# Exam Question for Class 10 Science Chapter 13 Magnetic Effect of Electric Current

Please refer to below Exam Question for Class 10 Science Chapter 13 Magnetic Effect of Electric Current These questions and answers have been prepared by expert Class 10 Science teachers based on the latest NCERT Book for Class 10 Science and examination guidelines issued by CBSE, NCERT, and KVS. We have provided Class 10 Science exam questions for all chapters in your textbooks. You will be able to easily learn problems and solutions which are expected to come in the upcoming class tests and exams for standard 10th.

## Chapter 13 Magnetic Effect of Electric Current Class 10 Science Exam Question

All questions and answers provided below for Exam Question Class 10 Science Chapter 13 Magnetic Effect of Electric Current are very important and should be revised daily.

Exam Question Class 10 Science Chapter 13 Magnetic Effect of Electric Current

Question:The change in magnetic field lines in a coil is the cause of induced electric current in it. Name the underlying phenomenon.
Answer: The change in magnetic field lines in a coil is the cause of induced current in it and the phenomenon is electromagnetic induction.

Question: Why is current induced in the secondary coil when current is changed in the primary coil?
Answer: Current is induced in the secondary coil as the magnetic field lines associated with it are changing due to change in current in the primary coil resulting in change in magnetic field associated with the primary coil.

Question: What is the function of a galvanometer in a circuit?
Answer: Galvanometer is an electromechanical instrument used to detect or indicate the presence of current by deflection in a circuit.
It consists of a pointer which can move along a scale with zero marked at its centre and is attached to a moving coil.

Question: What happens when an iron core is inserted into a current carrying solenoid?
Answer: When an iron core is inserted into a current carrying solenoid, strength of the magnetic field produced inside the solenoid increases and it forms an electromagnet.

Question: Define the term induced electric current.
Answer: Induced electric current: It is the current which is created due to the relative motion of coil or magnet. The induced current is found to be the
highest when the direction of motion of the coil is at right angles to the magnetic field.

Question: Under what condition does a current carrying conductor kept in a magnetic field experience maximum force?
Answer: A current carrying conductor kept in a magnetic field experiences maximum force when direction of current is at right angles to the direction of the magnetic field according to Fleming’s left hand rule.

Question: A straight wire carrying electric current is moving out of a plane of paper and is perpendicular to it. What is the direction of the magnetic field?
Answer: Magnetic field lines will be concentric circles in the plane of the paper and in anti-clockwise direction which can be found out by applying Right hand thumb rule.

Question: What is indicated by crowding of magnetic field lines in a given region?
Answer: The crowding of magnetic field lines in a given region indicates that the magnetic field is stronger in that region.

Question: Why do commercial motors use a soft iron core on which the coil is wound?
Answer: Commercial motors use a soft iron core on which the coil is wound to increase the power of the electric motor.

Question: Why does a compass needle get deflected when brought near a bar magnet?
Answer: The needle of a compass is a small magnet.
When a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet and therefore the compass needle gets deflected.

Question: Two coils of insulated copper wire are wound over a non-conducting cylinder as shown. Coil 1 has comparative large number of turns.

(1) Key K is closed.
(2) Key K is opened.
Give reason for each of your observations
Answer: (1) Key K is closed.
When key K is closed, (means the current is flowing through coil), we will observe that the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero. This indicates that there is a momentary current in coil-2.
(2) Key K is opened.
When Key K is opened (means the current is not flowing through the coil), we will observe that the needle momentarily moves, but to the opposite side. It means that now the current flows in the opposite direction in coil-2.

Question: What happens to the magnetic field lines due to a current-carrying conductor when the current is reversed?
Answer: When we reverse the direction of electric current flowing in the current-carrying conductor, then the direction of magnetic field lines produced by it are also reversed. Question: Under what conditions permanent electro-magnet is obtained if a current carrying solenoid is used? Support your answer with the help of a labeled circuit diagram.
Answer: The following conditions are required to obtain permanent electromagnet when a current carrying solenoid is used:
(1) Rod inside the solenoid should be made of magnetic material like steel which should retain magnetic properties for a long time after magnetization.
(b) The current through the solenoid should be direct current.
(c) The number of turns in the solenoid should be large and closely packed, so that a strong uniform magnetic field inside it is produced.

Question: Why cannot two magnetic field lines intersect?
Answer: Two magnetic field lines never intersect because the resultant force on a north pole at any point can only be in one direction. But if two magnetic field lines intersect one another, then the resultant force on a north pole placed at the point of intersection will be along two directions, which is not possible.

