Chapter 12. Magnetic Effects of Electric Current

Class 10 Science Chapter 12. Magnetic Effects of Electric Current Questions and Answers :

Previous Years Questions 2008

Question: Why is a series arrangement not used for connecting domestic electrical appliances in a circuit ?[1M]

Answer: A series arrangement is not used for domestic appliances because if one appliance fails, the entire circuit is broken, disrupting power to all devices, making it less reliable.

Question: What is meant by the term, ‘magnetic field’ ? Why does a compass needle show deflection when brought near a bar magnet ? [2M]

Answer: A magnetic field is the region around a magnet where magnetic forces can be experienced by another magnet or a magnetic material.

A compass needle shows deflection when brought near a bar magnet because the needle itself is a small magnet. The magnetic field of the bar magnet exerts a force on the needle, aligning it along the field lines.

Question: (a) Distinguish between the terms ‘overloading’ and ‘short-circuiting’ as used in domestic circuits .

(b) Why are the coils of electric toasters made of any alloy rather than a pure metal ? [3M]

Answer: (a) Distinguishing Overloading and Short-Circuiting are:

Overloading: Occurs when excessive current flows through a circuit due to too many appliances being used simultaneously, exceeding the circuit's capacity.

Short-Circuiting: Happens when the live wire comes in direct contact with the neutral wire, creating a low-resistance path and causing a sudden surge in current.

(b) The coils of electric toasters are made of an alloy rather than a pure metal because:

(i) Alloys have higher resistivity, generating more heat for a given current.

(ii) They have a higher melting point, making them less likely to melt at high temperatures.

(iii) Alloys are more durable and resist oxidation, ensuring longer life.

Previous Years Questions 2009

Question: (a) What is a magnetic field ? How can the direction of magnetic field lines at a placed be determined ?

(b) State the rule for the direction of the magnetic field produced around a current carrying conductor . Draw sketch of the pattern of field lines due to a current flowing through a straight conductor . [5M]

Answer: (a) A magnetic field is the region around a magnet where magnetic forces can be experienced by another magnet or a magnetic material.

The direction of magnetic field lines at a place can be determined using a compass needle. The needle aligns itself along the field lines, pointing in the direction of the magnetic field.

(b) The Right-Hand Thumb Rule states: If we hold a current-carrying straight conductor in our right hand, with the thumb pointing in the direction of the current, then the direction in which the fingers wrap around the conductor represents the direction of the magnetic field lines.

Sketch of Field Lines Around a Straight Conductor:

 

Question: (a) What is a solenoid ? Draw a sketch of the pattern of field lines of the magnetic field through and around a current carrying solenoid .

(b) 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 .  [2009 , 2010 5M]

Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. Solenoids are widely used in electromechanical devices, such as electromagnets, inductors, and transformers.

Pattern of Magnetic Field Lines in a Solenoid:

Inside the solenoid: The field lines are nearly parallel, indicating a strong and uniform magnetic field.

Outside the solenoid: The field lines spread out and are non-uniform, resembling the field lines of a bar magnet.

(b) Consider a circular loop of wire lying flat in the plane of the table. If the current flows clockwise through the loop:

Inside the loop: By applying the right-hand rule, point your thumb in the direction of the current. The fingers curl in the direction of the magnetic field. For a clockwise current, the field inside the loop points downward, perpendicular to the plane of the loop.

Outside the loop: The field lines curve outward and eventually loop back into the opposite side.

Previous Years Questions 2010

Question: A charged particle enters at right angles into a uniform magnetic field is shown . What should be the nature of charge on the particle if it begins to move in a direction pointing vertically out of the page due to its interaction with the magnetic field ? [1M]

Answer: The particle must be positively charged. According to the right-hand rule, if the magnetic field points into the page and the force is upward, the charge is positive.

Question: A coil of insulated wire is connected to a galvanometer . What would be seen if a bar magnetic with its north pole towards one face of the coil is :

(i) Moved quickly towards it ,  (ii) Moved quickly away from the coil and (iii) Placed near its one face ? Name the phenomena involved . [2010 2M]  (Ignore)

Answer: (i) The galvanometer needle deflects, indicating a current is induced in the coil. The direction of the current is such that it opposes the motion of the bar magnet.

