CBSE Class 10 Science HOTs Magnetic Effects of Electric Current Set 02

Magnetic Field and Field Lines

Question. Magnetic effect of current was discovered by
(a) Oersted
(b) Faraday
(c) Bohr
(d) Ampere
Answer: (a) Oersted

Question. By which instrument, the presence of magnetic field be determined?
(a) Magnetic Needle
(b) Ammeter
(c) Galvanometer
(d) Voltmeter
Answer: (a) Magnetic Needle

Question. The needle of magnetic compass indicates the direction of
(a) magnetic north at the point of earth surface.
(b) magnetic south at the point of earth surface.
(c) east.
(d) west.
Answer: (a) magnetic north at the point of earth surface.

Question. A compass needle is a/an
(a) iron piece
(b) small magnet
(c) steel bar
(d) powerful bar magnet
Answer: (b) small magnet

Question. The behaviour of compass needle in a magnetic field is
(a) to assure a position of magnetic field line.
(b) to assure the perpendicular magnetic field line.
(c) to rotate and stops in any direction.
(d) both (b) and (c)
Answer: (a) to assure a position of magnetic field line.

Question. Magnetic field is a quantity that has
(a) magnitude only
(b) direction only
(c) both direction and magnitude
(d) none of the options
Answer: (c) both direction and magnitude

Question. Relative strength of magnetic field at a point in the space surrounding the magnet is shown by the
(a) length of magnet
(b) thickness of magnet
(c) degree of closeness of the field.
(d) resistance offered by the surroundings
Answer: (c) degree of closeness of the field.

Question. Which of the following statement is not correct about the magnetic field?
(a) Magnetic field lines form a continuous closed curve.
(b) Magnetic field line do not interest each other.
(c) Direction of tangent drawn at any point on the magnetic field line curve gives the direction of magnetic field at that point.
(d) Outside the magnet, magnetic field lines go from South to North pole of the magnet.
Answer: (d) Outside the magnet, magnetic field lines go from South to North pole of the magnet.

Question. Magnetic needle is/an 
(a) isolated north pole pivoted at its centre of mass.
(b) isolated south pole pivoted at its centre of mass.
(c) ordinary needle made of soft iron and pivoted at its centre of mass.
(d) small bar magnet pivoted at its centre of mass.
Answer: (d) small bar magnet pivoted at its centre of mass.

Question. A freely suspended magnet always rests in geographically north and south direction because 
(a) the Earth has two poles.
(b) the Earth behaves as a huge magnet.
(c) the magnetic north pole of the Earth magnet is located very close to its south pole.
(d) the magnetic south pole of the Earth magnet is located very close to its south pole.
Answer: (c) the magnetic north pole of the Earth magnet is located very close to its south pole.

Question. The crowding of iron fillings at the end of a bar magnet indicates
(a) strong magnetic field at the ends of magnet.
(b) strong magnetic field at the centre of a magnet.
(c) weak magnetic field around the region of bar magnet.
(d) All of the options
Answer: (a) strong magnetic field at the ends of magnet.

Question. No two field lines are found to intersect each other. If they intersect, then at the point of intersection, the compass needle would point
(a) in two different directions which is possible.
(b) in two different directions which is not possible.
(c) in a particular direction.
(d) nowhere
Answer: (b) in two different directions which is not possible.

Question. After drawing the magnetic field lines around the bar magnet with the help of a compass needle, a student writes the following statements:
I. Symmetrical magnetic field lines pattern is obtained on both the sides of bar magnet.
II. The field lines around the bar magnet follow the pattern of iron filling around the magnet.
III. Deflection increases as the needle is moved towards the pole of a bar magnet.
IV. At the poles of a bar magnet, opposite poles of a compass needle comes to rest.
Choose which of the following would be correct statement(s).
(a) only III and IV
(b) I, III and IV
(c) I, II and III
(d) All four statements
Answer: (d) All four statements

Question. Equidistance parallel magnetic field lines indicate:
(a) Uniform magnetic field.
(b) Non-uniform magnetic field.
(c) Both (a) and (b).
(d) Uniform electric field.
Answer: (a) Uniform magnetic field.

Question. How can you find the direction of magnetic field from a magnetic field line?
(a) Perpendicular to the tangent drawn at that point.
(b) Along the tangent at any point of the field line.
(c) Along parallel to the field line.
(d) Using Right Hand Thumb rule.
Answer: (b) Along the tangent at any point of the field line.

Question. A piece of material that has both attractive and directive properties is called __________.
(a) magnet
(b) iron fillings
(c) resistor
(d) coil (inductor)
Answer: (a) magnet

Question. A bar magnet is cut into two pieces along its length. Which of the following statement is true?
(a) Two new bar magnets are created with half of pole strength.
(b) Two new bar magnets are created with double pole strength.
(c) Bar magnet is demagnetized.
(d) The one part created magnetic field while other created electric field.
Answer: (a) Two new bar magnets are created with half of pole strength.