Question: Draw magnetic field lines around a bar magnet.
Answer: Magnetic field lines around a magnet :

Question: List the properties of magnetic field lines?
Answer: Properties of magnetic field lines:
(1) Magnetic field is a quantity that has both direction and magnitude.
(2) They emerge from the north pole of a magnet and enter at the south pole of the magnet.
(3) Inside the magnet, the direction of field lines is from south pole to its north pole. Hence, magnetic field lines are closed curves.
(4) The relative strength of the magnetic field is shown by the degree of closeness of the field lines. Crowded field lines represent the strong magnetic field.
(5) The magnetic field at any point is represented by the tangent at that point.
No two field lines intersect each other. If they intersect, it would mean that at point of intersection there would be two field directions, which is not possible.
(6) They are dense close to the poles and sparse away from them. It means magnetic field is strongest around poles of the magnet

Question: (A) Draw the pattern of magnetic field lines due to a magnetic field through and around a current carrying circular loop.
(B) Name and state the rule to find out the direction of magnetic field inside and around the loop.

(B) The magnetic field lines are concentric circles at every point of a current carrying circular loop. The direction of magnetic field of every section of the circular loop can be found be using the right hand thumb rule.
(1) The magnetic field lines are near circular at the points where the current enters or leaves the coil.
(2) Within the coil, the field lines are in the same direction.
(3) Near the centre of the coil, the magnetic field lines are almost parallel to each other.
(4) At the centre of the coil, the plane of magnetic field lines is at right angle to the plane of the circular coil.

Question: What are the differences between permanent magnet and electromagnet?
Answer: Difference between permanent magnet and electromagnet:

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 condition is the deflection maximum and why?

Answer: The straight current carrying conductor should
be placed in the same plane as that of paper. According to the Right hand thumb rule, the direction of the magnetic field is perpendicular to the direction of the current and if a magnetic compass is brought closer to the current carrying conductor, the deflection is maximum. But, when the needle is placed near the point A on the plane as that of the paper as given in the figure, there is no deflection.

Question: Can a freely suspended current carrying solenoid stay in any direction? Justify your answer. What will happen when the direction of current in the solenoid is reversed?
Explain.
Answer: Solenoid is a closely bound cylindrical coil of insulated metallic wire. A current carrying freely suspended solenoid behaves like a magnet and when suspended freely, it rests in north-south direction.
A current carrying solenoid behaves like a bar magnet with fixed polarities at its ends. The end of the current carrying solenoid at which the current flows anticlockwise behaves as a north pole while that end at which the direction of current is clockwise behaves as a south pole. The direction of magnetic field is always perpendicular to the direction of current flow and the magnitude of the magnetic field inside a solenoid is directly proportional to the current flowing through the solenoid.
Thus, when the current through the solenoid is reversed, the direction of magnetic field is reversed.

Question: With the help of a labeled circuit diagram,illustrate the pattern of field lines of the magnetic field around a current-carrying straight long conducting wire. How is the right hand thumb rule useful in finding the direction of a magnetic field associated with a current-carrying conductor?
Answer: To be able to easily comprehend the direction of field lines around a current carrying conductor, we fix the straight conducting wire (PQ) at the centre (O) of a cardboard and sprinkle some iron fillings on the cardboard. Now we connect the conducting wire to terminals of a battery through a variable resistor, an ammeter (A) and a key (K).

As you can see in the image above, when current is passed through the conductor, iron fillings rearrange themselves in concentric circles (due to magnetic fields produced).
The arrows in the circles show the direction of magnetic field lines. The arrow just above P (or after Q) shows the direction of current flow.
We used Fleming right-hand thumb rule (as shown in the image below) to identify the flow of current and field lines.

In this rule, if a current carrying straight wire conductor is held by the right hand such that the thumb points towards the direction of current, then the fingers will wrap around the conductor in the direction of the field lines of the magnetic field.

Question: Name, state and explain with an example the rule used to determine the direction of force experienced by a current carrying conductor placed in a uniform magnetic field.
Fleming’s left-hand rule is used to determine the direction of force experienced by a current carrying conductor placed in a uniform magnetic field.

Fleming’s left-hand rule states that: stretch the thumb, fore finger and middle finger of the left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
Example: When an electron enters a magnetic field at right angle, the direction of force on electron is perpendicular to the direction of magnetic field and current according to this rule.

