﻿ A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i) , refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly? from Class 10 CBSE Previous Year Board Papers | Science 2012 Solved Board Papers

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# CBSE Class 10 Science Solved Question Paper 2012

#### Multiple Choice Questions

1.

To determine the focal length of a convex lens by obtaining a sharp image of a distant object we generally follow the following steps which are not in proper sequence.

(a) Hold the lens between the object and the screen

(b) Measure the distance between the lens and the screen

(c) Select a well-lit distant object

(d) Place a screen opposite to the object on the lab table

(e) Adjust the position of the lens to form a sharp image

The correct sequence of these steps is:

• c, a, d, e, b

• c, d, a, e, b

•  c, d, e, a, b

•  c, a, e, d, b

B.

c, d, a, e, b

The right sequence of steps is c,d,a,e,b.

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2.

While performing the experiment with raisins to determine the percentage of water absorbed by them, a student made following measurements:

Mass of water in the beaker = 40 g

Mass of raisins before soaking = 5 g

Mass of raisins after soaking for 2 hours = 8 g

Mass of water left in the beaker after the experiment = 35 g

The percentage of water absorbed by raisins is:

D.

The percentage of water absorbed by raisins is calculated by using the formula

where, W2 is the weight of wet resin and W1 is the weight of dry resin.

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3.

A student has to observe a permanent slide of binary fission in amoeba. Find the correct sequence of steps given below for focusing the object under a microscope.

(a) Place the slide on the stage, look through the eye-piece and adjust the mirror to get proper illumination.

(b) Focus the slide sharp using fine adjustment screw

(c) Look through the eye-piece and raise the objective lens using coarse adjustment screw till the object is focused.

(d) Look through the eye-piece and move the slide till the object is visible.

• d, c, b, a

• a, b, d, c

• a, d, c, b

• a, c, d, b

C.

a, d, c, b

The correct order of steps is a, d, c, b.

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4.

While tracing the path of a ray of light passing through a rectangular glass slab a student tabulated his observations as given below:

 S.NO. ∠i ∠r ∠e
•  I 60° 40° 61°
•  II 50o 36o 51o
•  III 40o 28o 39o
•  IV 30o 20o 31o

D.

 IV 30o 20o 31o

The correct option is D.

As per Snell’s law

The ratio of the sine values of i and r should be 1.5.

Note: Refractive index of glass = 1.5 and refractive index of air is 1.

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5.

A student obtained a sharp image of the grills of a window on a screen using a concave mirror. His teacher remarked that for getting better results a well-lit distant object (preferably the sun) should be focused on the screen. What should be done for this purpose?

• Move the screen slightly away from the mirror

• Move the mirror slightly towards the screen

• Move the screen and the mirror away from the object

• Move the screen and the mirror towards the object

B.

Move the mirror slightly towards the screen

When the image distance increases, object distance decreases. Thus, distance between the mirror and screen will decrease. So, the mirror should be moved towards the screen.

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6.

After observing the prepared slides of binary fission in amoeba and budding in yeast following observations were reported:

(a) Single cells of amoeba and yeast were undergoing binary fission and budding respectively.

(B) Cytokinesis was observed in the yeast cell.

(C) Elongated nucleus was dividing to form two daughter nuclei in amoeba.

(D) A chain of buds were observed due to reproduction in amoeba.

The correct observation(s) is/are:

• a and c

• b only

• c and d

• d, a and c

A.

a and c

Both amoeba and yeast are unicellular organisms and undergo asexual reproduction. In Amoeba, a single cell divides to give rise to two identical daughter cells by the process of binary fission. In yeast, the cells reproduce by the process of budding.

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7.

A student after viewing a prepared slide illustrates the budding in yeast in the following order which is not correct:

• b, c, d, e, a

• b, e, d, c, a

• b, d, e, c, a

•  b, d, c, e, a

D.

b, d, c, e, a

During budding in yeast, a single cell develops a protrusion wherein the nucleus divides to give rise to two daughter nuclei. One of the daughter nucleus migrates into the protrusion to form a bud. This bud then enlarges in size and may undergo budding while attached to the parent cell. Hence, budding results in a chain of cells.

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8.

Dry raisins were soaked in water for 2 hours, to determine the percentage of water absorbed by raisins. Before final weighing of swollen raisins, the extra water left on the surface of soaked raisins was removed by:

• gently rubbing with cotton cloth

• hot air blower

•  dry cotton wool

•  filter paper

D.

filter paper

In order to remove the excess water, raisins are dried on a piece of filter paper after being  soaked in water.

1259 Views

9.

To determine focal length of a concave mirror a student obtains the image of a well-lit distant object on a screen. To determine the focal length of the given concave mirror he needs to measure the distance between:

• mirror and the object

• mirror and the screen

• screen and the object

• screen and the object and also mirror and the screen

B.

mirror and the screen

Focal length is the distance between the focus and the mirror. The image of the distant object forms at the focus of the mirror.

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# 10.A student traces the path of a ray of white light through a rectangular glass slab and marks, the angles of incidence (∠i) , refraction (∠r) and emergence (∠e) as shown. Which angle or angles has he not marked correctly? ∠i only ∠i and ∠r ∠i and ∠e ∠r and ∠e

C.

∠i and ∠e

Incident and emergent angles are always  measured from the normal of the plane.

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