Class 12

Write a short note on
(a) Adaptations of desert plants and animals

(b) Adaptations of plants to water scarcity

(c) Behavioral adaptations in animals

(d) Importance of light to plants

(e) Effect of temperature or water scarcity and the adaptations of animals.

Solution: (a) Adaptations of desert plants and animals Desert plants: The blazing heat and shortage of water are two of the most severe conditions found in deserts. Desert plants have adapted to...

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It is now established that protons and neutrons (which constitute nuclei of ordinary matter) are themselves built out of more elementary units called quarks. A proton and a neutron consist of three quarks each. Two types of quarks, the so called ‘up’ quark (denoted by u) of charge + (2/3) e, and the ‘down’ quark (denoted by d) of charge (–1/3) e, together with electrons build up ordinary matter. (Quarks of other types have also been found which give rise to different unusual varieties of matter.) Suggest a possible quark composition of a proton and neutron.

Solution: Given, the net charge of a proton is +e. The value +e can be got when $p=\left(\frac{2}{3}+\frac{2}{3}-\frac{1}{3}\right) e$ The net charge of a neutron is 0 . This can be got when...

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(a) A conductor A with a cavity as shown in Fig. (a) is given a charge Q. Show that the entire charge must appear on the outer surface of the conductor. (b) Another conductor B with charge q is inserted into the cavity keeping B insulated from A. Show that the total charge on the outside surface of A is Q + q [Fig. (b)]. (c) A sensitive instrument is to be shielded from the strong electrostatic fields in its environment. Suggest a possible way.

Solution: (a) Within the conductor that encloses the hollow, a Gaussian surface is taken into consideration. Within the conductor, the electric field strength (E) will be 0, indicating that it is...

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In a certain region of space, electric field is along the z-direction throughout. The magnitude of electric field is, however, not constant but increases uniformly along the positive z-direction, at the rate of 105 NC–1 per metre. What are the force and torque experienced by a system having a total dipole moment equal to 10–7 cm in the negative z-direction?

Answer: Total dipole moment of the system, p=q×dl=−10−7 cm The rate of increase of the magnitude of the electric field along the positive z-direction = 105 NC–1 per metre. The...

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Careful measurement of the electric field at the surface of a black box indicates that the net outward flux through the surface of the box is 8.0 \times 10^{3} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{C}.
(a) What is the net charge inside the box?
(b) If the net outward flux through the surface of the box were zero, could you conclude that there were no charges inside the box? Why or Why not?

Solutions: (a)Given:  Net outward flux through the surface of the box, $\varphi=8.0 \times 10^{3} \mathrm{~N} \mathrm{~m}^{2} / \mathrm{C}$ Concept: For a body containing net charge $q$, flux...

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Suppose the spheres A and B in Exercise 12 have identical sizes. A third sphere of the same size but uncharged is brought in contact with the first, then brought in contact with the second, and finally removed from both. What is the new force of repulsion between \mathbf{A} and \mathbf{B} ?

Solution: Given: Distance between the spheres, $A$ and $B, r=0.5 \mathrm{~m}$ Initially, the charge on each of sphere $q=6.5 \times 10^{-7} C$ Concept and Calculation: When the sphere is contacted...

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(i) Two insulated charged copper spheres A and B have their centers separated by a distance of 50 \mathrm{~cm}. What is the mutual force of electrostatic repulsion if the charge on each is 6.5 \times 10^{-7} \mathrm{C} each? The radii of \mathbf{A} and \mathrm{B} are negligible compared to the distance of separation.
(ii) What is the force of repulsion if each sphere is charged double the above amount, and the distance between them is halved?

Solution: i) Given: Charge on sphere $\mathrm{A}, q_{A}=6.5 \times 10^{-7} C$ Charge on sphere $\mathrm{B}, q_{B}=6.5 \times 10^{-7} \mathrm{C}$ Distance between the spheres, $r=50 \mathrm{~cm}=0.5...

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Two-point charges qA = 3 µC and qB= –3 µC are located 20 cm apart in a vacuum.
(i) What is the electric field at the midpoint O of the line AB joining the two charges?
(ii) If a negative test charge of magnitude 1.5 × {10^{ - 9}} C is placed at this point, what is the force experienced by the test charge?

i) Given: Charges: qA = 3 µC qB= –3 µC Distance between them = 20 cm Diagrammatic representation of the above question is: Concept: An electric field is a physical field that surrounds...

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