one lens is -20 cm, what is the power of the other lens ?

A convex lens of power +5 D is placed in contact with a concave lens of power -4 D. What is the power of combination and nature of lens combination ?

If two lense with focal lengths 10 cm and -20 cm respectively are kept in contact with each other, what will be the effective power of the combination of the lenses ?

The power of a converging lens is 4.5 D and that of a diverging lens is 3 D. The power of this combination of lenses placed close together is:

Shashank went to the optician to get his eyes checked. He observed that the doctor combined two lenses and put these in front of his eyes so that he could see clearly. The powers of the two lenses used in the combination were -3 D and 4 D. What type of lens will the combination of lenses be?