CBSE Class 10 Science Chapter 13 Magnetic Effects Of Electric Current Short Answer Questions

CBSE Chapter 13 Magnetic Effects Of Electric Current Short Question And Answers

Question 1. List the properties of magnetic lines of force.
Answer: Those are closed curves that start in the air from the N-pole end at the S-pole and then return to the N-pole through the interior of the magnet.

1. No two magnetic lines of force can intersect each other.
2. The field lines are closer together in the regions of strong fields.
3. The field lines tend to contract lengthwise and expand sidewise.

Question 2. Why don’t two magnetic lines of force intersect each other?
Answer: If two lines of force intersect, then there will be two directions of the magnetic field at the point of intersection and a magnetic needle placed at this point should point towards these two directions, which is not possible.

Read and Learn More CBSE Class 10 Science Short Answer Questions

Question 3. 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 the magnetic field inside and outside the loop.
Answer: Each section of wire produces its concentric set of lines of force. By applying the right-hand thumb rule, we find that all the sections produce a magnetic field directed downward at all points inside the loop while at the outside points, the field is directed upwards. Hence, the magnetic field acts normally into the plane of paper at the points inside the loop and normally out ofthe plane of paper at points outside the loop.

Question 4. The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer: The uniform magnetic field B can be represented by equidistant parallel lines of force, as shown in the figure.

Choose the correct option.

1. The magnetic field inside a long straight solenoid-carrying current Is zero.
2. Decreases as we move towards its end
3. Increases as we move towards its end.
4. Is the same at all points.

Answer: 4. It is the same at all points

Question 5. In Activity 7.7, how do we think the displacement of rod AB will be affected if current in rod AB is increased; a stronger horse-shoe magnet is used; and the length of the rod AB is increased?
Answer: When the current in the red AB is increased, the force exerted on the conductor increases, so the displacement of the rod increases.

When a stronger horse-shoe magnet is used, the magnitude of the magnetic field increases. This increases the force exerted on the rod and the displacement of the rod. (Hi) Displacement of the rod is directly proportional to its length. Hence, there would be a larger displacement if the length of the rod AB is increased.

Question 6. State Fleming’s left-hand rule.
Answer: According to Fleming’s left-hand rule, if we stretch the forefinger, the middle finger and the thumb of our left hand are mutually perpendicular to each other and if the forefinger points in the direction ofthe magnetic field, the middle finger in the direction of current, then the thumb will point in the direction of motion or the force on the conductor.

Question 7. What is the principle ofan electric motor?
Answer: A current-carrying conductor when placed in a magnetic field experiences a force. The direction ofthis force is given by Fleming’s left-hand rule. This is the basis of an electric motor.

Question 8. What is the role ofthe split ring in an electric motor?
Answer: The split ring reverses the direction of current in the armature coil after every half rotation, i.e., it acts as a commutator. The reversed current reverses the direction ofthe forces acting on the two arms of the armature after every half rotation. This allows the armature coil to rotate continuously in the same direction.

Question 9. Explain different ways to induce a current in a coil.
Answer: A current can be induced in a coil by

1. If moving a magnet towards or away from the coil or vice versa, and
2. Changing current in the neighboring coil

Question 10. State the principle ofan electric generator.
Answer: An electric generator works on the principle of electromagnetic induction. When a closed coil is rotated in a uniform magnetic field with its axis perpendicular to the direction of the field, the magnetic field lines passing through the coil change and induce potential difference and hence a current is set up.

Question 11. Name some sources of direct current.
Answer: Some of the sources of direct current are dry cells, button cells, lead accumulators, etc.

Question 12. Which sources produce alternating current?
Answer: Alternating current is produced by A.C. generators of nuclear power plants, thermal power plants, hydroelectric power stations, etc.

