State the principle of electric generator.
[question] Question. State the principle of electric generator. [/question] [solution] solution: It is based on the principle of electromagnetic induction, that is, the changing magnetic field induces current in the coil. [/solution]...
Read More →The potential energy of a freely falling object decreases progressively.
[question] Question. The potential energy of a freely falling object decreases progressively. Does this violate the law of conservation of energy ? Why ? [/question] [solution] Solution: It does not violate the law of conservation of energy. The decrease in potential energy due to loss of height, increases the kinetic energy due to gain in speed such that total energy remains constant [/solution]...
Read More →Explain different ways to induce
[question] Question. Explain different ways to induce current in a coil. [/question] [solution] solution: (i) By moving a bar magnet towards or away from the coil. (ii) By placing a coil near another coil which carries a variable current. [/solution]...
Read More →Imagine that you have been asked to write an article for an encyclopaedia on Britain and the history of cotton.
[question] Question. Imagine that you have been asked to write an article for an encyclopaedia on Britain and the history of cotton. Write your piece using information from the entire chapter. [/question] [solution] Solution: Britain and the History of Cotton During the seventeenth and eighteenth centuries, merchants would trade with rural people in textile production. A clothier would buy wool from a wool stapler, carry it to the spinners, and then, take the yarn to the weavers, fuller and dyer...
Read More →A mass of 10 kg is at a point A on a table.
[question] Question. A mass of 10 kg is at a point A on a table. It is moved to a point B. If the line joining A and B is horizontal, what is the work done on the object by the gravitational force ? Explain your answer. [/question] [solution] Solution: The work done is zero. This is because the gravitational force and displacement are perpendicular to each other. [/solution]...
Read More →What is the role of the split-ring
[question] Question. What is the role of the split-ring in an electric motor? [/question] [solution] solution: The split-ring in an electric motor reverses the direction of current in the coil of the motor. Therefore, the direction of the force acting on the two arms of the coil is also reversed. As a result of this, the coil of d.c. motor continues to rotate in the same direction. [/solution]...
Read More →Certain force acting on a 20 kg mass changes its velocity
[question] Question. Certain force acting on a $20 \mathrm{~kg}$ mass changes its velocity from $5 \mathrm{~ms}^{-1}$ to $2 \mathrm{~ms}^{-1}$. Calculate the work done by the force. [/question] [solution] Solution: Given, mass, $\mathrm{m}=20 \mathrm{~kg}$; initial velocity, $\mathrm{u}=5 \mathrm{~ms}^{-1}$; final velocity, $\mathrm{v}=2 \mathrm{~ms}^{-1}$ Work done by the force = change in kinetic energy or $W=\frac{1}{2} m v^{2}-\frac{1}{2} m u^{2}=\frac{1}{2} m\left(v^{2}-u^{2}\right)$ or $\m...
Read More →What is the principle of electric motor ?
[question] Question. What is the principle of electric motor ? [/question] [solution] solution: It is based on the principle that a current-carrying coil experiences equal and opposite forces on its edges which rotates it continuously [/solution]...
Read More →State Fleming's left hand rule.
[question] Question. State Fleming's left hand rule. [/question] [solution] solution: ‘Stretch the thumb, forefinger and central finger of your left hand such that they are mutually perpendicular. If the fore finger points in the direction of magnetic field and the central finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor’. [/solution]...
Read More →A battery lights a bulb.
[question] Question. A battery lights a bulb. Describe the energy changes involved in the process. [question] [solution] Solution: Within the electric cell of the battery, the chemical energy changes into electric energy. The electric energy on flowing through the filament of the bulb, first changes into heat energy and then into the light energy. [/solution]...
Read More →A positively charged particle (alpha particle),
[question] Question. A positively charged particle (alpha particle), projected towards west, is deflected towards north by a magnetic field. The direction of magnetic field is (1) towards south (2) towards east (3) downward (4) upward [/question] [solution] solution: By applying Fleming’s left hand rule, we find that the magnetic field is in upward direction. Thus, option (4) is correct. [/solution]...
Read More →How did the East India Company procure regular supplies of cotton and silk textiles from Indian weavers?
[question] Question. How did the East India Company procure regular supplies of cotton and silk textiles from Indian weavers? [question] [solution] Solution: After establishing political power, the East India Company successfully procured regular supplies of cotton and silk textiles from Indian weavers via a series of actions. These actions were aimed at eliminating competition from other colonial powers, controlling costs and ensuring regular supplies of cotton and silk goods for Britain. First...
Read More →Why did some industrialists in nineteenth-century Europe prefer hand labour over machines?
[question] Question. Why did some industrialists in nineteenth-century Europe prefer hand labour over machines? [question] [solution] Solution: Some industrialists in nineteenth-century England preferred hand labour over machines because there was no labour shortage in the market, and as a result, there was no problem of high wage costs either. Industrialists did not wish to replace hand labour with machines that would require large capital investment. Also, in industries where the production an...
Read More →An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground.
