Write an expression for the work done
[question] Question. Write an expression for the work done when a force is acting on an object in the direction of its displacement. [/question] [solution] Solution: Work done = Force × Displacement or W = F × s [/solution]...
Read More →Two lamps, one rated 100 W at 220 V
[question] Question. Two lamps, one rated $100 \mathrm{~W}$ at $220 \mathrm{~V}$, and the other $60 \mathrm{~W}$ at $220 \mathrm{~V}$, are connected in parallel to the electric mains supply. What current is drawn from the line if the supply voltage is 220 V ? [/question] [solution] solution: Resistance of first lamp, $R_{1}=\frac{V^{2}}{P}=\frac{(220)^{2}}{100}$ resistance of the second lamp, $\mathrm{R}_{2}=\frac{\mathrm{V}^{2}}{\mathrm{P}}=\frac{(220)^{2}}{60}$ Since the two lamps are connecte...
Read More →Explain the reasons for the French Colonisers to scrap the bounty programme for rat hunting in 1902-
[question] Question. Explain the reasons for the French Colonisers to scrap the bounty programme for rat hunting in 1902-03. Or What was the purpose to start the ‘Rat Hunt’ programme by the French in Vietnam in 1902? How the purpose got defeated? Or Describe the ‘Rat Hunt’ activity introduced by the French in Vietnam [/question] [solution] Solution: (1) 1.The modern part of Hanoi was struck by bubonic plague. To fight the plague, French started Rat Hunt programme in 1902. 2.The people were paid ...
Read More →When do we say that work is done ?
[question] Question. When do we say that work is done ? [/question] [solution] Solution: Work is said to be done when: (i) a force should act on an object, and (ii) the object must be displaced. [/solution]...
Read More →India has had a long and unbroken tradition of great scholarship — in mathematics, astronomy, linguistics, logic and ethics.
[question] Question India has had a long and unbroken tradition of great scholarship — in mathematics, astronomy, linguistics, logic and ethics. Yet, in parallel with this, several superstitious and obscurantist attitudes and practices flourished in our society and unfortunately continue even today — among many educated people too. How will you use your knowledge of science to develop strategies to counter these attitudes? [/question] [solution] Solution Poverty and illiteracy are the two main f...
Read More →Compare the power used in the $2 \Omega$ resistor in cach of the following circuits:
[question] Question. Compare the power used in the $2 \Omega$ resistor in each of the following circuits: (i) a $6 \mathrm{~V}$ battery in series with $1 \Omega$ and $2 \Omega$ resistors, and (ii) a $4 \mathrm{~V}$ battery in parallel with $12 \Omega$ and $2 \Omega$ resistors. [/question] [solution] solution: (i) Since $6 \mathrm{~V}$ battery is in series with $1 \Omega 2$ and $2 \Omega \Omega$ resistors, current in the circuit, $I=\frac{6}{1+2}=\frac{6}{3}=2 \mathrm{~A}$ Power used in $2 \Omega...
Read More →A force of 7 N acts on an object. The displacement is,
[question] Question. A force of 7 N acts on an object. The displacement is, say 8 m, in the direction of the force (see fig.). Let us take it that the force acts on the object through the displacement. What is the work done in this case ? [/question] [solution] Solution: Given, force = 7 N ; displacement = 8 m Work done = Force × Displacement $=7 \times 8=56 \mathbf{J}$ [/solution]...
Read More →How did the long war between the US and Vietnam come to an end ?
[question] Question. How did the long war between the US and Vietnam come to an end ? Describe. [/question] [solution] Solution: 1.The US failed to achieve its objective. Vietnam’s resistance could not be crushed. 2.It proved costly to the US. There were high casualties on the US side. 3.It was the first war shown on television. Battles were shown on the daily news world over. 4.People were disillusioned with the US and its policy of war was criticized. 5.Widespread questioning of government pol...
Read More →Science, like any knowledge, can be put to good or bad use, depending on the user. Given below are some of the applications of science.
[question] Question Science, like any knowledge, can be put to good or bad use, depending on the user. Given below are some of the applications of science. Formulate your views on whether the particular application is good, bad or something that cannot be so clearly categorized: (a) Mass vaccination against small pox to curb and finally eradicate this disease from the population. (This has already been successfully done in India). (b) Television for eradication of illiteracy and for mass communi...
Read More →How was the idea of “looking modem” implemented in Tonkin Free School ? Explain.
