Please refer to Chapter 13 Magnetic Effect of Electric Current Processes Class 10 Science Important Questions with solutions provided below. These questions and answers have been provided for Class 10 Science based on the latest syllabus and examination guidelines issued by CBSE, NCERT, and KVS. Students should learn these problem solutions as it will help them to gain more marks in examinations. We have provided Important Questions for Class 10 Science for all chapters in your book. These Board exam questions have been designed by expert teachers of Standard 10.
Class 10 Science Important Questions Magnetic Effect of Electric Current Chapter 13
Very short answer type Questions :
Question. How is magnetic field produced in a solenoid used?
Answer: It is used to magnetise a soft iron bar to form an electromagnet.
Question. How is induced current in a secondary coil related to the current flowing in the primary coil?
Answer: It may be greater than or less than primary coil.
Question. In the arrangement shown in figure there are two coils wound on a nonconducting cylindrical rod.
Initially the key is not inserted in the circuit. Later the key is inserted and then removed shortly after.
What are the two observations that can be noted from the galvanometer reading?
Answer: There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions.
Question. What does the direction of thumb indicate in the right hand thumb rule?
Answer: The thumb indicates the direction of current in the straight conductor held by curved fingers of our hand.
Question. Suggest one way to distinguish a wire carrying current from a wire carrying no current.
Answer: The magnetic compass needle will get deflected near the wire current carrying but not near the wire with no current.
Question. Why are magnetic field lines form closed curves?
Answer: It is because outside the magnet, magnetic field lines start from north pole and merge at south pole whereas inside the magnet they start from south pole and merge at north pole, therefore these lines from closed curves.
Question. Why don’t two magnetic lines of force intersect each other?
Answer: No two magnetic field lines intersect each other because if they did, it would mean that at the point of intersection, the compass needle would point towards two direction, which is not possible.
Question. Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer: The direction is vertically downwards.
Question. When a magnet is moved into the coil of wire as shown in the figure, there is small reading in the ammeter. How can we increase the reading?
Answer: It can be done by pushing the magnet or coil faster towards, respectively the magnet or coil.
Question. Name any one method to induce current in a coil.
Answer: It can be done by moving a magnet towards the coil.
Question. What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?
Answer: It indicates that strength of magnetic field decreases near the end of the solenoid.
Question. What is the role of the two conducting stationary brushes in a simple electric motor?
Answer: They make the contact between the two halves of the split rings and the battery. Current from the battery enters a conducting brush and flows back to the battery through the brush.
Question. State Faraday’s first law of electromagnetic induction.
Answer: When magnetic field in around a conducting coil is changed, induced emf is produced.
Question. A square coil moves in a plane with uniform velocity ‘V’ parallel to its sides and magnetic field acts at 90° into the loop. What is the induced current in the coil?
Answer: Zero, it is because there is no change in magnetic flux.
Question. A current through a horizontal power line flows from east to west direction. What is the direction of magnetic field at a point directly below it and at a point directly above it?
Answer: At a point below it, the direction is from North to South and at a point above it, the direction is from South to North.
Question4. If in a straight wire ‘A’, current is flowing in vertically downward direction whereas in the straight wire ‘B’ current is flowing in vertically upward direction. What is the direction of magnetic field (a) in wire ‘A’, (b) in wire ‘B’.?
Answer: (a) Anticlockwise, (b) Clockwise
Question. State Faraday’s second law of electromagnetic induction.
Answer: The induced e.m.f depends directly upon the relative speed between the coil and the magnet.
Question. What is the principle of an electric motor?
Answer: It is based on the principle that a force is experienced by the current carrying conductor in a magnetic field. The two forces on the opposite sides of current carrying rectangular coil in a magnetic field will act in different lines, thus bringing the rotational motion.
Question. Meena draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the centre of the circular loop, she observes that the lines keep on diverging. How will you explain her observation?
Answer: Strength of magnetic field decreases with increase in distance from the from the magnetic substance.
That is why magnetic lines keep on diverging due to decrease in magnetic field.
Short Answer: I
Question. You are given three identical looking bars one of which is a magnet, the other made of a magnetic material and the third made of a non magnetic material. Using just these three bars how will you find out which is which?