Question 13. An electric oven with a kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer: The electric oven draws a current given by

⇒ \(\begin{aligned}
& \mathrm{I}=\frac{\mathrm{P}}{\mathrm{V}}=\frac{2 \mathrm{~kW}}{220 \mathrm{~V}} \\
& \mathrm{I}=\frac{2000 \mathrm{~W}}{220 \mathrm{~V}} \\
& \mathrm{I}=9.09 \mathrm{~A}
\end{aligned}\)

Thus, the electric oven draws current much more than the current rating of A. That is the circuit is overloaded. Due to excessive current, the fuse wire blows, and the circuit is broken.

Question 14. What precautions should be taken to avoid the overloading of domestic electric circuits?
Answer: As a result of overloading, the connecting wires get overheated and the appliances may get damaged.

To avoid this, the following safety measures must be taken:

The wires used in the circuit must be coated with good insulating materials like PVC, etc.

The circuit must be divided into different sections and a safety fuse must be used in each section. High-power appliances like air-conditioners, refrigerators, water heaters, etc., should not be used simultaneously.

Question 15. How does a solenoid behave like a magnet? Can you determine the north and south poles of a current-carrying solenoid with the help of a bar magnet1? Explain.
Answer: The magnetic field pattern produced by a solenoid is similar to that of a bar magnet.
Like a bar magnet, one end of the solenoid has N-polarity and the other end has Spolarity.

We bring the N-pole of the bar magnet near one end of the solenoid. If there is an attraction, then that end of the solenoid has south polarity and the other has north polarity. If there is a repulsion, then that end ofthe solenoid has north polarity and the other end has south polarity.

Question 16. When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer: When the conductor carries current in a direction perpendicular to the direction of the magnetic field, the force experienced by the conductor is largest.

Question 17. 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: According to Fleming’s left-hand rule, the magnetic field acts in a vertically downward direction. Note that the direction of the current will be opposite to that ofthe electron beam.

Question 18. Name some devices in which electric motors are used.
Answer: Electric motor is used ’n appliances like electric fans, washing machines, mixers, grinders, blenders, computers, MP3 players, etc.

Question 19. A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is pushed into the coil, withdrawn from inside the coil, or held stationary inside the coil?
Answer: An electric current is induced in the coil and the galvanometer shows a deflection.

An electric current is induced in the coil but in the opposite direction. The galvanometer shows a deflection in the reverse direction.

No current is induced in the coil. The galvanometer shows no deflection.

Question 20. Two circular coils A and B are placed close to each other. If the current in coil A is changed, will some current be induced in the coil B? Give a reason.
Answer: Yes. When the current in coil A is changed, some current is induced in the coil B. Due to the change in current in coil A, the magnetic field lines linked with coil A and coil B get changed. This sets up induced current in coil B.

Question 21. State the rule to determine the direction of a magnetic field produced around a straight conductor-carrying current, the force experienced by a current-carrying straight conductor placed in a magnetic field that is perpendicular to it, and the current induced in a coil due to its rotation in a magnetic field.
Answer: Right-hand thumb rule: If the current-carrying conductor is held in the right hand such that the thumb points in the direction of the current, then the direction of the curl of the fingers will give the direction of the magnetic field.

Fleming’s left-hand rule: Stretch the forefinger, the middle finger and the thumb ofthe left hand mutually perpendicular to each other. The forefinger points in the direction ofthe magnetic field, the middle finger in the direction of the current, then the
thumb points in the direction of force in the conductor.

Fleming’s right-hand rule: Stretch the thumb, forefinger, and middle finger of the right hand mutually perpendicular to each other.If the forefinger points in the direction of the magnetic field, the thumb in the direction of motion of the conductor, then the middle finger points in the direction of the current induced in the conductor.

Question 22. When does an electric short circuit occur?
Answer: As a result of the live wire touching the neutral wire, the resistance offered to the flow of current becomes almost zero and this is called short-circuiting. In this situation, a large current flows through the circuit, causing a spark or damage to the appliance.

Question 23. What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer: The earth wire connects the metallic body ofthe high-powered appliance to the earth. It is a safety measure that ensures any leakage of current of the metallic body of the appliance as it keeps its potential equal to that ofthe earth (zero volts) and the user may not get a severe electric shock.

