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Practice Paper 3

Class X CBSE

Test your preparations !

PRACTICE PAPER -3 

CLASS : X 

SUBJECT: SCIENCE (only PHYSICS question shown here)

(Based on Full Syllabus)

M.M.: 80    DURATION: 3 HRS

GENERAL INSTRUCTIONS:  

(i) All questions are compulsory.

(ii) The question paper has five sections and 12 questions. All questions are compulsory.

(iii) Section–A  has 4 MCQs  and 2 assertion-reason type of 1 mark each; Section–B has 1 questions of  2 marks each; and Section–C  has 3  questions of 3 marks each; Section–D  has 1  questions of 5 marks each; Section–E  has 1 case based question of 4 marks.

(iv) Internal choices have been provided in some questions. A student has to attempt only one of the alternatives in such questions.

(v) For case study questions in section E, there is one choice in one subpart, with 3 questions based per case study.

SECTION  A (MCQs)

Q1    

In the following cases, a ray is incident on a concave mirror. In which case is the angle of incidence equal to zero?

(a) A ray parallel to the principal axis.

(b) A ray passing through the centre of curvature and incident obliquely.

(c) A ray passing through the principal focus and incident obliquely.

(d) A ray incident obliquely to the principal axis, at the pole of the mirror.                                                                                                   

(b) A ray passing through the centre of curvature and incident obliquely.

Q2    

The Unit of potential difference may be expressed as

(a) volt

(b)  Joule / coulomb       

(c) both (a) and (b)

(d) none of the above                                                                                                                                                                                     

(c) both (a) and (b)

Q3    

Two magnetic field lines:

(a) Intersect at neutral point   

(b) Intersect at the midpoint of the magnet       

(c) Intersect near north-pole or south pole         

(d) Never intersect each other            

                                                                                                                                                                                                                 

(d) Never intersect each other 

Q4    

Aditi is advised by his optician to wear spectacles with convex lenses. What type of defect of vision is he suffering from?

(a) myopia           

(b) presbyopia    

(c) hypermetropia     

(d) near-sightedness

                                                                                                                         

(c) hypermetropia 

Q5 to Q6 are assertion-reasoning based questions.

These consist of two statements – Assertion (A) and Reason (R). Answer these questions selecting the appropriate options given below:

(a) Both A and R are true and R is the correct explanation of A.

(b) Both A and R are true but R is not the correct explanation of A.

(c) A is true but R is false.

(d) A is false but R is true.

Q5    

Assertion (A): The near-point of a hypermetropic eye is more than 25 cm away.

Reason (R):  Hypermetropia is corrected using spectacles containing concave lenses.                                                                           

(c) A is true but R is false

Q6    

Assertion (A): The resistivity of a substance does not depend on the nature of the substance and temperature.

Reason (R): The resistivity of a substance is a characteristic property of the material.                             

(d) A is false but R is true

SECTION  B

Q7 to Q7 are very short answer questions

 

Q7   
If the speed of light in vacuum is \( 3\times 10^{8} \;ms^{-1}\), 
find the speed of light in a medium of absolute refractive index 1.5. 
                      OR
A transparent medium A floats on another transparent medium B. 
When a ray of light travels obliquely from medium A to B, the refracted ray 
bends away from the normal. Which of these two media is optically denser and why?                                                        

Given :
\( c= 3\times 10^{8} \;ms^{-1}\)
\( n=1.5\)
\( v=?\)
Using formula
\( n=\frac{c}{v}\)
\(1.5=\frac{3\times 10^{8}}{v}\)
\( v=\frac{3\times 10^{8}}{1.5}=2\times 10^{8}\;ms^{-1}\)

OR

Since the refracted ray bends away from the normal in medium B, it means medium B is a rarer medium. Hence medium A is relatively denser than medium B. The light is travelling from a denser medium to a rarer medium.

SECTION  C

Q8 to Q10 are short answer questions

Q8   
(a) Define the SI unit of potential difference.
(b) What are mA and  \(\mu\) A ?  How are they related to ampere(A) ?
(c) A charge of 20 C passes through a wire which is maintained at a potential difference of 5 V. Calculate the amount of work in moving the charge across the wire ?