[question] Question. How was the idea of “looking modem” implemented in Tonkin Free School ? Explain. [solution] Solution: 1.Students were suggested to adopt the Western-style of education. 2.This education included classes in science, hygiene, and French. 3.Traditionally, Vietnamese youths kept long hair. They were asked to cut their hair short. 4.These schools encouraged students to wear western clothes to play western games. 5.French promoted the youths to study Western customs [/solution]...
Read More →The volume of a 500 g sealed packet
[question] Question. The volume of a $500 \mathrm{~g}$ sealed packet is $350 \mathrm{~cm}^{3}$. Will the packet float or sink in water if the density of water is $1 \mathrm{~g} \mathrm{~cm}^{3}$ ? What will be the mass of the water displaced by this packet ? [/question] [solution] Solution: Given, mass of sealed packet, m = 500 g ; volume, $\mathrm{V}=350 \mathrm{~cm}^{3} ;$ density, $\rho=?$ density of water, $\rho_{w}=1 \mathrm{~g} \mathrm{~cm}^{-3}$ Density $=\frac{\text { Mass }}{\text { Vol...
Read More →Several electric bulbs designed to be used on a 220 V electric supply line,
[question] Question. Several electric bulbs designed to be used on a 220 V electric supply line, are rated 10 W. How many lamps can be connected in parallel with each other across the two wires of 220 V line, if the maximum allowable current is 5 A ? [/question] [solution] solution: Resistance of each bulb, $R=\frac{V^{2}}{P}=\frac{(220)^{2}}{10}=4840 \Omega$ Total resistance in the circuit, $\mathrm{R}_{*}=\frac{220}{5}=44 \Omega$ Let $\mathrm{n}$ be the number of bulb (each of resistance $\mat...
Read More →To counter the Chinese influence what steps did the French take in the sphere of education?
[question] Question. To counter the Chinese influence what steps did the French take in the sphere of education? What were the two broad opinions on this question? [CBSE 2012] [/question] [solution] Solution: (1) To counter Chinese influence, the French took the following steps: 1.They dismantled the traditional education system of Vietnam. 2.They established French school of Vietnamese. 3.They propagated Western culture among Vietnamese youths. 4.The few who learnt French and acquired French cu...
Read More →The volume of 50 g of a substance
[question] Question. The volume of $50 \mathrm{~g}$ of a substance is $20 \mathrm{~cm}^{3}$. If the density of water is $1 \mathrm{~g} \mathrm{~cm}^{-3}$, will the substance float or sink in water ? [/question] [solution] Solution: Given, mass of substance, $m=50$ g; volume, $\mathrm{V}=20 \mathrm{~cm}^{3} ;$ density, $\rho=?$ Density $=\frac{\text { Mass }}{\text { Volume }}=\frac{50}{20}=2.5 \mathrm{~g} \mathrm{~cm}^{-3}$ The density of the substance is more than the density of water $\left(1 ...
Read More →Show how you would connect three resistors,
[question] Question. Show how you would connect three resistors, each of resistance $6 \Omega$, so that the combination has a resistance of (i) $9 \Omega$ (ii) $2 \Omega$. [/question] [solution] solution: (i) In order to get a resistance of $9 \Omega$ from three resistors, we connect two $6 \Omega$ resistors in parallel and this parallel combination in series with the third $6 \Omega$ resistor as shown in fig. Two $6 \Omega$ resistors are in parallel, their equivalent resistance is, $\mathrm{R}_...
Read More →Attempt to formulate your ‘moral’ views on the practice of science. Imagine yourself stumbling upon a discovery,
[question] Question Attempt to formulate your ‘moral’ views on the practice of science. Imagine yourself stumbling upon a discovery, which has great academic interest but is certain to have nothing but dangerous consequences for the human society. How, if at all, will you resolve your dilemma? [/question] [solution] Solution A scientist works for the truth. Every scientific discovery reveals a certain truth of nature. Any discovery, bad or good for humanity, must, therefore, be made public. But ...
Read More →Why does a block of plastic released under water come up to the surface of water ?
[question] Question. Why does a block of plastic released under water come up to the surface of water ? [/question] [solution] Solution: Density of plastic block is less than the density of water. Thus, when it floats, it is partially immersed in water such that its weight gets balanced with the buoyant force acting on it. When it is put completely in water, buoyant force on it becomes more than its weight. Thus, when it is released, it comes up to the surface of the water due to a net upward fo...
Read More →How did the textbooks represent Vietnamese during the period of French colonization?