Question 24. The horizontal component of Earth’s magnetic field at a place is uniform and its direction is south to north. A high current through a horizontal power line flows at this place from west to east. Consider two points A and B at equal distances from the wire, respectively above and below it. Giving reason explains where the fields are A and B.
Answer: According to the right-hand thumb rule, the direction of the magnetic field due to the current at A is from north to south and at B from south to north.

Therefore, at A earth’s field and field due to current are in opposite directions whereas at B they are in the same direction. So the field is more at B.

Question 25. Give some advantages of electromagnets over permanent magnets.
Answer: An electromagnet has the following advantages over a permanent magnet:

1. An electromagnet can produce a very strong magnetic field.
2. The strength of the magnetic field of an electromagnet can be increased/decreased by increasing/decreasing the strength of the current or the number of turns in the solenoid.
3. The polarity of an electromagnet can be reversed by sending the current in the reverse direction.

Question 26. Name and state the rule to determine the direction of force experienced by a straight conductor carrying current placed in a magnetic field that is perpendicular to it. Or State Fleming’s left-hand rule with a labeled diagram.
Answer: Fleming’s left-hand rule: Stretch the forefinger, the central finger, and the thumb of the left hand mutually perpendicular to each other. The forefinger points in the direction of the magnetic field, the central finger in the direction of current, and then the thumb points in the direction of force on the conductor.

Question 27. Two long parallel wires are hanging freely. If they are connected to a battery (i) in series and 2 in parallel, what would be the effect on their positions?
Answer: In series: The current flowing in them will be in the opposite direction. Hence, they will repel each other.

In parallel: The current flowing in them will be in the same direction. Hence, they will attract each other.

Question 28. What is the role of the fuse, used in series with any electrical appliance? Why should a fuse with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it.

If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off.

Question 29. A current through a horizontal power line flows in an east-to-west direction. What is the direction magnetic field at a point directly below it and a point directly above it?
Answer: The current is in the east-west direction. Applying the right-hand thumb rule, we get that the direction of the magnetic field at a point below the wire is from north to south. The direction of the magnetic field at a point directly above the wire is from south to north.

Question 30. Explain why a fuse should be joined with the live wire and not with the neutral wire in a domestic circuit.
Answer: In a domestic circuit, the phase wire always has a much higher potential than the neutral wire. Moreover, the neutral wire is connected to the earth at the substation. Thus, during a short circuit, the fuse will break the connection with the neutral wire and not the live wire.

Question 31. A current I passes through a circular loop C and a solenoid AB as shown below:

1. What is the polarity of (a) the force ofthe loop you are looking at? (b) the end of the solenoid?
2. What is the direction ofthe magnetic field at the center ofthe loop?

Answer: The face of the loop will behave as a North Pole.

1. End B will also behave as a North Pole.
2. Straight and parallel to the axis of the solenoid.

Question 32. Can two magnetic lines of force intersect? Justify your answer.
Answer: No, if two magnetic lines of forces intersect, then there will be two tangents and hence two directions of the magnetic field at the point of intersection. This is not possible.

Question 33. Define a solenoid. How is it different from a coil? 
Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The strength of the magnetic field inside a coil varies while in the solenoid case, it is the same.

Question 34. State Faraday’s Laws of electromagnetic induction.
Answer: Faraday put forward the following laws: Faraday’s laws of electromagnetic induction.

1. Whenever the magnetic field (flux) linked with a coil changes, an induced EMF is produced.
2. The induced emflasts as long as the change in magnetic field (flux) continues.
3. The induced emf in the closed loop equals the negative rate of change of magnetic field (flux) through the loop.

Question 35. State Oersted observation. How can it be shown that a magnetic field exists around a wire through which a direct electric current is passing?
Answer: A magnetic needle brought close to a straight current-carrying wire aligns itself perpendicular to the wire, reversing the direction of current reverses the direction of deflation. This shows that the current-carrying wire is associated with a magnetic field.