(ii) The galvanometer needle deflects in the opposite direction, indicating a current is induced in the opposite direction. This current again opposes the motion of the bar magnet.

(iii) No deflection is observed in the galvanometer. This is because there is no relative motion between the magnet and the coil, so no change in the magnetic flux occurs.

The phenomenon involved is electromagnetic induction, where a change in magnetic flux through a coil induces an electric current in the coil.

Previous Years Questions 2019

Q13. What is a solenoid ? Draw the pattern of magnetic field lines of (i) A current carrying solenoid and (ii) A bar magnet .List two distinguishing features between the two fields. [2019 5M]

Answer: A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. Solenoids are widely used in electromechanical devices, such as electromagnets, inductors, and transformers.

(i) Magnetic Field of a Current-Carrying Solenoid:

The field lines inside the solenoid are dense, parallel, and uniform, indicating a strong and uniform magnetic field.

The field lines emerge from one end (considered the north pole) and re-enter at the other end (considered the south pole), resembling a bar magnet.

(ii) Magnetic Field of a Bar Magnet:

The field lines are dense near the poles and spread out as they move away from the magnet.

They emerge from the north pole and curve around to enter the south pole, forming closed loops.

Distinguishing Features Between the Two Fields:

(a) Uniformity Inside the Field:

Solenoid: The magnetic field inside the solenoid is uniform.

Bar Magnet: The magnetic field inside a bar magnet is non-uniform.

(b) Control Over Magnetic Field:

Solenoid: The magnetic field strength can be controlled by adjusting the current or the number of turns of the coil.

Bar Magnet: The magnetic field strength is fixed and depends on the material and size of the magnet.

Question: What is the function of a galvanometer in a circuit ? [1M]

Answer: A galvanometer is used to detect and measure small electric currents by deflecting its needle in response to the current passing through the coil within its magnetic field.

Previous Years Questions 2020

Question: The Change in magnetic field lines in a coil is the cause of induced electric current in it . Name the underlying phenomenon. [1M]

Answer: The underlying phenomenon is electromagnetic induction.

Question: (a) What is an electromagnet ? List any two uses .

(b) Draw a labeled 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. [5M]

Answer: (a)  An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. It consists of a coil of wire, usually wound around a soft iron core, which becomes magnetized when current flows through the coil.

Two Uses of an Electromagnet:

In electric motors: Electromagnets are used to generate rotational motion.

In scrapyards: Electromagnets are used to lift and move heavy metal objects.

(b) Labeled Diagram of an Electromagnet:

(c) The soft iron core in an electromagnet serves to concentrate and strengthen the magnetic field produced by the current. It increases the magnet's strength and ensures that the magnetic field is confined to the core, enhancing the electromagnet's effectiveness.

(d) Two Ways of Increasing the Strength of an Electromagnet (if the material is fixed):

(i) Increase the number of turns in the coil: More turns of wire will create a stronger magnetic field.

(ii) Increase the current passing through the coil: Higher current results in a stronger magnetic field.

Previous Years Questions 2022

Question: (a) Name the poles P, Q , R and S of the magnets in the following figures ‘A’ and ‘B’ :

(b) When is the force experienced by a current carrying straight conductor placed in a uniform magnetic field. [2M]

Answer: (a) P –  North Pole.

Q –  South Pole.

R –  North Pole

S –  South Pole

(b) The force experienced by a current-carrying straight conductor in a uniform magnetic field is maximum when the conductor is perpendicular to the magnetic field and zero when it is parallel.

Question: When is the force experienced by a current carrying straight conductor placed in a uniform magnetic field .

(i) Maximum ;   (ii) Minimum ? [2022 2M]

Answer: The force experienced by a current-carrying straight conductor in a uniform magnetic field is:

(i) Maximum: When the conductor is perpendicular to the magnetic field (θ = 90°).

(ii) Minimum: When the conductor is parallel to the magnetic field (θ = 0° or θ = 180°).

