Derive the expression for the power of two thin lenses placed in contact with each other.

What are the uses of putting two lenses in contact with each other ?

The objective and eye pieces used in a compound microsciope are not single lenses but are the combinations of more than one lenses placed in contact with each other. Explain why?

Fill in the blank Friction opposes the ……….between the surfaces in contact with each other.

Derive an expression for average power of an AC (alternating current) circuit.

Derive an expression for average power in an LCR a.c. circuit.