Question 36. Draw the patterns of magnetic field lines due to a bar magnet. The magnetic field lines
are closed curves. Why?
Answer: Inside the magnet, the direction of field lines is from its south pole to its north pole. So the magnetic field lines are closed curves

Question 37. An alpha particle (+ve charged particle) enters a magnetic field at a right angle as shown in the figure. Explain with the help of a relevant rule, the direction of force acting on the alpha particle.

Answer: According to Fleming’s left-hand rule, if the forefinger points in the direction ofthe magnetic field and the central finger points in the direction of a current, the thumb gives the direction of the force acting on the conductor. So the force will act in the upward direction of the alpha particle.

Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors that can produce them.

Answer: It represents the magnetic field lines produced by a current-carrying circular loop.

It represents the magnetic field lines produced by a solenoid

Question 38. Explain the right-hand thumb rule and cork and screw rule to find the magnetic field due to a current-carrying conductor.
Answer: Imagine a current-carrying conductor held in your right hand such that the thumb points in the direction of current, then the curl of your fingers encircling the conductor will give the direction of magnetic field lines around the conductor. Maxwell’s cork screw rule (Right-hand screw rule):

Imagine a right-handed screw to be rotated in the direction of current, then the direction of rotation gives the direction of magnetic field lines.

Question 39. What is the nature of the magnetic field produced by a current-carrying circular coil? Explain with the help ofan experiment.
Answer: Bend a copper wire in a circular shape. Pass the coil through a cardboard. Connect the free ends ofthe coil to a battery and a key. Sprinkle some iron filings on the cardboard.

Put on the key, you will find that the iron filings arrange themselves in the form of concentric circles. The magnetic lines of force near each segment of wire are circular and form concentric circles. Whereas the lines of force near the center of the coil are almost straight fines. Note that at the center of the coil, the magnetic field is uniform and perpendicular to the plane of the coil.

Question 40. In a pattern of magnetic field lines due to a bar magnet, how can the regions of relative strength be identified1? Compare the strength of the field near the poles and middle of a bar magnet
Answer:

The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field fines.

The strength of the field near the poles is highest and in the middle of a bar magnetite is the lowest.

Question 41. State one main difference between AC and DC. Why ac is preferred over DC for long-range transmission of electric power? Name one source for each of DC and AC.
Answer: The DC always flows in one direction while AC reverses its direction periodically. This is because in the case of AC electric power can be transmitted over long distances without much loss of energy.

1. Source of AC- AC generator
2. Source of- DC generator/cell

Question 42. Student experiments to study the magnetic effect of current around a current-carrying straight conductor with the help of a magnetic compass. He reports that:

1. The degree of deflection ofthe magnetic compass increases when the compass is moved away from the conductor.
2. the degree of deflection of the magnetic compass increases when the current through the conductor is increased.
3. Which of the above observations ofthe student appears to be wrong and why?

Answer: The first observation is wrong. Because as the distance from the conductor increases, the strength ofthe magnetic field will decrease. So the degree of deflection ofthe compass should decrease instead of increasing.

Question 43. Draw magnetic field lines produced around a current carrying a straight conductor passing through cardboard. How will the strength of the magnetic field change, when the point where the magnetic field is to be determined, is moved away from the straight wire carrying constant current? Justify your answer:
Answer: The diagram is as shown:

We will move a compass needle away from the straight wire. When it is moved away from the straight wire, the deflection of the needle decreases which implies that the strength of the magnetic field decreases.

Question 44. A student while studying the force experienced by a current-carrying conductor in a magnetic field records the following observations.

1. The force experienced by the conductor increases as the current is increased.
2. The force experienced by the conductor decreases as the strength ofthe magnetic field is increased
3. Which of the two observations is correct and why?

Answer: The observation is correct.