Question: A current through a horizontal power line flows in west to east direction.
(A) What is the direction of the magnetic field at a point directly above it and at a point directly below it?
(B) Name the rule used to determine:
(1) The direction of force when a current carrying wire is placed in a strong magnetic field.
(2) magnetic field in a current carrying conductor.
Answer: (A) The current is in the east-west direction.
Applying the right-hand thumb rule, we get that the direction of magnetic field at a point above the wire is from south to north or anticlockwise direction. The direction of magnetic field at a point directly below the wire is north to south or clockwise direction.
(B) (1) According to Fleming’s left-hand rule, hold the forefinger, the centre finger and the thumb of your left hand at right angles to one another.
Adjust your hand in such a way that the forefinger points in the direction of the magnetic field and the centre finger points in the direction of current, then the direction in which the thumb points, gives the direction of the force acting on the conductor.
(2) According to Maxwell’s right hand thumb rule: Imagine that you are holding the current-carrying wire in your right hand so that your thumb points in the direction of current, then the direction in which your fingers encircle the wire will give the direction of the magnetic field lines around the wire.

Question: State the rule to determine the direction of a (A) magnetic field produced around a straight conductor-carrying current, (B) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (C) current induced in  a coil due to its rotation in a magnetic field.
Answer: Rule to determine the direction:
(A) Right hand thumb rule which states that that if one holds a straight current carrying conductor with right hand such that the thumb points towards the direction of current, then fingers will wrap around the conductor in the direction of field lines of the magnetic field.
This rule determines the magnetic field produced around a straight conductor carrying current.
(B) Fleming’s Left Hand Rule, which states that if the first finger points in the direction of magnetic field and second finger in the direction of current, then the thumb will point in the direction of motion or the force acting on the conductor.
This determines force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it.
(C) Fleming’s Right Hand Rule, which states that if the forefinger indicates the direction of the magnetic field and thumb shows the direction of motion of conductor, then the middle finger will show the direction of induced current.
This rule determines the current induced in a coil due to its rotation in a magnetic field.

Question: (A) Why don’t two magnetic field lines ever intersect each other? Explain.
(B) ‘‘The magnetic field is said to be uniform inside a current carrying solenoid.’’ Why?
(C) State Fleming’s left hand rule.
(D) Enlist two factors that enhance the power of commercial motors.
Answer: (A) Two magnetic field lines can never cross each other because it would mean that at the point of intersection the compass needle would point towards two directions simultaneously which is not possible.
(B) The magnetic field lines inside a current carrying solenoid are in the form of parallel straight lines. This indicates that the magnetic field is the same (uniform) at all points inside the solenoid.
(C) Fleming’s left hand rule:
Stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular. If the first finger points in the direction of the magnetic field, the second finger in the direction of current, then the thumb will point in the direction of motion.
(d) Any two factors:
(i) Strength of electromagnet
(ii) Large number of coil/turns of the conducting wire
(iii) A soft iron core on which the coil is wound.Question: (A) A coil of insulated wire is connected to a galvanometer. What would be observed if a strong bar magnet with its south pole towards one face of the coil is:
(i) moved quickly toward it?
(ii) moved quickly away from it?
(iii) held stationary near it?
(B) Name the phenomena involved.
(C) State the conclusion based on the observations in (i), (ii) and (iii).
Answer: (A) A coil of insulated wire is connected to a galvanometer. When a strong bar magnet with its south pole facing towards one face of coil is:
(i) Moved quickly towards: These is a momentary deflection in the needle of the galvanometer, say to the left. This indicates the presence of current in the coil.

(ii) Moved quickly away from it: The galvanometer is deflected towards the left, showing that current is now set up in the direction opposite to the first, say to the right.
(iii) Held stationery near it: The galvanometer does not show any deflection indicating that no current is produced in the coil.
(B) The phenomenon involved is Electro- magnetic induction.
(C) Conclusion: The motion of strong bar magnet with respect to coil produces an induced potential difference, which sets up an induced electric current in the coil.

Question: A student fixes a sheet of white paper on a drawing board. He places a bar magnet in the centre of it. He sprinkles some iron filings uniformly around the bar magnet. Then he taps the board gently and observes that the iron filings arrange themselves in a particular pattern.
(A) Why do the iron filings arrange in a pattern?
(B) What do the lines along which the iron filings align represent?
(C) What does the crowding of iron filings at the end of the magnet indicate?
(D) List the properties of magnetic field lines.
Answer: (A) Iron filings arrange in a pattern because a magnetic field exists around a magnet and force is exerted by the magnet within its magnetic field.
(B) The lines represent magnetic field lines.
(C) The crowding of iron filings at the end of the magnet indicates that the strength of magnetic field is maximum near the poles of the magnet.
(D) Properties of magnetic field lines:
(1) Magnetic field lines are closed continuous curves.
(2) The tangent at any point on the magnetic field lines gives the direction
of magnetic field at that point.
(3) No two magnetic field lines can intersect each other.
(4) They are crowded in a region of strong magnetic field and are far from each other in a region of weak magnetic field.