Answer: Bring one bar close to the other two one by one: if the bar attracts one of these and does not attract the other one, the bar which is not attracted is made of non-magnetic material and the bar in our hand is a magnet or a bar of magnetic material. Keep one bar on the table and move other bar along its length from one end to the other, if uniform attraction is felt the bar in our hand is a magnet and vice versa.
Question. State the condition for electromagnetic induction to take place. A cylindrical bar magnet is kept along the axis of circular coil as shown in the figure. Will there be a current induced in the coil, if the magnet is rotated about its axis? Discuss.
Answer: • Either the coil or the magnet should be in motion
• If there is relative motion between a coil carrying current and coil not carrying current, there will be induced current in the second coil.
• No current will be induced because there is no change in magnetic field which is essential to produce induced current.
Question. What is the role of split rings in an electric motor?
Answer: It act as a commutator in D.C (direct current) motor. The direction of current through the coil is reversed with the help of split rings after every half rotation of the coil, direction of current in the rotating coil remains the same and the coil continues to rotate in the same direction, thus producing direct current.
Question. Describe an activity to show magnetic field lines are produced when current is passed through circular coil.
Answer: (i) Take a rectangular cardboard having two holes.
(ii) Insert a circular coil through these holes, normal to the plane of paper.
(iii) Connect the ends of coil in series with a battery, and key.
(iv) Sprinkle iron filings uniformly on the cardboard.
(v) Plug the key.
(vi) Tap the cardboard gently a few times. Note the pattern of the iron filings.
(vii) The pattern of magnetic field lines will be same as the pattern of iron filings.
Question. What are magnetic field lines? How is the direction of magnetic field at a point deter- mined?
Answer: (i) The magnetic field lines produced is into the plane of the paper at R and out of it at S.
(ii) Field at S > Field at P
Magnetic field strength for a straight current carrying conductor is inversely proportional to the distance from the wire.
(iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now in the clockwise direction on the plane which is perpendicular to the wire carrying current.
(iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in which the fingers are wrapped around the wire will give the direction of the magnetic field.
Question. (a) Mention the factors on which the direction of force experienced by a current carrying conductor placed in a magnetic field will depend.
(b) Under what conditions is the force experienced by a current carrying conductor placed in a magnetic field maximum?
(c) A proton beam is moving along the direction of a magnetic field. What force is acting on proton beam?
Answer: (a) (i) direction of current, (ii) direction of magnetic field.
(b) When direction of current is perpendicular to the direction of magnetic field, the force experienced will be maximum.
(c) No, force is exerted by a proton beam because proton beam is moving along the direction of magnetic field.
Question. Distinguish between a bar magnet and an electromagnet.
Answer:
Question. Write one application for each of the following:
(a) Right-hand Thumb Rule,
(b) Fleming’s left Hand Rule,
(c) Fleming’s Right Hand Rule.
Answer: (a) It is used to find the direction of magnetic field in a coil of wire and electric current in a straight conductor.
(b) It is used to find the direction of force exerted on a current carrying conductor in a magnetic field.
(c) It is used to find the direction of induced current in a closed circuit placed in a changing magnetic field, e.g. in an electric generator.
Question. List three sources of magnetic field.
Answer: (i) Magnetic field is associated with bar magnet
(ii) A current carrying conductor produces magnetic field.
(iii) A current carrying curricular loop also produces magnetic field.
Question. When a magnet was pushed towards a solenoid, the galvanometer connected to the solenoid showed a deflection in right direction. When the same magnet was pulled away from the solenoid at a faster speed, what was the deflection in the galvanometer?
Answer: Deflection in galvanometer will be towards the left, because when the direction of movement of magnet is reversed, the direction of induced current is also reversed. The induced current is increased but it is flowing in opposite direction when the magnet is moving faster and in opposite direction.
Question. What is meant by electromagnetic induction? State the rule which helps to determine the direction of induced current.
Answer: It is the phenomena of production of induced current and potential difference in a conductor by moving a magnet or if there is a change in magnetic field or flux.
Fleming’s right hand rule for determining the direction of induced current: Hold the thumb, the forefinger and central finger of your right hand perpendicular to each other in such a way that forefinger represents the direction of magnetic field, the thumb points in the direction of motion of conductor, then the central finger will give the direction of induced current in the conductor.
