CBSE Class 10 Science HOTs Magnetic Effects of Electric Current Set 03

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

Question. The pattern of the magnetic field produced by the straight current carrying conducting wire is
(a) in the direction opposite to the current
(b) in the direction parallel to the wire
(c) circular around the wire
(d) in the same direction of current
Answer: (c) circular around the wire

Question. How can you show that the magnetic field produced by a given electric current in the wire decreases as the distance from the wire increases?
Answer: This can be shown by placing a magnetic compass at varying distances from a current-carrying wire. The deflection of the compass needle is maximum when it is close to the wire and decreases as the compass is moved further away, indicating that the magnetic field strength decreases with distance.

Question. A student performs an experiment to study the magnetic effect of current around a current carrying straight conductor with the help of a magnetic compass. He reports that
I. The degree of deflection of the magnetic compass increases when the compass is moved away from the conductor.
II. The degree of deflection of the magnetic compass increases when the current through the conductor is increased.
Which of the above two observations of the student appears to be wrong and why?
Answer: Observation I is wrong. The magnetic field strength produced by a straight current-carrying wire is inversely proportional to the distance from the wire. Therefore, the degree of deflection should decrease as the compass is moved away from the conductor.

Magnetic Field due to a Current Carrying Circular Loop

Question. The nature of magnetic field line passing through the centre of current carrying circular loop is
(a) circular
(b) ellipse
(c) parabolic
(d) straight line
Answer: (d) straight line

Question. Every section of the current carrying circular loop contributes to the magnetic field lines within the loop is in the
(a) same direction
(b) opposite direction
(c) into the page
(d) out of the page
Answer: (a) same direction

Question. If the radius of a current carrying circular loop is doubled keeping all other factors remain same, then the magnetic field at the centre of the loop becomes
(a) remains same
(b) twice the original
(c) half the original
(d) thrice the original
Answer: (c) half the original

Question. Current flows in a circular loop appears to be anticlockwise, the magnetic polarity of that face is
(a) East
(b) West
(c) North
(d) South
Answer: (c) North

Question. Which of the following correctly describes the magnetic field lines within the current carrying circular loop?
(a) Outwards magnetic field.
(b) Converging magnetic field lines as we move away from the centre of the loop.
(c) Diverging magnetic field lines as we move away from the centre of the loop.
(d) All of the options
Answer: (c) Diverging magnetic field lines as we move away from the centre of the loop.

Question. Magnetic field produced by a current carrying circular wire at its centre is
(a) directly proportional to the current flowing through it.
(b) directly proportional to the number of turns of the coil.
(c) inversely proportional to radius of the coil.
(d) All of the options
Answer: (d) All of the options

Question. How will the magnetic field produced at a point due to a current carrying circular coil change if we:
(a) increase the current flowing through the coil?
(b) reverse direction of current through the coil?
(c) increase the number of turns in the coil?
Answer: Magnetic field (B) at the centre of the circular coil
(a) increases if the current is increased as \( B \propto I \)
(b) reverses on reversing the current.
(c) increases if the number of turns in the coil increases as field is directly proportional to the number of turns.

Question. There is a current carrying circular coil having \( n \) turns. The field produced at its centre is __________ times as that produced by a single turn.
(a) \( n/2 \)
(b) \( 2n \)
(c) \( n \)
(d) \( n^2 \)
Answer: (c) \( n \)

Question. The ratio of the strength of the magnetic field due to current carrying loop if the magnitude of the current through the loop is doubled is
(a) 1 : 2
(b) 2 : 1
(c) 4 : 1
(d) 1 : 4
Answer: (a) 1 : 2

Question. Explain with a reason whether the field will be stronger at the centre of current carrying loop or near the circumference of the loop.
Answer: The magnetic field is stronger near the circumference of the loop. This is because the magnetic field lines are most concentrated and crowded near the wire itself. At the center of the loop, the field lines from different segments of the loop are parallel and relatively more spread out compared to the region immediately adjacent to the conductor.

Question. The flow of current in a circular loop of wire creates a magnetic field at its centre. How may existence of this field be detected? State the rule which helps to predict the direction of this magnetic field.
Answer: The existence of the magnetic field can be detected by placing a small magnetic compass needle at the center of the loop; the needle will show deflection. The direction of this magnetic field can be predicted using the Right-Hand Thumb Rule or the Clock Face Rule.

Magnetic Field due to a Current in a Solenoid

Question. The strength of magnetic field of a current carrying solenoid is
(a) minimum at its ends
(b) uniform inside it at all points
(c) maximum at its centre
(d) zero at its centre
Answer: (b) uniform inside it at all points

Question. What type of energy conversion is observed in a current carrying linear solenoid? 
(a) Mechanical to Magnetic
(b) Electrical to Magnetic
(c) Electrical to Mechanical
(d) Magnetic to Mechanical
Answer: (b) Electrical to Magnetic

Question. What will happen if a soft iron bar is placed inside the solenoid? 
(a) The bar will be electrocuted resulting in short circuit.
(b) The bar will be magnetised as long as there is current in the circuit.
(c) The bar will be magnetised permanently.
(d) The bar will not be affected by any means.
Answer: (b) The bar will be magnetised as long as there is current in the circuit.