(a) SI unit of potential difference is volt (V)
1 volt is the potential difference between two points in an electric circuit if 1 joule of work is done in moving 1 coulomb of charge from one point to the other.
\(1 volt=\frac{1\;joule}{1\;coulomb}\)

(b) \(mA\) stands for milliampere 
\(1mA=10^{-3}\;A\)

\(\mu\) stands for microampere
\(1\mu A=10^{-6}\;A\)

(c) Q = 20 C
V = 5 V
\(W=VQ\)
\(W=50\times20=100\;J\)

Q9   
The image of a candle flame formed by a lens is obtained on a screen placed on the other side of the lens. 
If the image is three times the size of the flame and the distance between lens and image is 80 cm, 
at what distance should the candle be placed from the lens? 
What is the nature of the image and the focal length of the lens?                                                                                                 

\(m=-3\)
\(v=80\)
\(u=\;?\)
using formula of magnification of a lens
\(m=\frac{v}{u}\)
\(-3=\frac{80}{u}\)
\(u=-\frac{80}{3}\)

Using lens formula
\(\frac{1}{f}=\frac{1}{v}-\frac{1}{u}\)
\(\frac{1}{f}=\frac{1}{80}+\frac{3}{80}\)
\(\frac{1}{f}=\frac{4}{80}\)
\(\frac{1}{f}=\frac{1}{20}\)
\(f=20\;cm\)

Nature of image : Real, inverted and enlarged

Q10   
A convex lens of focal length 20 cm can produce a magnified virtual  image. Is this a correct statement? 
If yes, then specify the position of the object and draw a ray diagram to support your answer.
                         OR
An object 5 cm in length is placed 20 cm in front of a convex mirror of radius of curvature 30 cm. 
Find the position, nature and size of the image formed.                                                                                                                    

(a) Yes the statement is correct. A convex lens can produce a magnified virtual image of an object when object is placed between Focus F and optical center O of the lens.

Ray diagram:

OR
\(R=30\;cm\)
\(f=\frac{R}{2}=15\;cm\)
\(u=-20\;cm\)
\( h_{o}=5\;cm\)

Using mirror formula
\(\frac{1}{f}=\frac{1}{u}+\frac{1}{v}\)
\(\frac{1}{15}=\frac{1}{-20}+\frac{1}{v}\)
\(\frac{1}{v}=\frac{1}{15}+\frac{1}{20}\)
\(\frac{1}{v}=\frac{4+3}{60}\)
\(v=\frac{60}{7}=8.57\;cm\)

Size of the image
\(\frac{h_{i}}{h_{o}}=-\frac{v}{u}\)
\({h_{i}}=-\frac{v}{u}\times h_{o}\)
\({h_{i}}=-\frac{60}{7\times(-20)}\times 5=2.14\;cm\)

Nature of image : virtual, erect and diminished

SECTION  D

Q11 to Q11 are long answer questions

Q11  
Explain the refraction of light through a triangular glass prism using a labelled ray diagram. Mark the following in the diagram:
     A – Angle of prism, 
     D – Angle of deviation,  
      i – Incident angle
      r – Angle of refraction,     
      e – Emergent angle
Also label the Incident, Refracted and the Emergent rays
Define the angle of deviation.
 

Diagram:

Angle of deviation : The angle between the directions of the incident ray and the emergent ray is known as angle of deviation.

SECTION  E

Q12 to Q12 are case-based / data-based questions with 2 to 3 short sub-parts.

Internal choice is provided in one of these sub-parts

Q12  

The spherical mirror forms different types of images when the object is placed at different locations. When the image is formed on screen, the image is real and when the image does not form on screen, the image is virtual. When the two reflected rays meet actually, the image is real and when they appear to meet, the image is virtual. A concave mirror always forms a real and inverted image for different positions of the object. But if the object is placed between the focus and pole. the image formed is virtual and erect. A convex mirror always forms a virtual, erect and diminished image. A concave mirror is used as doctor’s head mirror to focus light on body parts like eyes, ears, nose etc., to be examined because it can form erect and magnified image of the object. The convex mirror is used as a rear-view mirror in automobiles because it can form an small and erect image of an object and thus covers a wider field of view. 

 

(a) What is the position of the image when an object is placed at the centre of curvature of a concave mirror? (1)

(b) Why convex mirrors are preferred as a rear-view mirror in automobiles? (1)

(c) A parallel beam of light is allowed to fall on a concave mirror and its sharp image is obtained on a plane sheet of paper.

       (i) What is the name given to the point where the sharp image is obtained?  (1)

      (ii) Determine the radius of curvature, if the point where sharp image is obtained is 10 cm away from the pole of the mirror.  (1)

                                      OR

(c) A linear object of 5 cm size is placed normally at 2F of a concave mirror. What would be the size of its image ? What would be the nature of the image ? (2)

(a) Image is also obtained at C (centre of curvature)
(b) Convex mirror provides a wider field of view as they are curved outwards. It always gives an erect though diminished image.
(c) (i) Focus
(ii) R = 2f = 20 cm

OR
(c) 2F means object is at C (centre of curvature)
Size of the image will be same as the size of the object i.e. 5 cm
Nature of the image - Real and inverted

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