Question. Explain different ways to induce current in a coil.
Answer: (i) By changing the direction of current in the conductor.
(ii) By changing the magnetic field in around the coil.
Question. Imagine that you are sitting in a chamber with your back to one wall. An electron beam moves horizontally from back wall towards the front wall and by a strong magnetic field to your right side.
What is the direction of magnetic field?
Answer:
Current will move in the opposite direction to the flow of electrons. The direction of magnetic field will be downwards as shown in the figure.
Question. An alpha particle (positively charged) enters a magnetic field at right angle to it as shown in figure. Explain with the help of relevant rule, the direction of force acting on the alpha particle.
Answer: The force will act in upward direction given by thumb, if forefinger points in the direction of magnetic field and the middle finger points in the direction of current, according to Fleming’s left hand rule.
Question. What is meant of solenoid? How does a current carrying solenoid behave? Give its main use.
Answer: The long coil containing large number of close turns of insulated copper wires wrapped around, is called a solenoid.
Current carrying solenoid behaves like a bar magnet. It is called an electromagnet.
It is used for making electromagnets.
Question. With the help of diagram of experimental set up describe an activity to show that the force acting on a current carrying conductor placed on magnetic field increases with increase in field strength.
Answer: (i) Take an aluminium rod, AB of size 3 inches.
(ii) Suspend it horizontally using connecting wires
(iii) Place a horse-shoe magnet in such a way that the rod lies between the two poles with magnetic field directed upwards.
(iv) Put north pole of the magnet vertically below and south pole vertically above the rod.
(v) Connect aluminium rod in series with the battery and key.
(vi) Now pass the current in the rod from B to A.
(vii) Aluminium rod will be displaced towards the left.
(viii) Now bring a stronger horse-shoe magnet and observe the displacement of rod.
(ix) The displacement of rod will increase with the increase in strength of the magnetic field.
Question. Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will the same current be induced in the coil B? Give reason.
Answer: No, the induced current in coil ‘B’ will change. It is because magnetic field produced in coil ‘A’ will change, therefore magnetic field induced in coil ‘B’ will also change. Hence induced current in the coil will also change.
Question. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a) pushed into the coil, (b) withdrawn from inside the coil, (c) held stationary inside the coil?
Answer: (a) It will show deflection.
(b) The deflection will be in the opposite direction.
(c) The galvanometer will not show any deflection.
Question. A magnetic compass needle is placed in the plane of paper near point A as shown in the figure. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what conditions is the deflection maximum and why?
Answer: Straight current carrying conductor should be placed in the plane of paper. The magnetic field produced will be at 90° to the plane of paper and parallel to the vertical axis of magnetic needle. The deflection will be maximum when current carrying conductor is at 90°to the plane of paper and magnetic field will be in the direction parallel to the plane of paper.
Question. Under what conditions a permanent electromagnet is obtained if a current carrying solenoid is used?
Support your answer with the help of a labeled circuit diagram.
Answer: (i) Direct current should be used.
(ii) Magnitude of current should be large.
(iii) The number of turns in solenoid are more and close to each other
like windings in an electric motor.
(iv) The soft core inside the solenoid should be made up of steel.
Question. It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles,
(ii) neutrons? Justify your answer.
Answer: (i) Yes, similar magnetic fields are produced. α-particles are positively charged particles, so current will be in the direction of motion of beam of particles.
(ii) No, in neutrons no current will be produced, as these are neutral particles.
Question. Figure shows equipments used to demonstrate electromagnetic induction.
Two pieces of soft iron core ‘A’ and ‘B’ each having a coil of insulated wire wrapped around them. The coil around ‘A’ is connected to a switch and a cell. The coil around ‘B’ is connected to a galvanometer. When the switch is closed, the galvanometer shows a rapid deflection to the left before returning to zero.
(i) Explain why the galvanometer shows a rapid deflection to the left before returning to zero?
(ii) Explain what, if anything, would be observed on the galvanometer as the switch is opened?
Answer: (i) When the switch is closed, a changing magnetic field is produced in A which produces a change in magnetic field in ‘B’ resulting in induced current. However, the magnetic field in A becomes steady after sometime. Therefore, there is no more induced current in B as there is no change in the magnetic flux and the reading is zero.
