Solution:
Watt is the SI unit of power.

Solution:
Sound cannot travel through a perfect vacuum. A vacuum is an area without any air, like space. So sound cannot travel through space because there is no matter for the vibration to work in.

Solution:
A transformer is used to decrease or increase AC voltage.

Solution:
The centre of mass of a body or a system of particles is defined as a single point at which the whole mass of the body or system is imagined to be concentrated and all the applied forces acts at that point. It is that point that moves when forces are applied on the body.

Solution:
According to the Principle of Flotation, when a body is immersed in a fluid, two forces act on it: (1) The weight of the body acting vertically downward through the centre of gravity of the body, and (2) The upthrust of the fluid acting vertically upward through the centre of gravity of the fluid displaced, i.e., centre of buoyancy. The upthrust is also termed as buoyant force.

Solution:
Since the strips are welded together, the combined strip will bend towards left ( towards iron ) since copper strip will have more length than the iron strip.

Solution:
Cover of the solar cooker is made of glass because glass allows the sunlight to pass through it and concentrate at one focal point, it also prevents heat to escape out of the cooker.