Question. The magnetic field lines produced inside the solenoid are similar to that of _________ 
(a) a bar magnet
(b) a straight current carrying conductor
(c) a circular current carrying loop
(d) electromagnet of any shape
Answer: (a) a bar magnet

Question. Polarity of a current carrying solenoid can be determined by
(a) use of compass needle
(b) Right hand thumb rule
(c) Fleming left hand rule
(d) either (a) or (b)
Answer: (d) either (a) or (b)

Question. The factors on which one magnetic field strength produced by current carrying solenoids depends are
(a) magnitude of current
(b) number of turns
(c) nature of core material
(d) all of the options
Answer: (d) all of the options

Question. A soft iron bar is introduced inside the current carrying solenoid. The magnetic field inside the solenoid
(a) will decrease
(b) will remains same
(c) will increase
(d) will become zero
Answer: (c) will increase

Question. If the direction of current in a solenoid, when viewed from a particular end, is clockwise, then this end of the solenoid will be:
(a) North pole
(b) East pole
(c) West pole
(d) South pole
Answer: (d) South pole

Question. The front face towards the observer of a current carrying solenoid behaves like a north pole. The direction of current in this face is
(a) clockwise
(b) anticlockwise
(c) upwards
(d) downwards
Answer: (b) anticlockwise

Question. The pattern of magnetic field lines around a current carrying solenoids resemble with the pattern of magnetic field lines
(a) around current carrying straight conductor.
(b) around a bar magnet.
(c) by a current carrying circular coil.
(d) between two magnets facing like poles one-another.
Answer: (b) around a bar magnet.

Question. The important features(s) of magnetic field inside the current carrying solenoid is/are
(a) highly uniform.
(b) same in strength at all points.
(c) in the same direction at all points.
(d) all of the options
Answer: (d) all of the options

Question. What does the divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate?
Answer: The divergence of magnetic field lines near the ends of a current carrying straight solenoid indicate the decrease in strength of magnetic field near and beyond the ends of the solenoid.

Question. What is the purpose of the soft iron core used in making an electromagnet? How is it different from the permanent magnet?
Answer: The purpose of soft iron core used in making an electromagnet that

• It loses all its magnetic property, i.e. magnetism immediately when current in the solenoid is switched off.
• It increases the magnetic field strength of an electromagnet.

It is different from the permanent magnet in the following way:
(i) Electromagnet can be demagnetised by stopping the current flowing through the solenoid while permanent magnet cannot be demagnetised easily.
(ii) Strength of magnetic field produced by electromagnet can be changed by changing the magnitude of electric current through the solenoid while strength of magnetic field of a permanent magnet cannot be changed.
(iii) The polarities of the electromagnet can be interchanged by reversing the direction of current through the solenoid while the polarities of permanent magnet cannot be interchanged.
(iv) An electromagnet can easily be made more powerful then the permanent magnet. (any one)

Question. How does the strength of the magnetic field produced by a current carrying solenoid increased?
Answer: Strength of the magnetic field can be increased by:
(i) increasing the current in the coil
(ii) increasing the number of coils in the solenoid; and
(iii) using a soft iron core within the solenoid.

Question. (a) Name the material which can be used to make- (i) Permanent magnet (ii) Temporary magnet (b) State two ways by which the strength of an electromagnet can be increased.
Answer: (a) Material which can be used to make
(i) Permanent magnet – steel, alloys (Alnico and Nipermag)
(ii) Temporary magnet – soft iron
(b) Strength of electromagnet can be increased by
(i) increasing the number of turns per unit length of the solenoid and
(ii) increasing the magnitude of the current through the solenoid.

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?
Answer:

• No, the freely suspended current carrying solenoid always stay only in geographical North and South direction, because it behaves like a bar magnet. The one end of a solenoid behave as a magnetic North pole while the other behave as a South pole.
• If the direction of current in a freely suspended solenoid is reversed, then the polarity of its end will be interchanged and the solenoid will rotate through an angle of 180°.

Question. State the various advantages and applications of electromagnet.
Answer: Advantages of an electromagnet
1. It produces very strong magnetic field.
2. Its magnetism lasts as long as current flows through it So, it is a temporary magnet.
3. The strength of electromagnet can be controlled by varying either the number of turns or the current flowing through it.
4. Polarity of electromagnet can be interchanged by changing the direction of current flowing through the solenoid.
Applications of electromagnets
1. Electromagnets are used to separate magnetic substances from non-magnetic substances.
2. Electric cranes use the electromagnets to lift and shift heavy iron loads for loading and unloading purpose.
3. They are also used in electric bells, telephones receivers, microphones, loudspeakers, electric relay, television, etc.
4. Hospitals use electromagnets to extract iron or steel bullets from the human body.

Question. The magnetic field lines inside a current carrying solenoid is:
(a) along the axis and parallel to each other
(b) perpendicular to the axis of a solenoid
(c) non-uniform
(d) circular and do not intersect each other
Answer: (a) along the axis and parallel to each other

Question. A soft iron core is inserted inside a current-carrying solenoid. The magnetic field inside the solenoid will
(a) increase
(b) decrease
(c) remain same
(d) becomes zero
Answer: (a) increase

Question. A long solenoid carrying a current produces a magnetic field B along its axis. If the number of turns per cm is halved, then new value of the magnetic field is
(a) B
(b) 2B
(c) \( B/2 \)
(d) 4B
Answer: (c) \( B/2 \)

Question. Give reason: There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
Answer: This occurs because as the magnetic field lines exit or enter the ends of the solenoid, they spread out into the surrounding space. This spreading out indicates that the magnetic field is non-uniform and its strength is decreasing as one moves away from the core of the solenoid.

Question. What is meant by solenoid? How does a current carrying solenoid behave? Give its main use. 
Answer: A solenoid is a long coil containing a large number of close turns of insulated copper wire. When current flows through it, it behaves like a bar magnet with one end acting as a North pole and the other as a South pole. Its main use is in making electromagnets.

Question. 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 magnetic compass needle or a bar magnet?
Answer: A solenoid behaves like a magnet because the magnetic fields produced by each individual turn add up to create a strong, nearly uniform field inside and a field similar to a bar magnet outside. Yes, we can determine the poles; the North pole of a compass needle will be attracted to the South pole of the solenoid and repelled by the North pole.