(ii) When the switch is opened, there is deflection in the galvanometer but in the opposite direction.
The decreasing magnetic field in A produces an induced current in B. Since the change is reversed,
the direction of induced current is also reversed.
Question: When a magnet is moved into the coil of wire as shown in the figure, there is small reading in the ammeter. How can we increase the reading?
Answer.It can be done by pushing the magnet or coil faster towards, respectively the magnet or coil.
Question: What is the principle of an electric motor?
Answer.It is based on the principle that a force is experienced by the current carrying conductor in a magnetic field. The two forces on the opposite sides of current carrying rectangular coil in a magnetic field will act in different lines, thus bringing the rotational motion.
Question: Meena draws magnetic field lines of field close to the axis of a current carrying circular loop. As she moves away from the centre of the circular loop, she observes that the lines keep on diverging. How will you explain her observation?
Answer.Strength of magnetic field decreases with increase in distance from the from the magnetic substance.That is why magnetic lines keep on diverging due to decrease in magnetic field.
Question. What is a solenoid? Draw the pattern of magnetic field lines of a solenoid through which a steady current flows. What does the pattern of field lines inside the solenoid indicate?
Answer: Solenoid : A coil of many circular turns of insulated copper wire wrapped in the shape of The pattern of magnetic field lines inside the solenoid indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.cylinder is called solenoid.
Question. A charged particle enters at right angle into a uniform magnetic field as shown. What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field?
Answer: By using Fleming’s left hand rule if the direction of motion of charged particle to be vertically out of the page, then the charged particle must be positive in nature.
Question. When is the forces experienced by a current carrying conductor placed in a magnetic field the largest?
Answer: Force experienced by a current carrying conductor placed in a magnetic field is largest when the direction of current is perpendicular to the direction of magnetic field.
Question. Draw a diagram to show the magnetic field lines around a current carrying solenoid?
What do you interpret from the pattern of the field lines?
Answer:
From the pattern of magnetic field lines due to a current carrying solenoid, we conclude that its pattern is similar to the pattern of magnetic field lines due to a bar magnet. One end of the solenoid behaves as a magnetic north pole, while other behave as the south pole.
Question. (a) Distinguish between the terms ‘overloading’ and ‘short-circuiting’ as used in domestic circuits.
(b) Why are the coils of electric toasters made of an alloy rather than a pure metal?
Answer: (a) Overloading is a situation in which there is sudden hike of current in the domestic circuit which may be caused by connecting too many appliances into one socket.
Short circuiting is a situation in which the live wire comes in contact directly with neutral wire. Short circuiting can leads to overloading.
(b) Coils of electric toasters are made of an alloy rather than a pure metal because the resitivity value of alloy is greater than that of the pure metal.
Greater the resistivity of a material, more will be the heat produced.
Question. Draw a diagram to show the magnetic field lines around a bar magnet. List any two properties of magnetic field lines.
Answer:
(i) Magnetic field lines start from the north pole of a magnet and end at the south pole of a magnet.
(ii) Two magnetic field lines can not intersect each other.
Question. A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is
(i) moved quickly towards it,
(ii) moved quickly away from the coil and
(iii) placed near its one face Name the phenomena involved.
Answer: If a coil of insulated wire is connected to a galvanometer and a bar magnet with north pole is moved towards one face of the coil then, given situation is shown in the figure.
(i) Moved quickly towards the coil : A current is induced in anti-clockwise direction in the coil with respect to the side facing the north pole of the magnet and needle of galvanometer will deffect in one direction from zero position.
(ii) Moved quickly away from coil : A current is induced in clockwise direction in the coil with respect to the side facing the north pole of the magnet and the needle of the galvanometer will deffect in opposite direction from (i).
(iii) Placed near its one face : No deflection of the needle of galvanometer is observed.
The phenomena involved is called electromagnetic induction.
Question. What is meant by the term, “magnetic field”?
Why does a compass needle show deflection when brought near a bar magnet?
Answer: Magnetic field : It is defined as the space surrounded the magnet in which magnetic force can be experienced.
Compass needle is itself made up of tiny magnet.
When it is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet.
Hence needle shows defiection.
