# Magnetic Effect of Electric Current Class 10 Science Exam Questions

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## Class 10 Science Exam Questions Magnetic Effect of Electric Current

Class 10 Science students should read and understand the important questions and answers provided be Magnetic Effect of Electric Current which will help them to understand all important and difficult topics.

Very Short Answer type Question :

Question. A bar magnet is placed between two iron bars. Draw a diagram to show the induced poles.
Answer: Both the iron bars get magnetised as shown in the figure

Question. Identify the poles of the magnet as shown in the given figure:

Answer: A1 represents North pole and B1 represents South pole.

Question. State the direction of magnetic field inside a bar magnet.
Answer: It is from South pole to North pole.

Question. Mention the special feature regarding the shape of magnetic field lines.
Answer: Magnetic field lines are closed curves.

Question. If magnetic field lines are crossed at a point, what does it indicate?
Answer: The magnetic lines of force do not intersect with each another due to the fact that resultant force on the north pole at any point can only be in one direction. But if the two magnetic lines of force intersect one another, then the resultant force on the north pole placed at the point of intersection will be along two directions, which is not possible.

Question. Draw a diagram to represent the uniform magnetic field in the region around the magnet.

Question. What type of core is used in electromagnets?

Question. 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: The direction of magnetic field will be perpendicular to the plane of paper inwards inside the loop and perpendicular to the plane of paper outwards from inside.

Question. What type of core is used to make electromagnets?

Question. Give the factors on which magnetic field produced by a current carrying solenoid will depend.
Answer: (i) The current through the solenoid. (ii) The number of turns in the solenoid
(iii) Nature of core on which wires are wound in solenoid.

Question. Why does a compass needle get deflected when brought near a bar magnet?
Answer: A compass needle behaves like a small bar magnet when it is brought near a bar magnet. Its magnetic field lines interact with that of bar magnet. Hence compass needle gets deflected.

Question. Define electromagnetic induction.
Answer : The production of electricity from magnetism is called electromagnetic induction.

Question. What is the function of a galvanometer in a circuit ?
Answer : Galvanometer is a device that detects the presence of current in a circuit. It is also used for measuring the amount of current in the circuit.

Question. Define a compass.
Answer : A compass is a device used to show magnetic field direction at a point. It consists of a tiny pivoted magnet usually in the form of a pointer which can turn freely in the horizontal plane.

Question. Define magnetism.
Answer : The property by virtue of which a magnet attracts certain metals such as iron, cobalt, nickel etc., is termed as magnetism.

Question. What is a permanent magnet ? Give one use of it.
Answer : A permanent magnet is a magnet made from steel such that once magnetised, it does not lose it magnetism easily.

Question. What is a solenoid ?
Answer : A solenoid is a long coil containing a large number of close turns of insulated copper wire.

Question. What is a galvanometer ?
Answer : A galvanometer is an instrument which can detect the presence of electric current in a circuit.

Question. What do you mean by ‘magnetic field’ of a magnet ?
Answer : The space or region around a magnet in which the force of attraction or repulsion due to the magnet can be detected is called the magnetic field.

Question. What is the difference between an A.C. generator and a D.C. generator ?
Answer : A.C. generator has slip rings while D.C. generator has a commutator.

Question. Define an electromagnet.
Answer : An electromagnet is a magnet consisting of a long coil of insulated copper wire wrapped around a soft iron core that is magnetised only when electric current is passed through the coil.

Question. Name the factors on which force acting on a current carrying conductor will depend.
Answer: (i) The current through the conductor. (ii) The strength of magnetic field.
(iii) The length of the conductor.

Question. State the direction of magnetic field in the following case:
Answer: Direction is out of the page.

Question. A beam of alpha particles enters a chamber moving along the magnetic field. What is the magnetic force experienced by the beam?
Answer: Zero, it is because beam is moving parallel to the magnetic field.

Question. When is the force experienced by a current carrying conductor placed in a magnetic field greatest?
Answer: When the current in the conductor flows perpendicular (90°) to the direction of the magnetic field, maximum force is generated.

Question. What is the pattern of field lines inside a solenoid? What do they indicate?
Answer: The magnetic field is in the form of parallel lines. It indicates a uniform magnetic field because magnetic field lines are parallel.

