23 July 2011

CLASS X Important Questions Bank Magnetic effects of electric current

One mark Questions:
Part 1

1. How can you show that the magnetic field produced by a given electric current in the wire decreases as the distance from the wire decreases? 
2. What is the advantage of the third wire of earth connection in domestic appliances? 
3. What constitutes the field of a magnet?
4. What is short-circuiting in an electric supply?
5. What will be the frequency of an alternating current if its direction changes after every 0.01s?
 6. An alternating electric current has a frequency of 50 Hz. How many times does it change its direction in 1s?
7. How is the strength of the magnetic field at a point near a wire related to the strength of the electric current flowing in the wire?
8. How can it be shown that a magnetic field exists around a wire through which a direct current is passing?
9. On what effect of an electric current does an electromagnet work? 
10. What is the direction of magnetic field at the centre of a circular coil carrying current in anticlockwise direction?
Part -2
(Q.1) Passage of current through a straight conductor display some fixed pattern. Pick out the odd one ( 1 mark )
(a) Magnitude of the magnetic field produced at a given point increases as the current through wire increases
(b) The magnetic field produced by a given current in the conductor increases as the distance from it decreases
(c) Direction of the field lines is in accordance with the right hand thumb rule
(d) Field lines are unaffected by the quantity of current flowing.
(Q.2) The phenomenon of electro-magnetic induction is ( 1 mark )
(a) The process of generating magnetic field due to a current passing through a coil.
(b) Producing induced current in a coil due to relative motion between the magnet and the coil.
(c) The process of rotating a coil.  
(d) The process of charging a body. 
(Q.3) A magnetic field cannot exert any force on a( 1 mark )
(a) Moving magnet     (b) Stationary magnet      (c) Stationary charge(d) Moving charge
 (Q.4) Degree of closeness of the magnetic field lines signifies:( 1 mark )
 (a) Number of magnetic fields                                   (b) Distance between different magnetic fields
 (c) Relative strength of the magnetic field                (d) Direction of the magnetic field
(Q.5) What is a magnet? ( 1 mark )
(Q.6) What is the SI unit of induced current? ( 1 mark )
(Q.7) What is the frequency of d.c current? ( 1 mark )
(Q.8) What is the frequency of a.c current that you use in your house? ( 1 mark )
(Q.9) What is magnetic field? ( 1 mark )
(Q.10) There is a battery operated toy, what kind of motor is being used in it? ( 1 mark )
(Q.11) Give two example of devices in which d.c motor is used. ( 1 mark )
(Q.12) Give two examples in which a.c motor is used. ( 1 mark )
(Q.13) What is generator? ( 1 mark )
(Q.14) What is motor? ( 1 mark )
(Q.15) When the current in a wire moves from south to north, the direction of the deflection in the magnetic needle parallel to the wire will be:( 1 mark )
(a) East to west            (b) West to east         (c) East to north              (d) West to south
(Q.16) Magnetic field is a quantity that has both direction and magnitude. Pick out the incorrect statement( 1 mark )
(a) The magnetic field lines emerge from north pole and merge at the south pole.
(b) Inside the magnet, the direction of field lines is from its south pole to its north pole.
(c) Inside the magnet, the direction of field lines is from its north pole to its south pole.
(d) No two field lines intersect each other and the field is strongest where the field lines are crowded.
(Q.17) The region surrounding a magnet, in which the force of the magnet can be detected is said to have( 1 mark )
(a) Magnetic field          (b) Electric field            (c) Magnetic poles           (d) Electric poles
(Q.18) Which of the following is not the special features of magnets? ( 1 mark )
(a) They align in the North –South direction when suspended freely.
(b) They have two distinct North and South poles.
(c) Like poles attract each other and unlike poles repel each other.
(d) The magnetic field lines produced due to a magnet are closed curves.