Question. (a) Draw a schematic labelled diagram of a domestic wiring circuit which includes
(i) a main fuse
(ii) a power meter
(iii) one light point
(iv) a power output socket
(b) In this circuit, on which wire of the circuit is the mains on/of switch connected?
Answer: (a)
(b) As shown in this circuits, mains on of switch is connected with live wire and neutral wire.
Question. State the rule which gives the direction of magnetic field associated with a currentcarrying conductor.
Answer: Maxwell’s right hand thumb rule or corkscrew rule gives the direction of magnetic field associated with a current carrying conductor.
Question: What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?
Answer.It indicates that strength of magnetic field decreases near the end of the solenoid.
Question: What is the role of the two conducting stationary brushes in a simple electric motor?
Answer.They make the contact between the two halves of the split rings and the battery. Current from the battery enters a conducting brush and flows back to the battery through the brush.
Question: State Faraday’s first law of electromagnetic induction.
Answer.When magnetic field in around a conducting coil is changed, induced emf is produced.
Question: A square coil moves in a plane with uniform velocity ‘V’ parallel to its sides and magnetic field acts at 90°° into the loop. What is the induced current in the coil?
Answer.Zero, it is because there is no change in magnetic flux.
Question: How is induced current in a secondary coil related to the current flowing in the primary coil?
Answer.It may be greater than or less than primary coil.
Question: Name any one method to induce current in a coil.
Answer.It can be done by moving a magnet towards the coil.
Question: State Faraday’s second law of electromagnetic induction.
Answer.The induced e.m.f depends directly upon the relative speed between the coil and the magnet.
Question: In the arrangement shown in figure there are two coils wound on a nonconducting cylindrical rod.Initially the key is not inserted in the circuit. Later the key is inserted and then removed shortly after.
What are the two observations that can be noted from the galvanometer reading?
Answer.There are momentary galvanometer deflections that die out shortly; the deflections are in opposite directions.
Question: Draw a diagram to show the magnetic field lines around a current carrying solenoid? What do you interpret from the pattern of the field lines?
Answer:
From the pattern of magnetic field lines due to a current carrying solenoid, we conclude that its pattern is similar to the pattern of magnetic field lines due to a bar magnet. One end of the solenoid behaves as a magnetic north pole, while other behave as the south pole.
Question: A coil of insulated wire is connected to a galvanometer. What would be seen if a bar magnet with its north pole towards one face of the coil is
(i) moved quickly towards it,
(ii) moved quickly away from the coil and
(iii) placed near its one face
Name the phenomena involved.
Answer: If a coil of insulated wire is connected to a galvanometer and a bar magnet with north pole is moved towards one face of the coil then, given situation is shown in the figure.
(i) Moved quickly towards the coil : A current is induced in anti-clockwise direction in the coil with respect to the side facing the north pole of the magnet and needle of galvanometer will deflect in one direction from zero position.
(ii) Moved quickly away from coil : A current is induced in clockwise direction in the coil with respect to the side facing the north pole of the magnet and the needle of the galvanometer will deflect in opposite direction from (i).
Short Answer: II
Question: When a magnet was pushed towards a solenoid, the galvanometer connected to the solenoid showed a deflection in right direction. When the same magnet was pulled away from the solenoid at a faster speed, what was the deflection in the galvanometer?
Answer.Deflection in galvanometer will be towards the left, because when the direction of movement of magnet is reversed, the direction of induced current is also reversed. The induced current is increased but it is flowing in opposite direction when the magnet is moving faster and in opposite direction.
Question: What is the role of split rings in an electric motor?
Answer.It act as a commutator in D.C (direct current) motor. The direction of current through the coil is reversed with the help of split rings after every half rotation of the coil, direction of current in the rotating coil remains the same and the coil continues to rotate in the same direction, thus producing direct current.
Question: Explain different ways to induce current in a coil.
Answer.(i) By changing the direction of current in the conductor.
(ii) By changing the magnetic field in around the coil.
Question: Imagine that you are sitting in a chamber with your back to one wall. An electron beam moves horizontally from back wall towards the front wall and by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer.
Current will move in the opposite direction to the flow of electrons. The direction of magnetic field will be downwards as shown in the figure.
Question: Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will the same current be induced in the coil B? Give reason.