Question: A charged particle enters at right angle into a uniform magnetic field as 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?

Answer: By using Fleming’s left hand rule if the direction of motion of charged particle to be vertically out of the page, then the charged particle must be positive in nature.

Question: State the rule which gives the direction of magnetic field associated with a current carrying conductor.
Answer: Maxwell’s right hand thumb rule or corkscrew rule gives the direction of magnetic field associated with a current carrying conductor.

Question: When is the forces experienced by a current carrying conductor placed in a magnetic field the largest?
Answer: Force experienced by a current carrying conductor placed in a magnetic field is largest when the direction of current is perpendicular to the direction of magnetic field.

Question. What is an electric motor ? Name five main parts of a D.C. motor.
Answer : An electric motor is a device which converts the electrical energy into mechanical energy.
The five main parts of a D.C. motor are :
(a) Strong field magnet, (b) Armature coil,
(c) Split ring or commutator, (d) Carbon brushes, and
(e) Battery.

Question. The diagram in given figure shows a three pin socket marked as 1, 2 and 3.

(a) Identify and write live (L), neutral (N) and earth
(E) against the correct number.
(b) To which part of the appliance is the terminal 1 connected ?
Answer : (a) 1 → Earth (E), 2 → Neutral (N) and 3 → Live (L).
(b) Terminal 1 is connected to the metal body of the appliance.

Question. State Fleming’s right hand rule.
Answer : It states that, “Stretch your right hand in such a way that the first finger, the central finger and the thumb are mutually perpendicular to each other. If the first finger points along the direction of magnetic field and the thumb points along the direction of motion of the conductor, then the direction of induced current is given by the direction of the central finger.”

This rule is also called dynamo rule.

Question. Give reasons for the following :
(i) There is either a convergence or a divergence of magnetic field lines near the ends of a current carrying straight solenoid.
(ii) The current carrying solenoid when suspended freely rests along a particular direction.
(iii) The burnt out fuse should be replaced by another fuse of identical rating.
(i) When a current pass through solenoid, it creates a
nearly uniform magnetic field inside or along the axis of the solenoid. Outside the coil or solenoid, i.e., at the ends and beyond the magnetic field is small and appears to diverge. This divergence is because the distance from the current carrying solenoid increases. The distance from the current carrying conductor and the magnetic field are inversely proportional i.e., as distance increases, magnetic field strength decreases.
(ii) The current carrying solenoid when suspended freely rests along a particular direction because it behaves like a bar magnet.
(iii) Fuse is the most important safety device, used for protecting the circuits due to short-circuiting or overloading of the circuits. A fuse wire works because of its lower melting point which is possible. If a fuse with larger rating is used with an appliance, the fuse wire shall not melt and hence would fail to serve the required purpose.

Question. (a) What is an electric generator ?
(b) Name and state the principle on which it works.
(c) Name two types of generators.
Answer : (a) An electric generator is a device which is used to convert mechanical energy into electrical energy.
(b) It works on the principle of electromagnetic induction which states that, “when a straight conductor is moved in a magnetic field, then a current is induced in it.”
(c) The two types of generators :
(i) A.C. generator, (ii) D.C. generator.

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.
(c) Current induced in a coil due to its rotation in a magnetic field.
Answer : (a) Right hand thumb rule or Maxwell’s Corkscrew rule.
(b) Fleming’s left hand rule.
(c) Fleming’s right hand rule.

Question. The diagram shows a current carrying coil passing through a cardboard sheet. Draw three magnetic lines of force on the board. State two factors on which magnitude of magnetic field at the centre depends.

Figure shows the magnetic lines of force due to current carrying coil.
The magnitude of magnetic field at the centre of coil depend on :
(a) the strength of current in the coil, and
(b) the number of turns in the coil.

Question. AB is a current carrying conductor in the plane of the paper as shown in figure. What are the directions of magnetic fields produced by it at points P and Q ?
Given r1 > r2, where will the strength of the magnetic field be larger ?
Answer : Since the direction of the current in the current carrying conductor AB is upwards, the direction of the magnetic field would be anti-clockwise as deduced by applying right hand thumb rule. Consequently, the magnetic field at point P would be towards the plane  and, at point Q, the direction of the magnetic field would be away fromthe plane.