[question] Question. An object thrown at a certain angle to the ground moves in a curved path and falls back to the ground. The initial and the final points of the path of the object lie on the same horizontal line. What is the work done by the force of gravity on the object? [/question] [solution] Solution: The object returns to its level of projection, therefore displacement is in horizontal direction, while force of gravity acts in vertically downward direction. Thus, force and displacement a...
Read More →Textbooks on science may give you a wrong impression that studying science is dry and all too serious and that
[question] Question Textbooks on science may give you a wrong impression that studying science is dry and all too serious and that scientists are absent-minded introverts who never laugh or grin. This image of science and scientists is patently false. Scientists, like any other group of humans, have their share of humorists, and many have led their lives with a great sense of fun and adventure, even as they seriously pursued their scientific work. Two great physicists of this genre are Gamow and...
Read More →In activity 13.7,
[question] Question. In activity 13.7, how do we think the displacement of rod PQ will be affected if (i) current in rod PQ is increased (ii) a stronger horseshoe magnet is inserted (iii) length of the rod PQ is increased. [/question] [solution] solution: (i) When current in rod increases, force on the rod also increases. Hence, the displacement of the rod increases. (ii) When a stronger horseshoe magnet is inserted, magnetic field increases. Thus, force on the rod also increases. Hence, displac...
Read More →Explain what is meant by proto-industrialisation.
[question] Question. Explain what is meant by proto-industrialisation. [/question] [solution] Solution: Proto-industrialisation is the phase of industrialisation that was not based on the factory system. Before the coming of factories, there was large-scale industrial production for an international market. This part of industrial history is known as proto-industrialisation. [/solution]...
Read More →Look at the activities listed below.
[question] Question. Look at the activities listed below. Reason out whether or not work is done in the light of your understanding of the term 'work'. (a) Suma is swimming in a pond. (b) A donkey is carrying a load on its back. (c) A wind-mill is lifting water from a well. (d) A green plant is carrying out photosynthesis. (e) An engine is pulling a train. (f) Food grains are getting dried in the sun. (g) A sailboat is moving due to wind energy. [/question] [solution] Solution: (a) Work is done ...
Read More →Which of the property a proton can change
[question] Question. Which of the property a proton can change when it moves freely in a magnetic field ? (There may be more than one correct answer) (1) mass (2) speed (3) velocity (4) momentum [/question] [solution] solution: Motion of a charged particle like proton in a magnetic field is a circular path. Hence, its velocity and momentum can change. Thus, option (3) and (4) are correct. [/solution]...
Read More →Write True or False against each statement:
[question] Question. Write True or False against each statement: (a) At the end of the nineteenth century, 80 per cent of the total workforce in Europe was employed in the technologically advanced industrial sector. (b) The international market for fine textiles was dominated by India till the eighteenth century. (c) The American Civil War resulted in the reduction of cotton exports from India. (d) The introduction of the fly shuttle enabled handloom workers to improve their productivity. [/ques...
Read More →Explain the following (a) Women workers in Britain attacked the Spinning Jenny.
[question] Question. Explain the following: (a) Women workers in Britain attacked the Spinning Jenny. (b) In the seventeenth century merchants from towns in Europe began employing peasants and artisans within the villages. (c) The port of Surat declined by the end of the eighteenth century. (d) The East India Company appointed gomasthas to supervise weavers in India. [/question] [solution] Solution: (a) Women workers in Britain attacked the Spinning Jenny because it speeded up the spinning proce...
Read More →Define average power.
[question] Question. Define average power [/question] [solution] Solution: The ratio of the total work done or total energy consumed to the total time taken is called average power. $P_{\text {average }}=\frac{\text { total work done }}{\text { total time taken }}$ The concept of average power is useful when the power of a device varies with time. [/solution]...
Read More →Though the statement quoted above may be disputed, most physicists do have a feeling that the great laws of physics
[question] Question Though the statement quoted above may be disputed, most physicists do have a feeling that the great laws of physics are at once simple and beautiful. Some of the notable physicists, besides Dirac, who have articulated this feeling, are Einstein, Bohr, Heisenberg, Chandrasekhar and Feynman. You are urged to make special efforts to get access to the general books and writings by these and other great masters of physics. (See the Bibliography at the end of this book.) Their writ...
Read More →Choose the correct option.
[question] Question. Choose the correct option. The magnetic field inside a long straight solenoid carrying current (1) is zero (2) decreases as we move towards its ends (3) increases as we move towards its ends (4) is the same at all points [/question] [solution] solution: The magnetic field inside a long straight solenoid carrying current decreases as we move towards its ends. At the ends of solenoid, the strength of the magnetic field is almost the half that in the middle of the solenoid. Thu...
Read More →A lamp consumes 1000 J of electrical energy in 10 s.
[question] Question. A lamp consumes 1000 J of electrical energy in 10 s. What is its power ? [/question] [solution] Solution: Power $=\frac{\text { Energy }}{\text { Time }}=\frac{1000}{10}=100 \mathbf{W}$ [/solution]...
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