Question: Case study Based Questions :

A student was asked to perform an experiment to study the force on a current carrying conductor in a magnetic field . He took a small aluminium rod AB, a strong horse shoe magnet, some connecting wires, a battery and a switch and connected them as shown . He observed that on passing current , the rood gets displaced . On reversing the direction of current, the direction of displacement also gets reversed. On the basis of your understanding of this phenomenon, answer the following questions : [4M]

 

(a) Why does the rod get displaced on passing current through it ?

(b) State the rule that determines the direction of the force on the conductor AB .

(c) (i) If the U shaped magnet is held vertically and the aluminium rod is suspended horizontally with its end B towards due north , then on passing current through the rod from B to A as shown in figure, in which direction will the rod be displaced ?

(ii) Name any two devices that use current carrying conductors and magnetic field.

Answer: (a) The rod gets displaced because a force is exerted on it due to the interaction between the magnetic field of the horseshoe magnet and the magnetic field produced by the current in the rod.

(b) The direction of the force on the conductor is determined by Fleming's Left-Hand Rule, which states that if the thumb, forefinger, and middle finger of the left hand are stretched mutually perpendicular, with the forefinger pointing in the direction of the magnetic field and the middle finger in the direction of the current, the thumb points in the direction of the force.

(c) (i) If the U-shaped magnet is held vertically and the aluminum rod is suspended horizontally with its end B towards due north, then on passing current through the rod from B to A, the rod will be displaced vertically upward or downward, depending on the polarity of the magnet.

(ii) Two devices that use current-carrying conductors and magnetic fields are:

(A) Electric Motor     (B) Loudspeaker

Question: Draw the pattern of magnetic field lines produced around a current carrying straight conductor held vertically direction of the field lines as well as the direction of current flowing through the conductor .

Answer: To draw the magnetic field lines around a current-carrying straight vertical conductor:

Magnetic Field Pattern: The field lines form concentric circles around the conductor.

Direction of Field: Use the Right-Hand Thumb Rule: If the thumb points in the current's direction, curled fingers indicate the magnetic field's direction.

[ Explanation: For upward current flow, the magnetic field is counterclockwise; for downward current, it is clockwise.]

Question: A student fixes a sheet of white paper on a drawing board using some adhesive materials. She places a bar magnet in the centre of it and sprinkles some iron filings uniformly around the bar magnet using a salt-sprinkler. On tapping the board gently, she observes that the iron filings have arranged themselves in a particular pattern.

(a) Draw a diagram to show this pattern of iron filings. [1M]

(b) Draw the magnetic field lines of a bar magnet showing the poles of the bar magnet as well as the direction of the magnetic field lines. [1M]

(c) (i) How is the direction of magnetic field at a point determined using the field lines ? Why do two magnetic field lines not cross each other ? [2M]

OR

(ii) How are the magnetic field lines of a bar magnet drawn using a small compass needle ? Draw one magnetic field line each on both sides of the magnet. [2M]

Answer: (a) Diagram of Iron Filings Pattern:

Sprinkling iron filings around the bar magnet and tapping gently results in a pattern showing the magnetic field lines. These lines originate at the north pole and curve around to enter the south pole. The filings are denser near the poles, indicating stronger magnetic fields.

(b) Magnetic Field Lines of a Bar Magnet:

The magnetic field lines around a bar magnet are closed loops. They:

(i) Start from the north pole and enter the south pole outside the magnet.

(ii) Continue through the magnet from the south pole to the north pole inside.

(c) (i) Direction of Magnetic Field Using Field Lines
The direction of the magnetic field at any point is tangent to the field line at that point. A small compass needle aligns along this tangent.
If two field lines crossed, it would imply two directions of the magnetic field at a single point, which is impossible.

OR

(ii) To draw field lines:

(a) Place a small compass near the magnet. The needle aligns itself with the local magnetic field.

(b) Mark the direction of the needle and move the compass to another point.

(c) Repeat to trace the field lines.

Bar magnet with a single field line drawn on each side starting from the North Pole and curving to the South Pole.