Answer.No, the induced current in coil ‘B’ will change. It is because magnetic field produced in coil ‘A’ will change, therefore magnetic field induced in coil ‘B’ will also change. Hence induced current in the coil will also change.
Question: It is established that an electric current through a metallic conductor produces a magnetic field around it. Is there a similar magnetic field produced around a thin beam of moving (i) alpha particles,(ii) neutrons? Justify your answer.
Answer.(i) Yes, similar magnetic fields are produced. α-particles are positively charged particles, so current will be in the direction of motion of beam of particles.
(ii) No, in neutrons no current will be produced, as these are neutral particles.
Question: State Fleming’s right Hand Rule.
Answer.According to Fleming’s right hand rule, when the thumb, fore finger and the central finger of our right hand are kept perpendicular to each other when the thumb shows the direction of motion of the conductor, the forefinger shows the direction of magnetic field when current induced is in the direction of central finger as shown in the figure.
Question: Figure shows equipments used to demonstrate electromagnetic induction.
Two pieces of soft iron core ‘A’ and ‘B’ each having a coil of insulated wire wrapped around them. The coil around ‘A’ is connected to a switch and a cell. The coil around ‘B’ is connected to a galvanometer. When the switch is closed, the galvanometer shows a rapid deflection to the left before returning to zero.
(i) Explain why the galvanometer shows a rapid deflection to the left before returning to zero?
(ii) Explain what, if anything, would be observed on the galvanometer as the switch is opened?
Answer.(i) When the switch is closed, a changing magnetic field is produced in A which produces a change in magnetic field in ‘B’ resulting in induced current. However, the magnetic field in A becomes steady after sometime. Therefore, there is no more induced current in B as there is no change in the magnetic flux and the reading is zero.
(ii) When the switch is opened, there is deflection in the galvanometer but in the opposite direction.
The decreasing magnetic field in A produces an induced current in B. Since the change is reversed,the direction of induced current is also reversed.
Question: A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (a) pushed into the coil, (b) withdrawn from inside the coil, (c) held stationary inside the coil?
Answer.(a) It will show deflection.
(b) The deflection will be in the opposite direction.
(c) The galvanometer will not show any deflection.
Question: A magnetic compass needle is placed in the plane of paper near point A as shown in the figure. In which plane should a straight current carrying conductor be placed so that it passes through A and there is no change in the deflection of the compass? Under what conditions is the deflection maximum and why?
Answer.Straight current carrying conductor should be placed in the plane of paper. The magnetic field produced will be at 90° to the plane of paper and parallel to the vertical axis of magnetic needle. The deflection will be maximum when current carrying conductor is at 90°°to the plane of paper and magnetic field will be in the direction parallel to the plane of paper.
Question: Under what conditions a permanent electromagnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labeled circuit diagram.
Answer.(i) Direct current should be used.
(ii) Magnitude of current should be large.
(iii) The number of turns in solenoid are more and close to each other
like windings in an electric motor.
(iv) The soft core inside the solenoid should be made up of steel.
Question: What is meant by electromagnetic induction? State the rule which helps to determine the direction of induced current.
Answer.It is the phenomena of production of induced current and potential difference in a conductor by moving a magnet or if there is a change in magnetic field or flux.
Fleming’s right hand rule for determining the direction of induced current: Hold the thumb,the forefinger and central finger of your right hand perpendicular to each other in such a way that forefinger represents the direction of magnetic field, the thumb points in the direction of motion of conductor, then the central finger will give the direction of induced current in the conductor.
Question: State the condition for electromagnetic induction to take place. A cylindrical bar magnet is kept along the axis of circular coil as shown in the figure. Will there be a current induced in the coil, if the magnet is rotated about its axis? Discuss.
Answer.
• Either the coil or the magnet should be in motion
• If there is relative motion between a coil carrying current and coil not carrying current, there will be induced current in the second coil.
• No current will be induced because there is no change in magnetic field which is essential to produce induced current.
Question: (a) Draw a schematic labelled diagram of a domestic wiring circuit which includes
(i) a main fuse
(ii) a power meter
(iii) one light point
(iv) a power output socket
(b) In this circuit, on which wire of the circuit is the mains on/off switch connected?
