Search Previous Year Questions

CONCEPT:

• All measurable quantities are divided into two broad categories:

Solution: 

Power is the amount of energy transferred or converted per unit of time. It is a scalar quantity. It is work done per unit of time.

    \(P= \frac{\mathrm{d} W}{\mathrm{d} t} = \frac{\mathrm{d} (F.x)}{\mathrm{d} t} =F \frac{\mathrm{d} x}{\mathrm{d} t}\) ​

         \(P= F.v \)     ...................................................................................(1)​

Where P = Power , W = work done, x = Displacement, v = Velocity

Let Dimension of Power = \([M^{a}L^{b}T^{c}]\)

From equation (1), by equating the dimension of LHS expression to RHS expression.

\([M^{a}L^{b}T^{c}]= [M^{1}L^{1}T^{-2}][M^{0}L^{1}T^{-1}]\)

\([M^{a}L^{b}T^{c}]= [M^{1}L^{2}T^{-3}]\)

Comparing the power of fundamental quantity on both side we get,

a = 1, b = 2, c = - 3 

\(\therefore \) Dimension of Power = \([M^{1}L^{2}T^{-3}]\)

Explanation:

Iron Oxide in brick: 

Iron oxide constituting less than 7 percent of clay imparts the following properties:

1. Gives red color on burning when an excess of oxygen is available and dark brown or even black color when oxygen available is insufficient. However, an excess of ferric oxide makes the brick dark blue. 2. Improves impermeability and durability. 3. Tends to lower the fusion point of the clay, especially if present as a ferrous oxide. 4. Gives strength and hardness.

 Important Points

Silica:

• If it is in proper proportion then there is good cohesion between the particles and imparts uniform shape.
• Excess of silica makes the brick brittle and weak on burning.

Alumina: 

• It imparts plasticity to the brick. Absorbs water and renders the clay plastic. If alumina is present in excess of the specified quantity, it produces cracks in brick on drying.

Lime:

 Lime in brick clay has the following effects:

1. Provide bondage
2. Causes silica in clay to melt on burning and thus helps to bind it.
3. In carbonated form, lime lowers the fusion point.
4. Excess of lime causes the brick to melt and the brick loses its shape.

Explanation: 

Half turn stairs: Half turn stairs are of two types

1. Dog legged stairs 2. Open well stairs

1. Dog legged stairs: It consist of two flight of stairs which are opposite direction, no space is provided between flight in plan.

2. Open well stairs: A half turn stairs with a space between its flight is known as open well stairs. This type of stairs are suitable for multistorey building.

Quarter turn stairs: When direction of flight is changed at right angle either to be left or to be right quarter turn stairs is used. It is suitable when width is more and length is limited.

Three quarter turn stairs: A stair turning through three right angle is known as three quarter turn stairs.

Continuous stairs: A stair which do not have any landing or intermediate newel post are termed as continuous stair.

Concepts:

Vertical Curves are of two types: Summit Curve and Valley Curve

The ideal shape for summit curve is circular because sight distance available throughout its length remains constant. However, if deviation angle is very small, behavior of parabola and circular is same**. Hence, parabola is preferred for summit curves.**

For Valley curves**, cubic parabola** is preferred as introduction of centrifugal force on this curve is gradual and hence, there is no problem of discomfort. However, IRC suggest Square parabola for valley curves due to simplicity of calculation.

Explanation:

Fly Ash

It is a heterogeneous by-product material produced in the combustion process of coal used in power stations. It is a fine grey-colored powder having spherical glassy particles that rise with the flue gases. As fly ash contains pozzolanic materials components which reach with lime to form cementitious materials. Thus Fly ash is used in concrete, mines, landfills, and dams.

Chemical Composition of Fly Ash as follows:

The chemical composition of fly ash depends upon the type of coal used and the methods used for the combustion of coal. Table No 1:  Chemical composition of fly ash of different coals.

Concept:

1. Tricalcium Aluminate: C3A is formed within 24 hours of the addition of water in the cement and is responsible for the maximum evolution of heat of hydration. It is the first compound that is formed after the addition of water and sets early.
2. Tetracalcium aluminoferrite: C4AF is also formed within 24 hours of the addition of water in the cement but its individual contribution to the overall strength of the cement is insignificant.
3. Tricalcium silicate: C3S is formed within a week or so of the addition of water in the cement and is responsible for the early development of the strength of the cement.
4. Dicalcium silicate: C2S is the last compound that is formed after the addition of water in the cement which may require a year or so for its formation. It is responsible for the progressive strength of the cement.

Concept:

A flow duration curve is a plot of discharge against the percent of time the flow was equaled or exceeded. This is known as the discharge frequency curve.

The area under the flow duration curve gives the average daily flow for a given period for which flow duration curve is plotted.

Application:

1. To find out the maximum and minimum flow for a hydroelectric power plant.
2. The shape of a flow-duration curve is used to evaluate the stream and catchment characteristics.
3. A very steep curve means high flow for very short period of time and it would cause flood. On the other hand, flat curve means low flow region and it can sustain the flow.

The flow duration curve is the

These compounds are known as Bogue’s Compounds.

• Tricalcium silicate (C₃S): This is also called as Alite. This is also responsible for the early strength of the concrete. The cement that has more C₃S content is good for cold weather concreting. The heat of hydration is 500 J/Cal. Its proportion is 25 - 50%.
• Dicalcium Silicate (C₂S): This compound will undergo reaction slowly. It is responsible for the ultimate strength of concrete. This is also called as Belite. The heat of hydration is 260 J/Cal. Its proportion is 25 - 40%.
• Tricalcium aluminate (C3A): Celite is the quickest one to react when the water is added to the cement. It is responsible for the flash setting. The increase of this content will help in the manufacture of Quick Setting Cement. The heat of hydration is 865 J/Cal. Its proportion is 5 - 11%.
• Tetra calcium Alumino ferrite (C₄AF): This is called as Felite. The heat of hydration is 420 J/Cal. It has the poorest cementing value but it responsible for long term gain of strength of the cement. Its proportion is 8 - 14%.

Explanation:

Wrought iron

• Wrought iron is a very pure iron where the iron content is of the order of 99.5%.
• It usually contains less than 0.1% carbon and 1 or 2% slag.

Pig iron 

• Pig iron is an intermediate product of the iron industry.
• Pig iron has a very high carbon content, typically 3.8–4.7%, along with silica and other constituents of dross, which makes it very brittle.

Cast iron

• Cast iron is an alloy of iron, carbon and silicon and it is hard and brittle.
• Carbon content in CI may be within 1.7% to 3% and carbon may be present as free carbon or iron carbide Fe3C.

Steel 

• Steel is basically an alloy of iron and carbon in which the carbon content can be less than 1.7% and carbon is present in the form of iron carbide to impart hardness and strength.