Friday, July 27, 2012

CBSE PHYSICS: X Magnetic effect of current CBSE Test paper solved

                               CBSE TEST PAPER -2012-13
 Time: 1hr.  CHAPTER: MAGNETIC EFFECT OF CURRENT        FM: 30
1. A positively charged particle (alpha-particle) projected towards west is deflected towards north by magnetic field. The direction of magnetic field is          
(a) towards south (b) towards east (c) downward (d) upward.
2. A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each   
(a) two revolutions (b) one revolution (c) half revolution (d) one-fourth revolution.
3. Permanent magnets are made up of
(a) Alnico     (b) soft iron  (c) copper (d) aluminum.                            
4. Which of the following properties of a proton can change when it moves freely in a magnetic field
(a) Mass              (b) speed              (c) velocity           (d) momentum
5. The direction of the magnetic field at a point P above the wire carrying current is
(a) Down the page (b) up the page  (c) into the page   (d) out of the page
6. An alternating current has frequency of 50 Hz. How many times does it change its direction in one second?
7 . What is the advantage of the third wire of earth connection in domestic appliances?
8.  What is the S.I. unit of magnetic flux ?
Ans:  Weber : The magnetic flux linked with a surface is defined as the number of magnetic field lines passing normally through that surface.
9 . How can we increase the speed of a D.C. motor?
10. Why do not two magnetic field lines intersect each other?
11. What is a solenoid? Draw magnetic field lines showing the magnetic field inside and outside the current carrying solenoid?
12. (a) What is short circuiting? (b) What is overloading? How can you avoid overloading?
13. What are the ways to detect the polarity of a current carrying solenoid?
14. Consider a circular loop of wire lying in the plane of the table. let the current pass through the loop clockwise. Apply the right hand rule to find out the direction of magnetic field inside and outside the loop?
15. What is the orientation of a current caring conductor relative to the direction of magnetic field for
(a) Maximum magnetic force.              (b) Minimum magnetic force
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                     CBSE TEST PAPER -2012-13 Answers
 Time: 1hr.  CHAPTER: MAGNETIC EFFECT OF CURRENT             FM: 30
1.  Ans. (a) Toward south.
2. (c) half revolution
3.(a) Alnico     (b) soft iron  (c) copper (d) aluminum.                            
4.(c) velocity             
5.(d) out of the page
6. Ans.  As the frequency is 50 Hz, so a.c. completes 50 cycles in 1 second. In other words, it reverses its direction 100 times in one second.
7.Ans: Earth wire is connected to the metallic case of an electrical appliance to  protect from electric shock by transferring excess amount of current to the earth.
8. Ans:  Weber : The magnetic flux linked with a surface is defined as the number of magnetic field lines passing normally through that surface.
9 .  Ans. We can increase the speed of rotation of a D.C.  motor by increasing
(i) area of the coil   (ii) number of turns in the coil   (iii) magnetic field and (iv) current.
10.  Ans: The two magnetic field lines never intersect each other because at the point of intersection there will be two directions of magnetic field, which is not possible
11.  Ans: A coil of many turns of insulated copper wire closely wound in the shape of a ring is known as a solenoid.
12.  Ans(a) when live wire and the neutral wires come in contact with each other resistance of the circuit becomes very small and huge amount of current flows and produces large heat which can cause fire. This phenomenon is called short circuiting
(b). If  many electrical appliances of high power ratings are connected in a single socket large amount of current  starts flowing in the circuit. This phenomenon is called overloading.
It can be avoided by the following methods
(i) Not use too many appliance is a single socket
(ii) To apply preventive methods of short circuiting.

13. Ans: If the current in the coil facing you is flowing in clockwise direction then its the south pole. If the current is flowing in anti clockwise direction, then its the north pole.
14. Ans: Inside the loop, direction of the magnetic field lines are into the table.
Outside the loop the magnetic field lines are coming out of the table.
15.  Ans: (a) The maximum force is exerted on a current carrying conductor only when it is perpendicular to the direction of magnetic field.
(b)The minimum force or can say no force acts on a current carrying conductor when it is parallel to the magnetic field.
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