Question 45. Magnetic field lines are shown in the given diagram. A student makes a statement that the magnetic field at X is stronger than at Y. Justify this statement. Also, redraw the diagram and mark the direction of magnetic field lines.
Answer: The relative strength ofthe magnetic field is shown by the degree of closeness ofthe field lines. The field lines are closer at X than at Y. Therefore, the field is stronger at X where the field lines are crowded. The diagram is as shown:

Because the force experienced by a current-carrying conductor in a magnetic field is proportional to the strength of the current.

Question 46. How does the strength ofthe magnetic field at the center of a circular coil of a wire depend on:

1. Radius Ofthe Coil
2. Number of Ofturns In The Coil

Answer: 1 As the radius increases, the field decreases.

2. The field produced is directly proportional to the number of turns in the coil.

Question 47. What is a fuse? How does it function?
Answer: An electric fuse is a device that is used to limit the current in an electric circuit. The use of a fuse is to safeguard the circuit and the appliances connected to it from being damaged.

The fuse is a short piece of wire made of a material having a low melting point. When an electric current is passed through it, the fuse gets heated. If the current passing through the fuse exceeds the safe limit, the heat produced melts the fuse and this breaks the circuit.

Question 48. What is meant by the term “magnetic field lines”? List two properties of magnetic field lines.
Answer: A magnetic field line is a path that will be followed by a “hypothetical” north pole in the magnetic field of another magnetite that is allowed to move freely. Two properties of magnetic field lines are:

1. Two magnetic field lines do not intersect each other.
2. They travel from the north to the south pole of a magnet outside the magnet and from the south to the north pole inside the magnet.

Question 49. Draw a rough sketch of the pattern of the field lines due to:

1. Current flowing into a circular coil and
2. Solenoid carrying current

Answer: The sketches are shown below:

Question 50. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected, if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength of the magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 51. As shown in the figure, a magnetic compass needle is placed on a paper plane near point A. In which plane should a straight current-carrying conductor be positioned so that it passes through A and there is no change in the deflection ofthe compass? Under what condition is the deflection maximum and why?
Answer: In the plane of the paper itself. The axis of the compass is vertical and the field due to the conductor is also vertical. It could result in a dip of the compass needle which is not possible in this case (dips result only if of compass is horizontal). The deflection is maximum when the conductor through Ais perpendicular to the plane paper and the field due to its maximum in the plane of the paper.

Question 52. Under what conditions permanent electromagnet is obtained if a current-carrying solenoid is used? Support your answer with the help of a labeled circuit diagram.
Answer: The current through the solenoid should be a direct current.

The rod inside is made of a magnetic material such as steel.

Question 53. AB is a current-carrying conductor in the plane of the paper as shown in the figure. What are the directions of the magnetic field produced by it at the points P and Q? Given; > r2, where will the strength ofthe magnetic field be larger?
Answer: Into the plane of paper at P and out of at Q. The strength of the magnetic field is larger at the point located closer i.e. at Q

Question 54. A magnetic compass shows a deflection when placed near a current-carrying wire. How will the deflection of the compass be affected if the current in the wire is increased? Support your answer with a reason.
Answer: The deflection increases. The strength magnetic field is directly proportional to the magnitude of current passing through the straight conductor.

Question 55. 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 alpha particles, and neutrons’? Justify your answer.
Answer:

1. Yes, Alpha particles being positively charged constitute, current to the direction of motion.
2. No, the neutrons being electrically neutral constitute no current.

Question 56. What does the direction of thumb indicate in the right-hand thumb rule? In what way
this rule is different from Fleming’s left-hand rule?
Answer: The thumb indicates the direction of current in the straight conductor held by curled fingers, whereas Fleming’s left-hand rule gives the direction of force experienced by the current-carrying conductor placed in an external magnetic field.

Question 57. Meena draws magnetic field lines of field close to the axis of a current-carrying circular
loop. As she moves away from the center ofthe circular loop she observes that the lines keep
on diverging. How will you explain her observation?
Answer: The strength of the magnetic field falls as distance increases. This is indicated by the decrease in the degree of closeness of the lines of field.