Question. Right hand thumb rule is used to determine the
(a) direction of magnetic field.
(b) strength of magnetic field.
(c) direction of magnetic force.
(d) direction of induced current.
Answer: (a) direction of magnetic field.

Question. Which of the following process will produce new magnetic poles?
(a) Cutting a bar magnet in two pieces.
(b) Current through a solenoid.
(c) Placing an iron needle in contact with a magnet.
(d) All of the options
Answer: (d) All of the options

Very Short Answer Type Questions

Question. "Magnetic field is a physical quantity that has both direction and magnitude". How can this statement be proved with the help of a magnetic field lines of a bar magnet? 
Answer: We observe the following two facts about the magnetic field lines of a bar magnet which proves the required statement. These are:
(i) Field lines emerge from the north pole and merge at south pole. The deflection in the north pole of compass needle shows that inside the magnet field lines move from south pole to north pole of the bar magnet.
(ii) The relative strength of the magnetic field is shown by the degree of closeness of the field lines. Crowded are the field lines, stronger is the field.

Short Answer Type Questions

Question. Define magnetic field. What are magnetic field lines? Justify the following statements
(a) Two magnetic field lines never intersect each other. 
(b) Magnetic field lines are closed curves. 
Answer: Magnetic field: It is the region around a magnetic material such as bar magnet or moving electric charge within which the magnetic force acts.
Magnetic field lines: It is defined as the path along which the unit North pole (imaginary) tends to move in a magnetic field if free to do so.
By drawing a tangent at that point on the magnetic field lines one can find the direction of magnetic field at that point.
(a) The magnetic lines of force do not intersect (or cross) one another. If they do so then at the point of intersection, two drawn tangents at that point indicate that there will be two different directions of the same magnetic field, i.e. the compass needle points in two different directions which is not possible.
(b) Magnetic field lines are closed continuous curves. They emerge out from the north pole of a bar magnet and go into its south pole. Inside the magnet they move from south pole to north pole.

Question. A student dipped a bar magnet in a heap of iron fillings and pulled it out. He found that iron fillings got stuck to the magnet.
(a) Which regions of the magnet have more iron fillings sticking to it? What are these regions called?
(b) What conclusion would you like to draw from the amount of iron fillings clinging to these regions?
Answer: (a) • The ends of the magnet have more amount of iron fillings sticking to it as compared to middle part of the bar magnet. It is because the magnetic strength is maximum at the end and minimum at the middle of the magnet.
• These regions are called pole of the bar magnet.
(b) Equal magnetic strength of each pole is indicated by the equal amount of iron fillings clinging to them.

Question. A student fixes a white sheet of paper on a drawing board. He places a bar magnet in the centre and sprinkles some iron filings uniformly around the bar magnet. Then he taps gently and observes that iron filings arrange themselves in a certain pattern.
(a) Why do iron filings arrange themselves in a particular pattern?
(b) Which physical quantity is indicated by the pattern of field lines around the bar magnet?
(c) State any two properties of magnetic field lines. 
Answer: (a) When iron filings are placed in a magnetic field around a bar magnet, they behave like tiny magnets. The magnetic force experienced by these tiny magnets make them rotate and align themselves along the direction of field lines. 
(b) The physical property indicated by this arrangement is the magnetic field produced by the bar magnet.
(c) Magnetic field lines never intersect, magnetic field lines are closed curves. 

QUESTIONS

Question. Choose the incorrect statement from the following regarding magnetic lines of field
(a) The direction of magnetic field at a point is taken to be the direction in which the north pole of a magnetic compass needle points.
(b) Magnetic field lines are closed curves.
(c) If magnetic field lines are parallel and equidistant, they represent zero field strength.
(d) Relative strength of magnetic field is shown by the degree of closeness of the field lines.
Answer: (c) If magnetic field lines are parallel and equidistant, they represent zero field strength.

Question. The SI unit of magnetic field intensity is
(a) Gauss
(b) Torr
(c) Tesla
(d) Newton
Answer: (c) Tesla

Question. According to Right-hand thumb rule, the thumb indicates the direction of
(a) magnetic field
(b) electric current
(c) magnetic force
(d) motion of the conductor
Answer: (b) electric current

Magnetic Effects of Electric Current

Question. When a current flows through a straight conductor, a magnetic field is produced around it. Consider the following statements about this field:
I. The direction of the magnetic field of a current carrying straight conductor is determined by right-hand thumb rule.
II. A charged body placed in this field experiences a force whose direction is given by Fleming’s left hand rule.
III. The magnetic field lines around a current carrying straight conductor are in the form of concentric circles with the conductor as the centre.
The correct statement(s) is/are: 
(a) I only
(b) III only
(c) I and II
(d) I and III
Answer: (d) I and III

Question. The strength of magnetic field around a current carrying conductor is
(a) inversely proportional to the current but directly proportional to the square of the distance from wire.
(b) directly proportional to the current and inversely proportional to the distance from wire.
(c) directly proportional to the distance and inversely proportional to the current.
(d) directly proportional to the current but inversely proportional the square of the distance from wire.
Answer: (b) directly proportional to the current and inversely proportional to the distance from wire.