Since the strength of the magnetic field is inversely proportional to the distance (r), the field at P would be weaker as compared to Q [·.· r1 > r2].

Question. In the diagram XY is a straight conductor carrying current in the direction marked by the arrow. The conductor is held vertical by passing it through a horizontal cardboard sheet. Draw three magnetic lines of force on the board and mark the direction of magnetic field in your diagram. State two factors on which magnitude of magnetic field at a point, depends.

Answer : The magnetic lines of force due to current in the straight conductor XY are shown in the figure given below.
The arrows on the magnetic lines of force shows the direction of magnetic field.
The magnitude of magnetic field at a point depends on :
(a) The strength of current in the conductor, and
(b) The distance of point from the conductor.

Question. What do you mean by : (a) Direct Current (D.C.) and
(b) Alternating Current (A.C.)
Answer : (a) An electric current whose magnitude is either constant or variable, but the direction of flow in a conductor remains the same, is called direct current.
(b) An electric current whose magnitude changes with time and direction reverses periodically, is called an alternating current.

Question. Identify the type of magnetic field represented by the magnetic field lines given below and name the type of conductors which can produce them.
Answer: (a) These magnetic field lines are produced by a current carrying loop.
(b) These are magnetic field lines produced by solenoid.

Question. Define a solenoid. Compare the magnetic field produced by a solenoid with that of a bar magnet.
Answer: A coil of many circular turns of copper wire wrapped in the shape of a cylinder, is called a solenoid.
The magnetic field lines in a solenoid, through which current is passed, is very similar to that of a bar magnet. One end of the coil acts like the magnetic north pole, while the other acts like the magnetic south pole. The magnetic field produced by a long solenoid has all the properties of the field produced by a bar magnet.

Question. How will the magnetic field produced at a point due to a current carrying circular coil change if we:
(i) increase the current flowing through the coil, (ii) reverse direction of current through coil,
(iii) increase the number of turns in the coil?
Answer: (i) The strength of magnetic field will increase. (∴ B ∝ I)
(ii) The direction of magnetic field will be reversed.
(iii) The magnetic field produced will increase because magnetic field produced is directly proportional to the number of turns in the coil.

Question. How is the strength of magnetic field near a straight current-carrying conductor
(i) related to the strength of current in the conductor?
(ii) is affected when the direction of flow of current is reversed?
Answer: (i) The strength of magnetic field is directly proportional to the strength of current.
(ii) If we reverse the direction of current, the direction of magnetic field will also be reversed.

Question. State two ways by which the strength of an electromagnet is increased.
Answer: (i) Increase in number of turns in the solenoid.
(ii) Increase in the strength of current flowing in 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? Explain.
Answer: A current carrying solenoid behaves like a bar magnet. When it is suspended freely it will stay in north–south direction. On reversing the direction current, it will turn to 180°° because its polarity will be reversed.

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: The compass needle is deflected more.
Reason: Current carrying wire produces magnetic field, (B ∝ I).
(b) Observation: The deflection of magnetic needle decreases.
Reason: The strength of magnetic field decreases with increase in distance from the wire. (B ∝ I/d)

Question. (a) Two magnets are lying side by side as shown below. Draw magnetic field lines between the poles P and Q:
(b) What does the degree of closeness of magnetic field lines near the poles signify?
Answer: (a) Magnetic field lines are shown below:

(b) It shows that magnetic field is stronger near the poles, i.e. the pole of another magnet when placed in the magnetic field of a magnet will experience greater force. That is why field lines are crowded.

Question. Magnetic field lines of two magnets are shown in figure A and figure B.

Select the figure that represents the correct pattern of field lines. Give reasons for your answer. Also name the poles of the magnets facing each other.
Answer: Figure ‘B’ represents correct pattern of magnetic field lines because magnetic field lines never intersect each other. If these intersect there will be two directions of the magnetic field at the point of intersection, which is not possible. In figure B. field lines are emerging (going away) from the magnet, so both the poles are north poles.

Question. Identify the poles of the magnet in the given figure (1) and (2).