[question] Question. How did the textbooks represent Vietnamese during the period of French colonization? Explain. [CBSE 2014] [/question] [solution] Solution: 1.School textbooks glorified the French and justified colonial rule while Vietnamese were represented as primitive and backward. 2.They were capable of manual labour but not of intellectual reflection. 3.They could work in the fields but not rule themselves. 4.They were ‘skilled copyists’ but not creative. 5.School children were told that...
Read More →In what direction does the buoyant force on an object immersed in a liquid act ?
[question] Question. In what direction does the buoyant force on an object immersed in a liquid act ? [/question] [solution] Solution: An object immersed in a liquid experiences a buoyant force in upward direction. [/solution]...
Read More →How many $176 \Omega$ resistors (in parallel) are
[question] Question. How many $176 \Omega$ resistors (in parallel) are required to carry $5 \mathrm{~A}$ in $220 \mathrm{~V}$ line? [/question] [solution] solution: Here, $I=5 \mathrm{~A}, \mathrm{~V}=220 \mathrm{~V} .$ Resistance required in the circuit, $\mathrm{R}=\frac{\mathrm{V}}{\mathrm{I}}=\frac{220 \mathrm{~V}}{5 \mathrm{~A}}=44 \Omega$ Resistance of each resistor, $\mathrm{r}=176 \Omega$ If $\mathrm{n}$ resistors, each of resistance $\mathrm{r}$, are connected in parallel to get the req...
Read More →What was Phan Chu Trinh’s objective for Vietnam ? How were his ideas different from those of Phan Boi Chau
[question] Question. What was Phan Chu Trinh’s objective for Vietnam ? How were his ideas different from those of Phan Boi Chau ? [CBSE March 2011] [/question] [solution] Solution: Both Phan Boi Chau and Phan Chau Trinh were Vietnamese nationalists to the core. Both were absolutely anti-colonialists and worked to free Vietnam from the French domination. Chau and Trinh, both wanted to modernise Vietnam. In short, both Chau and Trinh were looking at the same end – a free sovereign modern Vietnam. ...
Read More →A ball thrown up vertically returns to the thrower after 6 s. Find.
[question] Question. A ball thrown up vertically returns to the thrower after 6 s. Find. (a) the velocity with which it was thrown up (b) the maximum height it reaches, and (c) its position after 4 s (take g = 10 m/s2) [/question] [solution] Solution: (a) The ball returns to the thrower in 6 s, thus, the time for its upward journey = 6 ÷ 2 = 3 s For the upward motion of ball, initial velocity u = ? ; final velocity v = 0 ( $\because$ Ball comes to rest) Time, t = 3 s Acceleration due to gravity,...
Read More →A battery of 9 V is connected with resistors
[question] Question. A battery of $9 \mathrm{~V}$ is connected with resistors of $0.2 \Omega, 0.3 \Omega, 0.4 \Omega, 0.5 \Omega$ and $12 \Omega$ in series. How much current would flow through the $12 \Omega$ resistor? [/question] [solution] solution: Since all the resistors are in series, equivalent resistance, $R_{\varepsilon}=0.2+0.3+0.4+0.5+12=13.4 \Omega$ Current, $\mathrm{I}=\frac{\mathrm{V}}{\mathrm{R}_{2}}=\frac{9}{13.4}=0.67 \mathrm{~A}$ In series, same current (I) flows through all the...
Read More →Write in about 1000 words a fiction piece based on your speculation on the science and technology of the twenty-second century
[question] Question Write in about 1000 words a fiction piece based on your speculation on the science and technology of the twenty-second century. [/question] [solution] Solution Imagine that you are in a spaceship, along with your friends, moving towards Mars. The spaceship's body is made of a specially constructed material that gets hard as its temperature increases. This spacecraft uses nuclear fuel and three nuclear power plants which are located in a spacecraft. Alternatively, two of them ...
Read More →When a 12 V battery is connected across an
[question] Question. When a 12 V battery is connected across an unknown resistor, there is a current of 2.5 mA in the circuit. Find the value of the resistance of the resistor. [/question] [solution] solution: Here, $\mathrm{V}=12 \mathrm{~V}, \mathrm{I}=2.5 \mathrm{~mA}=2.5 \times 10^{-3} \mathrm{~A}$ Resistance of the resistor, $\mathrm{R}=\frac{\mathrm{V}}{\mathrm{l}}=\frac{12}{2.5 \times 10^{-3}}$ $=4800 \Omega=4.8 \mathrm{k} \Omega$ [/solution]...
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