Q19 of 36 Page 1

Read the following and answer any four questions from 19 (i) to 19 (v)

Sumati wanted to see the stars of the night sky. She knows that she needs a telescope to see those distant stars. She finds out that the telescopes, which are made of lenses, are called refracting telescopes and the ones which are made of mirrors are called reflecting telescopes.



So she decided to make a refracting telescope. She bought two lenses, L1 and L2. out of which L1 was bigger and L2 was smaller. The larger lens gathers and bends the light, while the smaller lens magnifies the image. Big, thick lenses are more powerful. So to see far away, she needed a big powerful lens. Unfortunately, she realized that a big lens is very heavy.


Heavy lenses are hard to make and difficult to hold in the right place. Also since the light is passing through the lens, the surface of the lens has to be extremely smooth. Any flaws in the lens will change the image. It would be like looking through a dirty window.


(i) Based on the diagram shown, what kind of lenses would Sumati need to make the telescope?


a) Concave lenses


b) Convex lenses


c) Bifocal lenses


d) Flat lenses


(ii) If the powers of the lenses L1 and L2 are in the ratio of 4:1, what would be the ratio of the focal length of L1 and L2?


a) 4:1


b) 1:4


c) 2:1


d) 1:1


(iii) What is the formula for magnification obtained with a lens?


a) Ratio of height of image to height of object


b) Double the focal length.


c) Inverse of the radius of curvature.


d) Inverse of the object distance.


(iv) Sumati did some preliminary experiment with the lenses and found out that the magnification of the eyepiece (L2) is 3. If in her experiment with L2 she found an image at 24 cm from the lens, at what distance did she put the object?


a) 72 cm


b) 12 cm


c) 8 cm


d) 6 cm


(v) Sumati bought not-so-thick lenses for the telescope and polished them. What advantages, if any, would she have with her choice of lenses?


a) She will not have any advantage as even thicker lenses would give clearer images.


b) Thicker lenses would have made the telescope easier to handle.


c) Not-so-thick lenses would not make the telescope very heavy and also allow a considerable amount of light to pass.


d) Not-so-thick lenses will give her more magnification.


(i)-(b) Convex


The lenses and must be convex. The focal length of the lens is large with a large aperture in order to accommodate maximum light rays coming from the outer-space with a minimum drop in its intensity.


The lens, , is of smaller focal length. It produces an enlarged but sharp virtual image of the distant object i.e. m (magnification is inversely correlated to the focal length; in other words, smaller the focal length, greater will be the size of the image thus obtained)


(ii)-(b) 1:4


Power of a spherical lens is given as



The power of each lens is;


and


It is given, that the ratio of the power of and is 4:1. The focal length of the lenses can be written as



Hence f1/f2=1/4


(iii)-(a) Ratio of the height of the image to the height of the object


The linear magnification of a spherical lens is given as



(iv)-(c) 8 cm


The lateral magnification of a spherical lens is given as



Hence, u = 8 cm


(v)-(c) Not-so-thick lenses would not make the telescope very heavy and they will also allow a considerable amount of light to pass through them.


More from this chapter

All 36 →
17

Read the following and answer any four questions from 17 (i) to 17 (v)

All living cells require energy for various activities. This energy is available by the breakdown of simple carbohydrates either using oxygen or without using oxygen


(i) Energy in the case of higher plants and animals is obtained by


a) Breathing


b) Tissue respiration


c) Organ respiration


d) Digestion of food


(ii) The graph below represents the blood lactic acid concentration of an athlete during a race of 400 m and shows a peak at point D.



Lactic acid production has occurred in the athlete while running in the 400 m race. Which of the following processes explains this event?


a) Aerobic respiration


b) Anaerobic respiration


c) Fermentation


d) Breathing


(iii) Study the graph below that represents the amount of energy supplied with respect to the time while an athlete is running at full speed.




(iv) The characteristic processes observed in anaerobic respiration are


i) presence of oxygen


ii) release of carbon dioxide


iii) release of energy


iv) release of lactic acid


a) i) ,ii) only


b) i), ii), iii) only


c) ii), iii), iv) only


d) iv) only


(v) Study the table below and select the row that has the incorrect information



 18

Read the following and answer any four questions from 18 (i) to 18 (v).