(Q.19) Direction of the force experienced by a current-carrying conductor when placed in a magnetic field is dependent on ( 1 mark )
(a) Direction of the current alone            
(b) Direction of the magnetic field alone
(c) Direction of current as well as the direction of magnetic field
(d) Direction of electric field
(Q.20) The magnitude of the force experienced by a current-carrying conductor when placed in a magnetic field will be( 1 mark )
(a) Maximum if the directions of current and magnetic field are perpendicular to each other
 (b) Minimum if the directions of current and magnetic field are perpendicular to each other
 (c) Maximum if the directions of current and magnetic field are opposite to each other (d) Maximum if the directions of current and magnetic field are same
(Q.21) Which of the following is not true for an electric generator( 1 mark )
(a) Converts mechanical energy into electrical energy.
(b) Works on the basis of electromagnetic induction.
(c) Can be used to generate AC or DC.
(d) Converts electrical energy to mechanical energy
(Q.22) An alpha particle is projected towards west and gets deflected towards north by a magnetic field. The direction of the magnetic field is ( 1 mark ) 
(a) Towards south                   (b) Towards east             (c) Downwards            (d) Upwards
(Q.23) An electric current through a metallic conductor produces a/an _________ around it. ( 1 mark )
(a) Electric field          (b) Magnetic field            (c) Electromagnetic effect. (d) Gravitational field
(Q.24) A straight conducting wire is placed parallel to and over a compass needle. The deflection in the needle ( 1 mark )
(a) Becomes opposite when the direction of the current is reversed
(b) Remains in the same direction even on reversing the direction of current
(c) Keeps fluctuating on passage of current in any direction
(d) Is negligible on reversing the direction of current
(Q.25) At every point of a current carrying circular loop, the concentric circles representing the magnetic fields around it would become( 1 mark )
(a) Larger and larger as we move away from the wire.
(b) So large at the centre of circular loop that they look like straight lines.
(c) Smaller and smaller as we go away from the wire.
(d) There is no fixed pattern for circles
(Q.26) Which of the following statements is not true?( 1 mark )
(a) The pattern of the magnetic field around a conductor due to an electric current flowing through it depends on the shape of the conductor.
(b) The magnetic field of a solenoid carrying a current is similar to that of a bar magnet.
(c) Magnitude of magnetic field is directly proportional to the quantity of current flowing through the current.
(d) Magnetic field produced by the passage of current through a straight wire is permanent.
(Q.27) Magnetic field produced inside a solenoid are so strong that ( 1 mark )
(a) They can be used to magnetize a magnetic material, when placed inside the coil.
(b) They can be used to magnetize a magnetic material, when placed near the coil.
(c) They are still not able to magnetize a magnetic material. (d) They become permanent.
(Q.28) Increase in number of turns of a coil in the solenoid will( 1 mark )
(a) Have no effect on the strength of magnetic field   (b) Will add to the strength of the magnetic field
 (c) Will decrease the strength of the magnetic field    (d) Will change the direction of the magnetic field
(Q.29) An electromagnet consists of a core of ___________ wrapped around with a coil of ________ copper wire.( 1 mark )
(a) Soft iron, insulated     (b) Aluminum, Insulated     (c) Soft iron, uncovered (d) Magnet, uncovered
(Q.30) A current-carrying conductor when placed in a magnetic field experiences ( 1 mark ) 
(a) An acceleration   (b) A force          (c) Demagnetization    (d) It always remains in equilibrium
(Q.31) An electric motor is a device( 1 mark )
(a) That converts electrical energy into kinetic energy
(b) That converts electrical energy to mechanical energy
(c) There is no energy conversion of one form to another.
(d) That converts sound energy to light energy.
(Q.32) Which of the following statements cannot be related to the construction of an electric motor? ( 1 mark )
(a) A rectangular coil of insulated copper wire is placed between the two poles of a magnetic field such that two of its parallel sides are perpendicular to the direction of the magnetic field.
(b) The ends of the coil are connected to the two halves of a split ring.
(c) The inner insulated sides are attached to axle whereas the external conducting edges touch two conducting stationary brushes.
(d) The coil and the axle continuously rotate in one direction.
