To do:  We have to define regular polygon and state the name of a regular polygon of(i) 3 sides(ii) 4 sides(iii) 6 sides.Solution:A polygon is a closed plane or two-dimensional figure whose sides are straight line segments.Regular polygon:A regular polygon is a polygon that has equal sides and equal angles.(i) A regular polygon of 3 sides is called an equilateral triangle.(ii) A regular polygon of 4 sides is called a square.(iii) A regular polygon of 6 sides is called regular hexagon.

To do:  We have to find the number of diagonals each of the below shapes have.(a) A convex quadrilateral(b) A regular hexagon(c) A triangle.Solution:(a) A convex quadrilateral is shown below.From the above figure, we can observe that,A convex quadrilateral has two diagonals.(b) A regular hexagon is shown below.From the above figure, we can observe that,A regular hexagon has nine diagonals.(c) A triangle is shown below.From the above figure, we can observe that,A triangle has no diagonals.

To do:  We have to classify each of the given figures on the basis of the following.(a) Simple curve(b) Simple closed curve(c) Polygon(d) Convex polygon(e) Concave polygon.Solution:We know that, Simple curves:Simple curves do not cross or intersect.Simple closed curve:Does not have end points and does not intersect.Polygon:A polygon is a closed plane or two-dimensional figure whose sides are straight line segments. Convex Polygon: A polygon is convex if it contains all the line segments connecting any pair of its points.Concave Polygon: A polygon that is not convex is said to be a concave polygon.Therefore, (a) Figures 1, 2, 5, 6 and 7 are simple ... Read More

Given:$(2x-1,3y+1)$ and $(x+3,y-4)$ are equal ordered pairs.To do:We have to find the values of $x$ and $y$.Solution:We know that,Two ordered pairs are equal if and only if the corresponding first components are equal and the second components are equal. Therefore,$2x-1 = x+3$ and $3y+1 = y-4$$2x-x=3+1$ and $3y-y=-4-1$$x=4$ and $2y=-5$$x=4$ and $y=\frac{-5}{2}$The values of $x$ and $y$ are $4$ and $\frac{-5}{2}$ respectively. 

Correct answer is: $(b)$ a cloudy dayExplanation:A solar water heater is a device that converts solar energy into thermal energy. Without solar energy, it can't work. If a solar heater is used without sunlight, it will not work at all.On a cloudy day:A solar water heater cannot be used to get hot water on a cloudy day because it receives energy from the sun, and on a cloudy day, the sun does not appear.On a sunny day:Whereas on a sunny day the sun appears and a solar water heater converts sunlight energy into heat energy efficiently on a sunny day.On a ... Read More

Correct Answer is : $(c)$ nuclear energyExplanation:Biomass$\rightarrow$Biomass is the organic matter like dead parts of plants and trees and the waste material of animals which are used as a fuel to produce energy. Examples of biomass energy:Wood, agricultural wastes, cow dung, and biogas are some examples of biomass energy.Nuclear energy$\rightarrow$Nuclear energy $(Atomic\ energy)$ is also known as nuclear energy refers to the energy released through fission and fusion of the nucleus of an atom to generate heat and electricity.Examples of Nuclear energy-Solar energy produced due to nuclear fusion and electricity generated by an atomic reactor are examples of nuclear energy.Therefore, nuclear ... Read More

Correct Answer is : $(b)$ geothermal energyExplanation:Geothermal energy$\rightarrow$Geothermal energy is the heat energy obtained from hot rocks present inside the earth due to the fission of radioactive materials in it. So, it does not come directly or indirectly from the sun's energy.The term Geothermal is derived from the two Greek words, 'Geo' meaning "earth" and 'thermal' meaning "heat".Production of geothermal energy$\rightarrow$Geothermal energy is the heat produced deep in the Earth's core, which is a clean, renewable source of energy that can be harnessed for use as heat and electricity. The heat in the core is produced mainly by the radioactive ... Read More

Comparison between the sun and fossil fuels as sources of energy:The SunFossil Fuels1. It produces an enormous amount of heat due to the occurrence of nuclear fusion inside it.1. They are formed from the remains of dead plants and animals.2. It does not cause any air pollution.2. They cause air pollution by burning.3. It is a renewable source of energy.3. They are non-renewable sources of energy.

Comparison and contrast between biomass and hydroelectricity as sources of energy are as follow:Biomass Hydroelectricity 1. It is generated from organic matter including wood, agricultural waste and cow dung.1. It is produced from the potential energy of water stored at a height.2. It is a renewable source of energy.2. It is also a renewable source of energy.3. It can be used for only heating and cooking.3. It can be used for running all types of electrical appliances.4. It can be obtained without using any special device.4. It can be produced only by establishing a hydro-power plant.5. Its burning causes air pollution.5. It does not cause any pollution.Read More

Wind:The wind is the flow of air and is a source of energy. It possesses kinetic energy. Wind possesses kinetic energy, and when the fast-moving wind strikes the wind turbine it starts rotating, thus the kinetic energy of wind is converted into mechanical energy. Further, the wind turbine is connected to electricity generators through the shaft, due to which it also rotates and drives the generator which produces electricity. Finally, the mechanical energy gets converted into electrical energy.Advantages of wind energy:The two advantages of using wind energy for generating electricity are as follows:1. It is a clean source of energy as it ... Read More