Question 58. What does the divergence of magnetic field lines near the ends of a current carrying a straight solenoid indicate?
Answer: The divergence, that is, the falling degree of closeness of magnetic field lines indicates
the fall in strength of the magnetic field near and beyond the ends of the solenoid.

Question 59. Name four appliances wherein an electric motor, a rotating device that converts electrical energy to mechanical energy, is used as an important component. In what respect motors are different from generators?
Answer: Electric fans, mixers, washing machines, computer drives, etc. Motors convert electrical energy into mechanical energy whereas generators convert mechanical energy into electrical energy.

Question 60. What is the role ofthe two conducting stationary brushes in a simple electric motor?
Answer: The brushes are connected to the battery and touch the outer side of two halves of the split ring whose inner sides are insulated and attached to the axle.

Question 61. What is the difference between a direct current and an alternating current? How many times does AC used in India change direction in one second?
Answer: Direct current always flows in one direction but the alternating current reverses its direction periodically. The frequency of AC in India is 50 Hz and in each cycle it alters direction twice. Therefore AC changes direction 2 x 50 = 100 times in one second.

Question 62. What is the role of the fuse, used in series with an electrical appliance? Why should a fuse
with a defined rating not be replaced by one with a larger rating?
Answer: Fuse is used for protecting appliances due to short-circuiting or overloading. The fuse is rated for a certain maximum current and blows off when a current more than the rated value flows through it. If a fuse is replaced by one with larger ratings, the appliances may get damaged while the protecting fuse does not burn off. This practice of using a fuse of improper rating should always be avoided.

Question 63. Why does a magnetic compass needle pointing North and South in the absence of a nearby magnet get deflected when a bar magnet or a current-carrying loop is brought near it? Describe some salient features of the magnetic lines of field concept.
Answer: Current carrying loops behave like bar magnets and both have their associated lines of field. This modifies the already existing earth’s magnetic field and a deflection results. The magnetic field has both direction and magnitude. Magnetic field lines emerge from the N-pole and enter the S-pole.

The magnetic field strength is represented diagrammatically by the degree of closeness of the field lines. Field lines cannot cross each other as two values of net field at a single point cannot exist. Only one value, a unique net value, can exist. If in a given region, lines of field are shown to be parallel and equispaced, the field is understood to be uniform.

Question 64. With the help of a labelled circuit diagram illustrate the pattern of field lines of the magnetic field around a current carrying a straight long conducting wire. How is the right-hand thumb rule useful to find the direction of the magnetic field associated with a current-carrying conductor?
Answer: The right-hand thumb rule states that if a current-carrying straight conductor is supposedly held in the right hand with the thumb pointing towards the direction of current, then the fingers will wrap around the conductor in the direction ofthe field lines of the magnetic field.

Question 65. Explain with the help of a labeled diagram the distribution of magnetic field due to a current through a circular loop. Why is it that if a current-carrying coil has n turns, the field produced at any point is n times as large as that produced by a single turn?
Answer: The magnetic field (B) produced by current carrying N circular wire depends on:

• Amount of current flowing through wire (I):
  • B∞I
• Number of turns on the circular wire (N)
  • B∞N

If there is a circular coil having N turns, the field Magnetic force (lines) due to produced is N times as large as that produced by a current carrying through a loop single turn.

Magnetic Effects Of Electric Current Multiple-Choice Questions

Question 1. Choose the incorrect statement from the following regarding magnetic lines of the field.

1. The direction of the magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points
2. Magnetic field lines are closed curves
3. Magnetic field lines are parallel and equidistant, they represent zero field strength
4. The relative strength of the magnetic field is shown by the degree of closeness of the field lines.