Question: (A) What are magnetic field lines? How is the direction of magnetic field at a point in a magnetic field determined using field lines?
(B) Two circular coils ‘X’ and ‘Y’ are placed close to each other. If the current in the coil ‘X’ is changed, will some current be induced in the coil ‘Y’? Give reason.
(C) State ‘Fleming’s right hand rule”.
Answer: (A) Magnetic field lines are the imaginary lines drawn around a magnet which describe the magnetic field around a magnet and indicate the direction in which a hypothetical North pole would move if placed at that point.

The direction of magnetic field at a point in a magnetic field is determined by drawing a tangent at that point.
(B) Yes, if current is changed in coil X, a current will be induced in the coil Y. When current in coil X changes, the magnetic field associated with it also changes, thereby changing the magnetic field lines associated with the coil Y. This induces a current in coil Y by the process of electro magnetic induction.

(C) Fleming’s right hand rule:
Stretch the forefinger, the central finger and the thumb of the right hand perpendicular to each other so that the forefinger indicates the direction of the field, and the thumb is in the direction of motion of the conductor.
Then, the central finger shows the direction of current induced in the conductor.

Question: (A) Name and state the rule to determine the direction of force experienced by
a current carrying straight conductor placed in a uniform magnetic field which is perpendicular to it.
(B) Draw a labelled diagram of an electric motor.
Answer: (A) The rule is Fleming’s Left Hand Rule.
Statement: Stretch the forefinger, the central finger and the thumb of your left hand mutually perpendicular to each other.
If the forefinger points towards the direction of the field and the central finger that of the current, then the thumb will point towards the direction of motion of the conductor, i.e.,force.
(B) Diagram of electric motor

Question: A coil of insulated copper wire is connected to a galvanometer. What would happen if a strong bar magnet is
(A) pushed into the coil?
(B) withdrawn from inside the coil?
(C) held stationary inside the coil?
Give justification for each observation.
Answer: (A) When a strong bar magnet is pushed into a coil of insulated copper wire connected to a galvanometer, we will observe a deflection in the galvanometer in one direction.
This is because current is induced in the coil in a particular direction (either clockwise or anti clockwise) due to an increasing magnetic field. This phenomenon is called electromagnetic induction.
(B) When the magnet is withdrawn from the coil, we will again observe a deflection in the galvanometer but in direction opposite to that observed in (A).
This is because current is again induced in the coil but in an opposite direction due to a decreasing magnetic field.
(C) No deflection will be observed when the coil is held stationary as no current will be induced since magnetic field is not changing.

Question: (A) What is an electromagnet? List any two uses.
(B) Draw a labelled diagram to show how an electromagnet is made.
(C) State the purpose of soft iron core used in making an electromagnet.
(D) List two ways of increasing the strength of an electromagnet if the material of the electromagnet is fixed.
Answer: (A) An electromagnet is a temporary strong magnet. Its magnetism is only for the duration of current passing through it. The polarity and strength of an electromagnet can be changed. Uses of electromagnet-
Electromagnets are used:
(1) in electrical appliances like electric bell, electric fan etc.
(2) in electric motors and generators.
(3) in radios, television, microphone etc.
(4) in separating iron from non-magnetic material.
(5) in magnetising steel bars. (Any two)
(B)

(C) Soft iron increases the strength of the electromagnet.  (D) Ways of increasing the strength of an electromagnet:(1) If we increase the number of turns in the coil, the strength of lectromagnet increases.
(2) If the current in the coil is increased, the strength of electromagnet increases.

Question: What is a solenoid? Draw the pattern of magnetic field lines of (1) a current carrying solenoid and (2) a bar magnet. List two distinguishing feature between the two fields.
A solenoid is a coil of many circular turns of wire wrapped in the shape of a cylinder. The magnetic field produced by a solenoid is very similar to that of a bar magnet and is uniform inside the solenoid.
(1) Diagram showing pattern of field lines of a current carrying solenoid:

(2) Diagram showing pattern of field lines of a bar magnet:

Distinguishing features between the above  types of fields:

(A) What is solenoid? Draw field lines of the magnetic field through and around a current-carrying solenoid.
(B) If field lines of a magnetic field are crossed at a point, what does it indicate?
Answer: (A) Solenoid: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid.
Magnetic field around a current carrying solenoid is shown in the figure.
These appear to be similar to that of a bar magnet. One end of the solenoid
behaves like North Pole and the other end behaves like the South Pole. Magnetic field lines inside the solenoid are in the form of parallel straight lines. This means that the field is same at all the points inside the solenoid.

(B) No two field-lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible

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