Metallic Character


The ability of an atom to donate electrons and form positive ions (cation) is known as electropositivity or metallic character. Down the group, metallic character increases due to increase in atomic size and across the period, from left to right electropositivity decreases due to decrease in atomic size.


Non-Metallic Character


The ability of an atom to accept electrons to form a negative ion (anion) is called non-metallic character or electronegativity. The elements having high electro-negativity have a higher tendency to gain electrons and form anion. Down the group, electronegativity decreases due to increase in atomic size and across the period, from left to right electronegativity increases due to decrease in atomic size.



(i) Which of the following correctly represents the decreasing order of metallic character of Alkali metals plotted in the graph?


a) Cs>Rb>Li>Na>K


b) K>Rb>Li>Na>Cs


c) Cs>Rb>K>Na>Li


d) Cs>K>Rb>Na>Li


(ii) Hydrogen is placed along with Alkali metals in the modern periodic table though it shows non-metallic character


a) as Hydrogen has one electron & readily loses electron to form negative ion


b) as Hydrogen can easily lose one electron like alkali metals to form positive ion


c) as Hydrogen can gain one electron easily like Halogens to form negative ion


d) as Hydrogen shows the properties of non-metals


(iii) Which of the following has highest electronegativity?


a) F


b) Cl


c) Br


d) I


(iv) Identify the reason for the gradual change in electronegativity in halogens down the group.


a) Electronegativity increases down the group due to decrease in atomic size


b) Electronegativity decreases down the group due to decrease in tendency to lose electrons


c) Electronegativity decreases down the group due to increase in atomic radius/ tendency to gain electron decreases


d) Electronegativity increases down the group due to increase in forces of attractions between nucleus & valence electrons


(v) Which of the following reason correctly justifies that “Fluorine (72pm) has smaller atomic radius than Lithium (152pm)”?


a) F and Li are in the same group. Atomic size increases down the group


b) F and Li are in the same period. Atomic size increases across the period due to increase in number of shells


c) F and Li are in the same group. Atomic size decreases down the group


d) F and Li are in the same period and across the period atomic size/radius decreases from left to right.


 20

Read the following and answer any 4 questions from 20 (i) to 20 (v).

A solenoid is a long helical coil of wire through which a current is run in order to create a magnetic field. The magnetic field of the solenoid is the superposition of the fields due to the current through each coil. It is nearly uniform inside the solenoid and close to zero outside and is similar to the field of a bar magnet having a north pole at one end and a south pole at the other depending upon the direction of current flow. The magnetic field produced in the solenoid is dependent on a few factors such as, the current in the coil, number of turns per unit length etc.


The following graph is obtained by a researcher while doing an experiment to see the variation of the magnetic field with respect to the current in the solenoid.


The unit of magnetic field as given in the graph attached is in milli-Tesla (mT) and the current is given in Ampere.



(i) What type of energy conversion is observed in a linear solenoid?


a. Mechanical to Magnetic


b. Electrical to Magnetic


c. Electrical to Mechanical


d. Magnetic to Mechanical


(ii) What will happen if a soft iron bar is placed inside the solenoid?


a. The bar will be electrocuted resulting in short-circuit.


b. The bar will be magnetised as long as there is current in the circuit.


c. The bar will be magnetised permanently.


d. The bar will not be affected by any means.


(iii) The magnetic field lines produced inside the solenoid are similar to that of …


a. a bar magnet


b. a straight current carrying conductor


c. a circular current carrying loop


d. electromagnet of any shape


(iv) After analysing the graph a student writes the following statements.


I. The magnetic field produced by the solenoid is inversely proportional to the current.


II. The magnetic field produced by the solenoid is directly proportional to the current.


III. The magnetic field produced by the solenoid is directly proportional to square of the current.


IV. The magnetic field produced by the solenoid is independent of the current.


Choose from the following which of the following would be the correct statement(s).


a. Only IV


b. I and III and IV


c. I and II


d. Only II


(v) From the graph deduce which of the following statements is correct.


a. For a current of 0.8A the magnetic field is 13 mT


b. For larger currents, the magnetic field increases non-linearly.


c. For a current of 0.8A the magnetic field is 1.3 mT


d. There is not enough information to find the magnetic field corresponding to 0.8A current


 21

Bile juice does not have any digestive enzyme but still plays a significant role in the process of digestion. Justify the statement.

OR


In birds and mammals the left and right side of the heart are separated. Give reasons.