Answer: 3. If magnetic field lines are parallel and equidistant, they represent zero field strength

Question 2. If the key in the arrangement is taken out (the circuit is made open) and magnetic field lines are drawn over the horizontal plane ABCD, the lines are

1. Concentric Circles
2. Elliptical In Shape
3. Straight Lines Parallel to Each Other
4. Concentric Circles Near The Point O But Of Elliptical Shapes As We Go Away From It

Answer: 3. Straight Lines Parallel to Each Other

Question 3. A circular loop placed in a plane perpendicular to the plane of paper carries a current when the key is ON. The current as seen from points A and B (in the plane of paper and on the axis of the coil) is anticlockwise and clockwise respectively. The magnetic field lines point from B to A. The N-pole of the resultant magnet is on the face close to

1. A
2. B
3. A if the current is small, and B if the current is large
4. B if the current is small and the current is large

Answer: 1. A

Question 4. For a current in a long straight solenoid, N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is

1. The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all the points inside the solenoid
2. The strong magnetic field produced inside the solenoid can be used to magnetize a piece of magnetic material like soft iron when placed inside the coil
3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet
4. The N- and S-poles exchange position when the direction of current through the solenoid is reversed

Answer: 3. The pattern of the magnetic field associated with the solenoid is different from the pattern ofthe magnetic field around a bar magnet.

Question 5. A uniform magnetic field exists in the plane of paper pointing from left to right as shown in the given figure. In the field an electron and a proton move as shown. The electron and the proton experience

1. Forces Both Pointing Into The Plane of Paper
2. Forces Both Pointing Out Ofthe Plane Of paper
3. Forces Pointing Into The Plane Ofpaper And Out Of The Plane Ofpaper, Respectively
4. Force Pointing Opposite And Along The Direction Of The Uniform Magnetic Field Respectively

Answer: 1. Forces Both Pointing Into The Plane Ofpaper

Question 6. Commercial electric motors do not use

1. An Electromagnet To Rotate The Armature
2. Effectively Large Number of Turns of Ofconducting Wire In The Current Carrying Coil
3. A Permanent Magnet To Rotate The Armature
4. A Soft Iron Core On Which The Coil Is Wound

Answer: 3. A Permanent Magnet To Rotate The Armature

Question 7. In the arrangement shown in given figure, there are two coils wound on a non-conducting cylindrical rod. Initially, the key is not inserted. Then the key is inserted and later removed. Then

1. The Deflection In Thegalvanometerremains Zero Throughout
2. There Is A Momentary Deflection In The Galvanometer But It Dies Out Shortly And There Is No Effect When The Key Is Removed
3. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In The Same Direction
4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Answer: 4. There Are Momentary Galvanometer Deflections That Die Out Shortly; The Deflections Are In Opposite Direction

Question 8. Choose the incorrect statement

1. Fleming’s right-hand rule is a simple rule to know the direction of the induced current
2. The right-hand thumb rule is used to find the direction of magnetic fields due to current-carrying conductors
3. The difference between the direct and the alternating current is that the direct current always flows in one direction, whereas the alternating current reverses its direction periodically
4. In India, the AC changes direction after every — second.

Answer: 4. In India, the AC changes direction after every — second.

Question 9. A constant current flows in a horizontal wire in the plane ofthepaper from the east to the west as shown in the figure. The direction of the magnetic field at a point will be North to South

1. Directly Above The Wire
2. Directly Below The Wire
3. At A Point Located In The Plane Of The Paper, On The North Side Of The Wire
4. At A Point Located In The Plane Ofthe Paper, On The South Side Ofthe Wire

Answer: 2. Directly Below The Wire

Question 10. The Strength Magnetic Field Inside A Long Current Carrying a Straight Solenoid Is

1. More At The Ends Than At The Centre
2. Minimum In The Middle
3. Same At All Points
4. Found To Increase From One End To The Other

Answer: 3. Same At All Points

Question 11. To Convert An AC generator Into a DC generator

1. Split-Ring Type Commutator Must Be Used
2. Slip Rings And Brushes Must Be Used
3. A Stronger Magnetic Field Has To Be Used
4. A Rectangular Wire Loop Has To Be Used

Answer: 1. Split-Ring Type Commutator Must Be Used

Question 12. The Most Important Safety Method Used For Protecting Home Appliances From short-circuiting or Overloading Is

1. Earthing
2. Use Ofstabilizers
3. Use Office
4. Use Ofelectric Meter

Answer: 2. Use Of stabilizers

Question 13. Which ofthe following correctly describes the magnetic field near a long straight wire1?
Answer:

1. The field consists of straight lines perpendicular to the wire.
2. The field consists of straight lines parallel to the wire.
3. The field consists of radial lines originating from the wire.
4. The field consists of concentric circles centered on the wire.

