Magnetic Effects of Electric Current — Science STD 10 — Question

A lens is cut into two equal halves: Along the principal axis.
What will be the focallength of each half?

A person can read a book clearly only if he holds it at an arm's length from him. Name the defect of vision:

1. If the person is an old man.
2. If the person is a young man.

How does an electromagnet differ from a permanent magnet?

What is the unit of power of a lens? Define the unit of power of a lens.

Can any source of energy be pollution free? Explain your answer with an example.

Distinguish between the terms ‘overloading’ and ‘short-circuiting ‘ as used in domestic circuits.

A boy with a mouth 5cm wide stands 2m away from a plane mirror. Where is his image and how wide is the image of his mouth?

What is the magnification produced by a rear view mirror fitted in vehicles?

An object is placed at a distance of 6cm from a convex mirror of focal length 12cm. Find the position and nature of the image.

An electric motor takes 5 amperes current from a 220 volt supply line. Calculate the power of the motor and electrical energy consumed by it in 2.