Question. A current through a horizontal power line flows from south to North direction. The direction of magnetic field line 0.5 m above it is towards
(a) North
(b) South
(c) West
(d) East
Answer: (d) East

Question. Who has stated the Right hand Thumb Rule?
(a) Orsted
(b) Fleming
(c) Einstein
(d) Maxwell
Answer: (d) Maxwell

Question. The magnetic field at a point due to current carrying conductor is directly proportional to
(a) resistance of the conductor.
(b) current flowing through the conductor.
(c) voltage applied across the conductor.
(d) distance of the point from the conductor.
Answer: (b) current flowing through the conductor.

Question. Oersted experiment prove that when an electric current is passed through a conducting wire, a _________ is produced around it.
(a) Electric field
(b) Magnetic field
(c) Heat
(d) Light
Answer: (b) Magnetic field

Question. Right hand thumb rule is used to determine the
(a) direction of magnetic field.
(b) strength of magnetic field.
(c) direction of magnetic force.
(d) direction of induced current.
Answer: (a) direction of magnetic field.

Question. Suppose a horseshoe magnet is held vertically upwards with the North Pole is on left. A wire passing between the poles carries a direct current directed away from you. In what direction is the magnetic force exert on the wire?
(a) Downward
(b) Upward
(c) Towards East
(d) Towards South
Answer: (a) Downward

Question. The resultant magnetic field at point ‘P’ situated midway between two parallel wires (placed horizontally) each carrying a steady current I is 
(a) in the same direction as the current in the wires.
(b) in the vertically upward direction.
(c) zero
(d) in the vertically downward direction.
Answer: (c) zero

Very Short Answer Type Questions 

Question. The magnetic field associated with a current carrying straight conductor is in anticlockwise direction. If the conductor was held along the east-west direction, what will be the direction of current through it? Name and state the rule applied to determine the direction of current.
Answer: Direction of current – east to west is determined by Right-hand thumb rule.
Right-Hand Thumb Rule : If we hold a current carrying conductor by right hand in such a way that the stretched thumb is along the direction of current, then the curly fingers around the conductor represents the direction of field lines of magnetic field.

Question. A compass needle is placed near a current-carrying wire. State your observation for the following cases, and give reason for the same in each case -
(a) Magnitude of electric current in the wire is increased.
(b) The compass needle is displaced away from the wire. 
Answer: (a) Observation: Deflection of the needle increases
Reason: Magnetic field strength due to current carrying wire increases as current in the wire increases, i.e. \( B \propto I \).
(b) Observation: The deflection in the compass needle decreases as its displacement from the current - carrying wire increases.
Reason: Strength of magnetic field reduces with the increase in distance from the wire as \( B \propto \frac{1}{r} \).

Question. A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor. He reports that
(a) for a given battery, the degree of deflection of a N-pole decreases when the compass is kept at a point farther away from the conductor.
(b) the direction of deflection of the north pole of a compass needle kept at a given point near the conductor remains unaffected even when the terminals of the same battery sending current in the wire are interchanged.
Which of the above observations of the student appears to be wrong and why? 
Answer: (a) The first observation is correct because the strength of magnetic field decreases with the increase in distance. As a result, degree of deflection of a N-pole of a compass needle decreases.
(b) Second observation is incorrect because if the direction of current is reversed, the direction of field lines will also be reversed. So, north pole of the magnetic compass needle will be directed in the opposite direction.

Question. How is the strength of magnetic field near a straight current-conductor
(a) related to the strength of current in the conductor? 
(b) is affected by changing the direction of flow of current in the conductor?
Answer: (a) The strength of magnetic field around a straight current conductor increases on increasing the strength of current in the conductor or vice versa.
(b) The direction of magnetic field around a straight current carrying conductor gets reversed if the direction of current through that conductor is reversed.

Question. (a) A compass needle gets deflected when brought near a current carrying conductor. Why?
(b) What happens to the deflection of the needle when current in the conductor is increased?
Answer: (a) The current carrying conductor produces a magnetic field around it. This magnetic field exerts a force on the magnetic needle of compass. As a result, compass needle gets deflected.
(b) When the current in the conductor increases, the magnitude of magnetic field produced around it increases and consequently, the deflection in the compass needle increases.