Answer: 4. The magnetic field near a long straight wire the field consists of concentric circles centered on the wire.

Question 14. The phenomenon of electromagnetic induction is

1. The Process of Charging A Body.
2. The Process of Generating Magnetic Field Due To A Current Passing Through A Coil.
3. Producing Induced Current In A Coil Due To Relative Motion Between A Magnet And The Coil.
4. The Process Ofrotating A Coil Ofan Electric Motor.

Answer: 3. Electromagnetic induction produces induced current in a coil due to relative motion between a magnet and the coil.

Question 15. The device used for producing electric current is called a

1. Generator
2. Galvanometer
3. Ammeter
4. Motor

Answer: 1. A generator is used for producing electric current.

Question 16. The essential difference between an AC generator and a DC generator is that

1. AC generator has an electromagnet while a DC generator has a permanent magnet.
2. DC generator will generate a higher voltage.
3. AC generator will generate a higher voltage.
4. AC generator has slip rings while the DC generator has a commutator.

Answer: 2. The AC generator has slip rings while the DC generator has a commutator.

Question 17. At the time short circuit, the current in the circuit

1. Reduces Substantially
2. Does Not Change
3. Increase Heavily
4. Vary Continuously

Answer: 3. At The Time Of a Short Circuit The current in the circuit increases greatly

Question 18. State whether the following statements are true or false.

1. An electric motor converts mechanical energy into electrical energy.
2. An electric generator works on the principle of electromagnetic induction.
3. The field at the center of the long circular coil carrying current will be parallel straight
   lines.
4. A wire with green insulation is usually the live wire ofan electric supply.

Answer: 1. False. It converts electrical energy into mechanical energy.

1. True.
2. True. The field is almost uniform at the center of the coil.
3. False. The ware with green insulation is usually the live wire.

Question 19. What happens to the deflection of the compass needle placed at a point near current carrying straight conductor:

1. If the current is increased?
2. If the direction of the current in the conductor is changed (reversed)?
3. If the compass is moved away from the conductor?

Answer:

1. The deflection of the compass needle increases.
2. The direction of deflection in the compass needle changes.
3. The deflection of the compass needle decreases.

Question 20. A coil of insulated wire is connected to a galvanometer. Explain what happens if a bar magnet with its north pole towards one face ofthe coil is:

1. Moved Quickly Towards The Coil,
2. Kept Stationary Inside The Coil, And
3. Moved Quick Away From The Coil?

Answer: The increasing magnetic field induces current in the coil as a result of which the galvanometer shows momentary deflection (say towards the right).

No change in a magnetic field, no induced current, and deflection zero.

The magnetic field decreases, the induced current is produced in the coil and the galvanometer shows momentary deflection in the opposite direction (say towards the left).

Question 21. Which of the following properties of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)

1. Mass
2. Speed
3. Velocity
4. Momentum

Answer: The correct options are (c) and (d). The magnetic force acts perpendicular to the direction of motion of the proton. It does not change its mass and speed but changes its direction of motion. So both velocity and momentum get changed.

Question 22. A positively charged particle (alpha-particle) projected towards the west is deflected towards the north by a magnetic field. The direction of the magnetic field is

1. Towards South
2. Towards East
3. Downward
4. Upward

Answer: The correct option is 4. This is by Fleming’s left-hand rule

Question 23. Choose the correct option.
Answer: A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each

1. Two Revolutions
2. One Revolution
3. Half revolution
4. One-Fourth Revolution

Answer: The correct option is (b).

Question 24. Name two safety measures commonly used in electric circuits and appliances.

Answer:

1. Earthing
2. Electric fuse