The process of sending back the light rays which fall on the surface of an object, is called reflection of light.
Rules for obtaining images formed by concave mirrors
| object Position | Image Position | Nature of Image | |||||||||
| (a) |
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at infinity | more...
Electricity & Magnetic Effects of Electric Current
Electricity is the identity of modernity. It has really redefined the way of our life. Thus it has an important place in modern society. It is used almost at every place to facilitate modern activities.
Electric Current
Electric current is the rate at which charge passes by a point in the circuit. The magnitude of electric current in a conductor is the amount of electric charge passing through a point of the conductor in one second.
The SI unit of current is ampere.
A current of 1 ampere means that there is 1 coulomb of charge passing through a cross section of a wire in 1 second.
Electric Circuit
Electric circuit is an incessant conducting path that consists of wires, electric bulb and switch between the two terminals of a cell or a battery along which an electric current
Electric Potential (V)
Electric potential at a point is defined as the work done in moving a unit positive charge from infinity to that point. The S.I unit of electric potential is volt.
Electric circuit
Potential Difference
Potential difference is defined as the amount of work done in moving a unit charge from one point to the other point.
\[V\,=\frac{W}{Q}\]
Where, V is potential difference
W is work done
Q is charge moved
Heating Effect of Electric Current
Through a high resistance wire when an electric current is passed, it becomes very hot and produces heat. This phenomenon is known as Heating Effect of current.
\[H={{I}^{2}}RT\]
Where H = heat produced
I = current
R = resistance of wire
T = time, for which current is passed
This is known as Joule's law of heating.
Ohm's Law
Ohm's law represents the relationship between current and potential difference. According to Ohm's law the current flowing through a conductor between two points is directly proportional to the potential difference and inversely proportional to the resistance between them when the temperature and pressure remains the same.
\[V\,\alpha \,I\]
\[V=IR\]
So, \[I=V/R\]
Where, I is the current v is the potential difference R is the resistance.
Electric Power
Electric power is the electric work done per unit time. The S.I unit of electric power is
\[Power=\frac{Work\,done}{Time\,taken}\]
\[P=\frac{W}{t}\]
By substituting from W = VIt, we obtain the formula for the power dissipated in an electric circuit, as follows:
\[Power\,P=VI\]
This formula gives the power which is degenerated when a current I moves through a conductor when there is a potential difference V. From Ohm's law, we can write:
Power \[P={{I}^{2}}R\] and \[P={{V}^{2}}/R\]
Magnetic Field
Magnetic field is the space/region around a magnet in which magnetic force is exerted. Electric current produces magnetic field. The SI unit for magnetic field is Tesla. The strength of magnetic field is more...
Sources of Energy and Natural Resources
Energy is the capacity to do work. Without energy we cannot perform any activities. In our day to day life, we use energy from various sources for doing work.
There are mainly two categories of sources of energy:
(1) Non-Renewable sources of energy
(2) Renewable source of energy
Non-renewable Sources of Energy
Are those sources of energy which cannot be quickly replaced when exhausted For example, fossil fuels, petroleum, etc.
Fossil Fuel
It consists of mainly coal, petroleum and natural gas. It is a non- renewable source of energy It takes millions of years for the formation of fossil fuels. It is formed deep under the earth from the remains of plants and animals. That's why fossil fuel should be wisely and carefully used. Fossil fuels have some disadvantages as well. It causes pollution to disturb the ecological balance of earth.
Nuclear Energy
The energy released during a nuclear reaction is called nuclear energy. This energy can be obtained during nuclear fission and fusion. During nuclear fission, the nucleus of a heavy atom such as uranium, plutonium or thorium is bombarded with low-energy neutrons. The nucleus can be split apart into lighter nuclei. In this process, a large amount of energy is released. During fusion, the two nuclei of light elements such as hydrogen combine to form a heavy nucleus such as helium. In this process a large amount of energy is produced. The nuclear energy can be used to produce electricity on a large scale. If this energy is used carefully and wisely then it can fulfil the requirement of energy needs. This energy has limitations as well. The major hazard of nuclear power generation is the storage and disposal of spent or used radioactive substances. The nuclear hazard can cause destruction on a large scale. It cannot only cause environmental contamination but also huge loss of life and property.
Renewable Sources of Energy
Are those which are inexhaustible and being produced continuously in nature. The sources of energy are also known as non-conventional sources of energy. For example wind, tides, sun, etc.
Wind Energy
The air in the atmosphere that is in motion is called wind. The wind possesses kinetic energy. Wind turbines convert the kinetic energy in the wind into mechanical energy. Wind is caused by uneven heating of the atmosphere by the sun, variations in the earth’s surface and rotation of earth. Wind turbines produce electricity by rotating propeller like blades around a rotor.
Biomass
Biomass is a major source of energy. It is produced from the dung of animals, firewood agricultural residues such as bagasse and crop stalks. The dead parts of plants, trees and the waste material of animals are called biomass.
The following are the various applications of biomass that are widely in use
Our Environment
The environment is the physical surrounding around us that includes biotic and abiotic components such as plants, animals, human beings, microorganisms, water, soil, air, etc. These all are interdependent and cannot survive without each other. Human being is the only organism who can cause imbalance in natural environment because of their greed. A balanced environment is necessary for the proper growth of all forms of life.
Ecosystem and Its Components
An ecosystem consists of all the biotic factors such as plants, animals and microorganisms and abiotic factors such as soil, air and water, etc. In an area, these all factors function together. The following are the examples of ecosystems:
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(a) 1728 (b) 1331
(c) 729 (d) 512
(e) None of these
Answer (b)
Explanation: Here the pattern is ________
\[{{(18+10+8)}^{{}^{3}/{}_{2}}}=216\],
\[{{(15+12+22)}^{{}^{3}/{}_{2}}}=343\],
\[{{(57+43+21)}^{{}^{3}/{}_{2}}}=1331\]
Direction Sense Problems
In such types of problems, we draw a diagram by using the given information. The following diagram shows all the Direction in a proper manner.
Example:
If P is to the north of Q and R is to the west of Q, then in which direction is P with respect to R?
(a) North-east (b) South-west
(c) North (d) South
(e) None of these
Answer (a)
Explanation: Clearly from the diagram it is clear that P is
In north –east direction with respect to R.
Blood-Relations Problems
In such types of problems, we should first be clear on the relations given in the following table:
Mother's father \[\to \]Maternal grand father
Mother's mother \[\to \] Maternal grand mother
Husband of aunt\[\to \] Uncle
Wife of maternal uncle\[\to \] Maternal aunt
Mother's brother \[\to \]Maternal uncle
Mother's sister \[\to \] Maternal aunt
Children of maternal uncle/aunt \[\to \]Cousins
Father's father \[\to \]Paternal grand father
Father's mother \[\to \]Paternal grand mother
Father's brother \[\to \]Uncle
Father's sister \[\to \]Aunt
Children of uncle \[\to \]Cousins
Example:
Pointing at a photo, A man said, "His father is the only Son of my mother”. The man has a relation from the Person in the photo is of________
(a) Uncle (b) Grandfather
(c) Father (d) Cousin
(e) None of these
Answer (c)
Explanation:
Figure Based Problems
In such types of problems, a series of figures is given which Proceeds with a certain rule or pattern
Example:
Find the figure which comes next in the series.
(a) 
(b) 
(c) 
(d) 
(e) None of these
Answer (b)
Explanation: Each next figure rotates \[45{}^\circ \] anticlockwise in each block and one line is added to its top and Bottom alternatively.
Hence the answer figure is (b). 
