Solution:
Gravitational force is maximum at Poles. The gravitational force is almost equal in every where in the earth. The resultant force is maximum in pole.

Solution:
A microscope is an instrument that produces a clear magnified image of an object viewed through it. A basic microscope is made up of two converging lenses. The first lens creates a real image which serves as the object for the second lens, and the image created by the second lens is the one a viewer sees. The final image is virtual and is inverted compared to the original object.

Solution:
Photovoltaic cell converts light energy to electrical energy.

Solution:
When the piece of iron is lowered into the water, the water level in the bucket increases. And so the pressure at the bottom of bucket also increases. Thus the total thrust at the bottom also increases. Therefore the spring balance reading increases.

Solution:
450 mm Hg denotes the air pressure.

Solution:
A motion that repeats itself after equal intervals of time is known as periodic motion. Examples of periodic motion are a tuning fork or motion of a pendulum if you analyze the motion you will find that the pendulum passes through the mean position only after a definite interval of time.

Solution:
The specific heat of water is higher than all other common substances. Hence, water is used for heating purposes (as in hot water bottles) and for cooling purposes (as in radiators of cars). Off all the liquids, mercury has the lowest specific heat due to which it is used as a thermometric liquid .