Answer: Field lines emerge from North pole and merge at South pole (S). So, X represents North pole and Y represents South pole.

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: When the observer observes the direction of magnetic field from west then the direction of current is from east to west and if observer is at east side then the direction of current is from west to east.
Right hand thumb rule: If we hold a current carrying conductor in our right hand in a such a way that stretched thumb is along the direction of the current, then curls of fingers around the conductor represents the direction of magnetic field lines.

Question. Draw magnetic field lines around a bar magnet.

Question. What are magnetic field lines? Explain why magnetic field lines are closed curves?
Answer: The closed path traced by the unit North pole (imaginary) in a magnetic field are called magnetic field lines.
They are continuous closed curves because they diverge from the north pole of a bar magnet and converge to its south pole.

Question. Describe an activity to determine the direction of magnetic field produced by a current carrying straight conductor. Also show that the direction if the magnetic field is reversed on reversing the direction of the current.
Answer: (i) Take a straight vertical wire AB passing through a horizontal cardboard ‘C’.

(ii) The ends of wires are connected to a battery and a switch.
(iii) When the current is passed through the wire AB, it produces a magnetic field around it, which can be shown by sprinkling iron filings on the cardboard ‘C’.
(iv) The iron filings get magnetised and arrange themselves in concentric circles around the wire.
(v) It shows that magnetic field of lines are circular in nature.
(vi) When current passed in the wire it flows in upward direction, the lines of force are in anticlockwise direction.
(vii) Now pass current from B to A, i.e. in downward direction, the magnetic lines of force will be clockwise.

Question. (a) Draw magnetic field lines of a current carrying circular loop. Identify the region where field is strongest and why?
(b) List two properties of magnetic field lines.
Answer: (a) On observing the field lines, it shows that magnetic field due to the current carrying circular loop is maximum and normal to the current carrying loop at its center because magnetic field due to each part of loop adds up.
(b) (i) No two magnetic field lines intersect with each other at any point.
(ii) More crowded field lines means a stronger magnetic field.

Question. Why and when does a current carrying conductor kept in magnetic field experiences force? List the factors on which direction of force will depend.
Answer: The movement of electrons takes place in the conductor in a particular direction when current is passed through it. These charged particles are moving in the magnetic field which experiences force.
The current carrying conductor has its own magnetic field, when it superimpose the magnetic field of magnet. Due to this, current carrying conducter experiences a force. Thus conductor experiences a force when placed in a uniform magnetic field.
Factors on which direction of force depends:
(i) The direction of force depends upon the direction of magnetic field.
(ii) It also depends upon the direction of current flowing through the conductor.

Question. A uniform magnetic field is directed vertically upwards. In which direction in this field forces an particle (+ve charged) be projected to that it is deflected southward? Name and state the rule you have to use to find the direction in this force.
Answer: The direction of motion of particles is from west to east. Fleming’s left hand rule is used to find the direction of force.

Question. For the circular coil carrying current shown below draw magnetic field lines. Decide which of its face behaves as north pole and which face behaves as south pole. Give reason to justify your answer.

Answer: Front face behaves like a north pole as field emerges out of it. Rear face behaves as south pole as field enters into this face.

Question. The given magnet is divided into three parts A, B and C as:
Name the part when the strength of magnetic field is (i) maximum, (ii) minimum. How will the density of magnetic field lines differ at these parts?
Answer: (i) Maximum of magnetic field strength is at ‘A’ and ‘C’
(ii) Minimum of magnetic field strength is at ‘B’.
At ‘A’ and ‘C’ magnetic field lines are crowded whereas these are spread out at ‘B’.

Question. (a) In a pattern of magnetic field lines due to bar magnet, how can the regions of relative strength be identified?
(b) Compare the strength of magnetic field near the poles and the middle of a bar magnet.
Answer: (a) The closeness of lines measures the relative strength of magnetic field.
(b) The strength of magnetic field is highest near the poles whereas minimum in the middle of bar magnet.

Question. (i) A compass needle gets deflected when brought near a current carrying conductor. Why?
(ii) What happens to the deflection of needle when current in the conductor is increased?
Answer: (i) It is because current carrying conductor produces a magnetic field which superimposes with magnetic field of compass needle due to which needle of compass gets deflected.
(ii) The deflection in the magnetic needle will increase as the strength of current increases.