(Q.33) The direction of the induced current is given by( 1 mark )
(a) Right Hand Thumb Rule
 (b) Fleming’s Left Hand Rule
(c) Fleming’s Right hand Rule
(d) Faraday's law
(Q.34) According to Fleming’s Right Hand Rule, if we stretch the thumb, forefinger and middle finger of right hand – forefinger indicates direction of magnetic field, thumb shows the direction of motion of conductor, and then the middle finger will show the direction of ( 1 mark )
(a) Induced current        (b) Magnetic Force    (c) Alternating Current   (d) Electric force
(Q.35) The induced current is highest when ( 1 mark )
(a) Direction of motion of coil is at 900 to the magnetic field.
(b) Direction of motion of coil is at 300 to the magnetic field.
(c) Direction of motion of coil is at 600 to the magnetic field.
(d) Direction of motion of coil is at 1800 to the magnetic field.
(Q.36) Parameters of electricity supply in India are ( 1 mark )
(a) Potential Difference of 220 V, Frequency of 50 hertz and Current Rating of 5A/15A
(b) Potential Difference of 150 V, Frequency of 40 hertz and Current Rating of 10 A
(c) Potential Difference of 220 V, Frequency of 60 hertz and Current Rating of 15A
(d) Potential Difference of 220 V, Frequency of 40 hertz and Current Rating of 5 A
(Q.37) Pick the incorrect statement regarding fuse. Fuse is used for protecting the circuits due to ( 1 mark )
(a) Short-circuiting   (b) Overloading of circuits   (c) Faulty connections  (d) Theft
(Q.38) Which of the following will not cause overloading? ( 1 mark )
(a) Accidental hike in the supply voltage  b) Connecting many appliances to a single socket
 (c) Melting of fuse     (d) Short circuiting
Two marks Questions: 1. With the help of a neat-diagram, describe how you can generate induced current in a circuit.
2. What is meant by the term “Magnetic field Lines”? List two properties of magnetic field lines.
3. Write the rule which determines the direction of magnetic field developed around a straight
conductor when current is passed through the conductor.
4. State the rule to determine the direction of magnetic field produced around a current carrying
conductor.
5. On which factors does the force experienced by a current carrying conductor placed in a uniform
magnetic field depend?
6. State Fleming’s right-hand Rule.
7. Why is series arrangement not used for domestic circuits?
8. Differentiate between electric force and magnetic forces.
9. How does AC differ from DC? What are the advantages and disadvantages of AC over DC?
10. Draw the magnetic field due to a current carrying circular coil. State the clock rule to find the
polarities of the faces of the coil.
11. What will be the frequency of an alternating current, if its direction changes after every 0.05 sec?
12.What is the principle on which working of electric generator is based? What are its important part?.
13.Why two magnetic lines of forces don’t intersect each other?
14. Give two methods with which we can increase the strength of magnetic field produced by a circular coil carrying current?
Three Mark Questions 
1. Draw the pattern of field lined due to a solenoid carrying electric current. Mark the north and the south poles in the diagram.
2. Draw the pattern of lines of force due to a magnetic field through and around a current carrying loop of wire. How would the strength of the magnetic field produced at the centre of the circular loop be affected if 
(i) the strength of the current passing through this loop is doubled? 
(ii) the radius of the loop  is reduced to half of the original radius?
3. Draw the pattern lines of force due to a magnetic field associated with a current carrying conductor. State how the magnetic field produced changes 
(i) with an increase in current in the conductor and
(ii) the distance from the conductor.
4. Draw the pattern of field lines due to a bar magnet. Mention any two properties of the magnetic field  lines. 
5. How does the strength of the magnetic field at the centre of a circular coil of wire depend on:
 (i) the radius of the coil? 
(ii) the number of turns of the wire? 
(iii) the strength of the current flowing in the coil?
6. The flow of a current in a circular loop of a wire creates a magnetic field at its centre. How can
existence of the field be detected? State the rule which helps to predict the direction of this magnetic
field.
7. What are the factors on which the strength of magnetic field produced by current-carrying solenoid
depends?
8. A coil of copper wire is connected to a galvanometer. What would happen if a bar magnet is: 
(i) pushed into the coil with north pole entering first 
(ii) pulled out of the coil 
(iii) held stationary inside the coil?