Answer:
(b) As shown in this circuits, mains on off switch is connected with live wire and neutral wire.
Question: (a) Distinguish between the terms ‘overloading’ and ‘short-circuiting’ as used in domestic circuits.
(b) Why are the coils of electric toasters made of an alloy rather than a pure metal?
Answer: (a) Overloading is a situation in which there is sudden hike of current in the domestic circuit which may be caused by connecting too many
appliances into one socket. Short circuiting is a situation in which the live wire
(iii) Placed near its one face : No deffection of the needle of galvanometer is observed. The phenomena involved is called electromagnetic induction. comes in contact directly with neutral wire. Short circuiting can leads to overloading.
(b) Coils of electric toasters are made of an alloy rather than a pure metal because the resitivity value of alloy is greater than that of the pure metal. Greater the resistivity of a material, more will be the heat produced.
Question: Explain the principle and working of an electric motor with the help of a labelled diagram. What is the function of a split ring commutator?
Answer.
An electric motor converts electrical energy into mechanical energy. It works on the principle that a current carrying conductor placed in a magnetic field experiences a force.
Following are the essential parts of an electric motor.
(i) Coil: It is a rectangular coil of insulated copper wire having large number of turns.
(ii) A large permanent magnet provides strong magnetic field between its pole pieces. The coil rotates between these pole pieces.
(iii) Split rings: The two ends of coil are connected to two split rings, which are two halves of slip rings.
Working
When a current is passed through the coil, the direction of current in AB and CD is in opposite direction but both are perpendicular to magnetic field. Therefore, by Fleming’s left hand rule, arm AB of the coil experiences an upward force and arm CD experiences a downward force. These two forces being equal and opposite to each other form a couple which rotates the coil. Arms BC and DA are parallel to the field and the force between them is zero. The forces on AB and CD turns the coil in clockwise direction. After half revolution, the split rings change their position. So the direction of current in the coil reverses. The couple now acting on the coil again moves it in clockwise direction. Due to the function of split ring commutator and brushes, coil continues to turn in clockwise direction.
Split ring commutator changes direction after every half rotation, so that the direction of current going in the coil also reverses. As a result, the coil continues to rotate in one direction. So, the electrical energy given to the coil changes into mechanical energy
Question: (i) With the help of an activity, explain the method of inducing electric current in a coil with a moving magnet. State the rule used to find the direction of electric current thus generated in the coil.
(ii) Two circular coil-1 and coil-2 are kept close to each other as shown in the diagram.Coil-1 is connected to a battery and key and coil-2 with a galvanometer. State your observation
in the galvanometer:
(a) When key K closed;
(b) when key K is opened;
Give reason for your observations.
Answer.(i) • Take a coil of wire AB having a large number of turns.
• Connect the ends of the coil to a galvanometer as shown in figure.
• Take a strong bar magnet and move its north pole towards the end B of the coil.
• There is a momentary deflection in the needle of the galvanometer, say to the right. This indicates the presence of a current in the coil AB. The deflection becomes zero the moment
the motion of the magnet stops.
• Now withdraw the north pole of the magnet away from the coil.Now the galvanometer is deflected toward the left, showing that the current is now set up in the direction opposite to the first. Fleming’s right hand rule is used find the direction of electric current generated in the coil.
(ii) (a) The galvanometer needle deflects momentary in one direction because when the key is closed, magnetic field lines around coil-2 increases momentarily that causes induced current in coil-2.
(b) The galvanometer needle deflects momentarily but in opposite direction because when the key is opened, magnetic field lines around coil-2 decreases momentarily that causes induced current in coil-2.
Question: (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature (ii) Brushes (iii) Split ring
Answer.
(a) Fleming’s left-hand rule: Stretch the forefinger, middle finger and thumb of left hand in such a way that they are mutually perpendicular to each other. If the forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb shows the direction of force or motion of the current carrying conductor.
(b) Principle of working of electric motor: A coil carrying electric current placed in an external magnetic field experiences a force or torque.
(c) (i) Function of armature: Enhances the power of the motor/induces motion.
(ii) Function of brushes: Helps easy transfer of charge between the coil and the external circuit.
(iii) Function of split rings: Reverses the direction of current after every half rotation of the coil, so that coil can keep rotating continuously.