Question: Draw a diagram to show the magnetic field lines around a bar magnet. List any two properties of magnetic field lines.

(i) Magnetic field lines start from the north pole of a magnet and end at the south pole of a magnet.
(ii) Two magnetic field lines can not intersect each other.

Question: What is meant by the term, “magnetic field”? Why does a compass needle show deffection when brought near a bar magnet?
Answer: Magnetic field : It is defined as the space surrounded the magnet in which magnetic force can be experienced.
Compass needle is itself made up of tiny magnet. When it is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence needle shows deflection.

Question: What is a solenoid? Draw the pattern of magnetic field lines of a solenoid through which a steady currentflows. What does the pattern of field lines inside the solenoid indicate?
Answer: Solenoid : A coil of many circular turns of insulated copper wire wrapped in the shape of cylinder is called solenoid.

The pattern of magnetic field lines inside the solenoid indicates that the magnetic field is the same at all points inside the solenoid.That is, the field is uniform inside the solenoid.

Question. (a) Draw the pattern of magnetic field lines through a bar-magnet and around a current carrying solenoid.
(b) What is the pattern of magnetic field lines inside the solenoid and what does these indicate?
(c) How can a solenoid be utilised to make an electromagnet?
(d) State two ways by which the strength of this electromagnet can be increased.

(b) These are parallel straight lines indicating that magnetic field is uniform inside the solenoid.
(c) By inserting a soft iron rod into the middle part of solenoid it is used to make an electromagnet
(d) (i) By increasing the number of turns.
(ii) By increasing the strength of current.

Question. (a) State Fleming’s left hand rule.
(b) Write the principle of working of an electric motor.
(c) Explain the function of the following parts of an electric motor.
(i) Armature (ii) Brushes (iii) Split ring
Answer: (a) Fleming’s left-hand rule: Stretch the forefinger, middle finger and thumb of left hand in such a way that they are mutually perpendicular to each other. If the forefinger points in the direction of magnetic field, middle finger points in the direction of current then the thumb shows the direction of force or motion of the current carrying conductor.
(b) Principle of working of electric motor: A coil carrying electric current placed in an external magnetic field experiences a force or torque.
(c) (i) Function of armature: Enhances the power of the motor/induces motion.
(ii) Function of brushes: Helps easy transfer of charge between the coil and the external circuit.
(iii) Function of split rings: Reverses the direction of current after every half rotation of the coil, so that coil can keep rotating continuously

Question. With the help of a labelled circuit diagram describe an activity to illustrate the pattern of the magnetic field lines around a straight current carrying long conducting wire.
(i) Name the rule that is used to find the direction of magnetic field associated with a current carrying conductor.
(ii) Is there a similar magnetic field produced around a thin beam of moving:
Answer: (i) Take a battery (12 V), a variable resistor (rheostat), an Ammeter (0.5 A), a plug key, a long thick straight copper conducting wire.

(ii) Insert the thick wire through the centre normal to the plane of rectangular cardboard.
(iii) Take care that cardboard is fixed and does not slide up or down.
(iv) Connect the copper wire vertically between points X and Y as shown in diagram in series with battery, plug and a key.
(v) Sprinkle some iron flings unformly on the cardboard.
(vi) Keep the variable resistance in fixed position.
(vii) Close the key so that current flows through the wire.
(viii) Ensure the copper wires placed remains vertically straight.
(ix) Gently tap the iron filings.
Observation:
Iron filings align themselves showing a pattern of concentric circles around the copper wire which represents magnetic lines of force.
(i) Right hand rule.
(ii) (a) Yes, alpha particle being positively charged constitutes a current in the direction of motion.
(b) No, neutrons being electrically neutral constitute no current.

Question. PQ is a current carrying conductor in the plane of the paper as shown in the figure below.
(i) Find the directions of the magnetic fields produced by it at points R and S?
(ii) Given r1> r2, where will the strength of the magnetic field be larger? Give reasons.
(iii) If the polarity of the battery connected to the wire is reversed, how would the direction of the magnetic field be changed?
(iv) Explain the rule that is used to find the direction of the magnetic field for a straight current carrying conductor.

