PHYSICS [1 Mark Question Answer]

Riveting is a forging process that may be used to join parts together by way of a metal part called a rivet. The rivet acts to join the parts through adjacent surfaces. A straight metal piece is connected through the parts. Then both ends are formed over the connection, joining the parts securely.

It is kept a bit smaller so that while mounting it can be heated and mounted easily and on contracting it will just fix tightly to the wooden wheels but if kept the same diameter as the wheel , it will wull further expand on summers and will come off the wheels.

Pyrex glass tumbler does not crack on adding hot water because Pyrex glass has a low coefficient of expansion. It does not expand less when hot water is added to the tumbler.

When hot water is poured into thick glass tumbler, the inner surface of the tumbler becomes hot and expands. The outer surface of the tumbler does not expand quickly. Due to this uneven expansion, the glass tumbler cracks.

So to allow the expansion and contraction, a small gap is left behind the walls while mounting a girder for roofing.

Bridges are mounted on rollers to prevent their collapse.

A cement floor is not laid out in a single piece. The floor is put in small sections with gaps between them. It is done to avoid cracking of the floor due to expansion in summer and contraction in winter.

Telephone wires are kept slightly loose when they are laid because heat. Therefore, without a slack they could become too tight and break in winters or pull loose from their anchors in summers . This is the reason why wires are kept slightly loose when they are laid.

These gaps which are of the order of a few millimeters, are provided to allow room for the rails to expand the rise in temperature due to the atmospheric temperature as well as the friction caused by running of train. All materials expand when heated and contract when cooled.

An automatic fire alarm in a building’s security system is a heat detector that responds to the heat from a fire by setting off an alarm. Some heat detecting fire alarms rely on a bimetallic strip as the temperature sensor. This strip responds to heat by closing a normally open electrical circuit to activate the alarm.

Ball and Ring Experiment: This well known experiment shows that the solids expand on heating and contract on cooling. The apparatus consists of a metallic ball and ring such that at room temperature the ball just passes through the ring.

Liquids and gases occupy the same shape of vessel. They do not have individual length and area. Hence, liquids and gases have no linear and areal expansions.

Cubical Expansion: The increase in the volume of a substance (solid, liquid, or gas) when heated, is called cubical expansion.

Superficial expansion is a type of thermal expansion in which whenever a solid is heated, its surface area increases. This type of expansion is known as superficial expansion or area expansion.

Expansion means to change or increase in length. If the change in length is along one dimension (length) over the volume, it is called linear expansion.

Thermal expansion is the tendency of matter to change in volume in response to temperature alterations. When a substance is heated, its particles move more and thus maintain a greater average separation. Since thermosets are used in solid form they undergo linear thermal expansion.

Evaporation is the process in which water evaporates from the liquid surface and changes into a gaseous state by the action of heat. It plays a very important role water cycle.

Boiling Point is the temperature at which liquid starts to boil. It is the temperature at which the vapor pressure of liquids becomes equal to its atmospheric pressure.

New electric wires for power transmission are fixed slightly, if laid during summer. This prevents wires from snapping in winter.

Small gaps are provided between the railway lines to fill gap in summer laying of railway lines.

An iron rim of a slightly smaller diameter than a wooden wheel is cooled so that it easily fit over wooden wheel.

A bimetallic strip expands unequally on heating and bend.

When a flat sheet of copper is heated the increase in its area is called superficial expansion.