9. Explain what is short-circuiting and overloading in an electric supply.
10. What are magnetic field lines? How is the direction of a magnetic field at a point determined?
11.What are the factors which govern the force experienced by a current carrying conductor placed in a uniform magnetic field depends? ( 3 Marks )
12. Distinguish between an electric motor and generator?
13.What is direct current (d.c) and alternating current (a.c).
14.A current of 2 A flows through a circular coil of radius of 4 cm, and has 10 turns. The coil is
aligned horizontally and current flows though the coil in clockwise direction. Find the magnitude and
direction of magnetic field at the centre of the coil due to the current.
Five Mark Questions:
1. (a) Suggest an activity to show the pattern of magnetic field lines, when you are provided with a bar magnet, a cardboard piece and iron filings
(b)Draw a rough sketch of the field lines which you will observe.
2. (a) What is an electromagnet? What does it consists of? 
(b) Name one material in each case used to make a
 (i) permanent magnet (ii) temporary magnet. 
(c) Describe an activity to show how can you make an electromagnet in your school lab?
3. State Fleming’s left-hand rule. With a labeled diagram, describe the working of an electric motor. What is the function of split-ring Commutator in a motor?
4. State Fleming’s right-hand rule. With a labeled diagram, describe the working of an AC electric generator.
5. Draw the lines of force of the magnetic field through and around (a)single loop of wire carrying current, (b) a solenoid carrying electric current.
6. Why is pure iron not used for making permanent magnets? Name one material used for making permanent magnets. Describe how permanent magnets are made electrically. State two examples of electrical appliances made by using permanent magnets.
7. (a)Draw a schematic labeled diagram of a domestic wiring circuit which includes (i)a main fuse (ii) a power meter (iii)one light point (iv) a power plug.(b) Why is it necessary to connect an earth wire to electric appliances having metallic covers?
8. (a)What are magnetic field lines? How is the direction of a magnetic field at a point determined? (b) Draw two field lines around a bar magnet along its length on its two sides and mark the field directions on them by arrow marks. (c) List any three properties of magnetic field lines.
9. What is an electric motor? With the help of a diagram, describe the working of an electric motor.
10. What are magnetic field lines? Write their characteristics. Draw the magnetic field lines due to a current flowing in a circular coil.
11. Explain the principle, construction and working of an electric motor.
12. Explain with labeled diagram, the principle, construction and working of an electric generator.
13. (a ). What is an electromagnet ?    (b). List any of its two uses.
(c ). Draw a labeled diagram to show how an electromagnet is made.
(d ). What is the purpose of the soft iron core used in making an electromagnet ?
14.A solenoid is 1 m long and 2 cm in diameter has 50 turns/cm. A current of 5 A is flowing through it. Calculate the magnetic induction:    a) Inside the solenoid.   b) At one end on the axis of solenoid.
15. Explain the construction and working of electric motor?
16. What is the principle behind the working of electric generator? Explain its working with the help of well labeled diagram.
17. The mains power supply of a house is through a 5-A fuse. How many 100-W bulbs can be used in this house at the correct voltage?
18. A wire 10 cm long and carrying a current of 1.5 A is held in a uniform magnetic field in which B=10-3 T. Calculate the force on the wire if it is held perpendicular to the lines of the magnetic field.
19 A current of 10 A flows in a circular coil of 1000 turns and radius 0.1 m. Find the magnitude of the magnetic field at the centre of the coil.
20. At what distance from a straight conductor carrying a current of 2.8 A, will the magnetic induction be 2.8×10-5 T?
21. Find the strength of the current which will produce a magnetic field of 10-4 T at the centre of a coil of mean radius 0.10 m. The coil comprises 20 turns.
22. A 0.4 m wire, stretched horizontally, carries an electric current of 15 A from East to West, in a magnetic field whose magnetic field intensity is 0.1 N/Am, directed vertically downwards. What is (a) the magnitude of the magnetic deflecting force on the wire, and (b) its direction?

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