Answer: (i) The Magnetic field lines produced is into the plane of the paper at R and out of it at S.
(ii) Field at S > Field at P
Magnetic field strength for a straight current carrying conductor is inversely proportional to the distance from the wire.
(iii) The current will be going from top to bottom in the wire shown and the magnetic field lines are now in the clockwise direction on the plane which is perpendicular to the wire carrying current.
(iv) Right hand thumb rule. The thumb is aligned to the direction of the current and the direction in which the fingers are wrapped around in wire will give the direction of the magnetic field.

Question. (i) With the help of an activity, explain the method of inducing electric current in a coil with a moving magnet. State the rule used to find the direction of electric current thus generated in the coil.
(ii) Two circular coil-1 and coil-2 are kept close to each other as shown in the diagram.Coil-1 is connected to a battery and key and coil-2 with a galvanometer. State your observation
in the galvanometer:
(a) When key K closed;
(b) when key K is opened;
Answer: (i) • Take a coil of wire AB having a large number of turns.
• Connect the ends of the coil to a galvanometer as shown in figure.
• Take a strong bar magnet and move its north pole towards the end B of the coil.
• There is a momentary deflection in the needle of the galvanometer, say to the right. This indicates the presence of a current in the coil AB. The deflection becomes zero the moment the motion of the magnet stops.
• Now withdraw the north pole of the magnet away from the coil.
Now the galvanometer is deflected toward the left, showing that the current is now set up in the direction opposite to the first.
Fleming’s right hand rule is used find the direction of electric current generated in the coil.
(ii) (a) The galvanometer needle deflects momentary in one direction because when the key is closed, magnetic field lines around coil-2 increases momentarily that causes induced current in coil-2.
(b) The galvanometer needle deflects momentarily but in opposite direction because when the key is opened, magnetic field lines around coil-2 decreases momentarily that causes induced current in coil-2.

Question. What is meant by magnetic force? Name and explain the rule to determine the direction of force experienced by a current carrying conductor in a magnetic field. How does this force gets affected on:
(i) doubling the magnitude of current, (ii) reversing the direction of flow of current, (iii) reversing the direction of magnetic field.
Answer: The force experienced by a current carrying conductor when placed in a magnetic field or the force experienced by a charged particles moving in a magnetic field is called magnetic force.
Fleming left hand rule: According to this rule, on stretching the thumb, forefinger and the middle finger of your left hand such that these are perpendicular to each other, if the force finger points in the direction of magnetic field and middle finger in the direction of current, then the thumb will point in the direction of motion of force acting on the conductor.
(i) If magnitude of current is doubled, then force is doubled.
(ii) If direction of flow of current is reversed, the direction of force is also reversed.
(iii) If direction of magnetic field is reversed, the direction of force is also reversed.

Question. Explain the principle and working of an electric motor with the help of a labelled diagram. What is the function of a split ring commutator?
Answer: An electric motor converts electrical energy into mechanical energy. It works on the principle that a current carrying conductor placed in a magnetic field experiences a force.
Following are the essential parts of an electric motor.
(i) Coil: It is a rectangular coil of insulated copper wire having large number of turns.
(ii) A large permanent magnet provides strong magnetic field between its pole pieces. The coil rotates between these pole pieces.
(iii) Split rings: The two ends of coil are connected to two split rings, which are two halves of slip rings.
Working
When a current is passed through the coil, the direction of current in AB and CD is in opposite direction but both are perpendicular to magnetic field. Therefore, by Fleming’s left hand rule, arm AB of the coil experiences an upward force and arm CD experiences a downward force. These two forces being equal and opposite to each other form a couple which rotates the coil. Arms BC and DA are parallel to the field and the force between them is zero. The forces on AB and CD turns the coil in clockwise direction. After half revolution, the split rings change their position. So the direction of current in the coil reverses. The couple now acting on the coil again moves it in clockwise direction. Due to the function of split ring
commutator and brushes, coil continues to turn in clockwise direction.
Split ring commutator changes direction after every half rotation, so that the direction of current going in the coil also reverses. As a result, the coil continues to rotate in one direction. So, the electrical energy given to the coil changes into mechanical energy.

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