CBSE Class 10 Science Magnetic Effects Of Current Worksheet Set C

MCQ Questions for NCERT Class 10 Science Magnetic Effects Of Electric Current 

Question. Consider the following statements and choose the correct are:
(a) A magnet is an object which attracts pieces of iron, Nickel and cobalt
(b) Magnetic effect of electric current means that an electric current flowing in a wire produces a magnetic field around it
(c) The end of a freely suspended magnet which points towards the north direction is called the north pole of the magnet
(d) All of the above

Answer: D

Question. Two wires are placed in parallel; repulsion force and current in these two wires are “f” and “i” respectively. What will be a force if the current is doubled in each wire ?
(a) 2f
(b) f/2
(c) 2f/4
(d) 4f

Answer: D

Question. The magnetic field inside a long straight solenoid-carrying current
(a) is zero.
(b) decreases as we move towards its end.
(c) increases as we move towards its end.
(d) is the same at all points.
Answer: D

Question. Which of the following property of a proton can change while it enters freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
Answer : B

Question. The phenomenon of electromagnetic induction is:
(a) The process of charging a body
(b) The process of generating magnetic field due to a current passing through a coil
(c) Producing induced current in a coil to relative motion between a magnet and the coil
(d) The process of rotating a coil of an electric motor

Answer: C

Question. Mutual induction is a process in which current is induced in the neighbouring coil if current flows in a coil. In the figure shown below: 

(a) Maximum in situation (A)
(b) Maximum in situation (B)
(c) Maximum in situation (C)
(d) Same in all situation

Answer: A

Question. A charged particle enters at right angle into a uniform 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?
(a) Positive
(b) Negative
(c) Natural
(d) Can't decide

Answer: A

Question. For the current in a long straight solenoid N- and S-poles are created at the two ends. Among the following statements, the incorrect statement is
(a) The field lines inside the solenoid are in the form of straight lines which indicates that the magnetic field is the same at all points inside the solenoid
(b) The strong magnetic field produced inside the solenoid can be used to magnetise a piece of magnetic material like soft iron core, when placed inside the coil
(c) The pattern of magnetic field associated with the solenoid is different from the pattern of the magnetic field around a bar magnet
(d) The N- and S-poles exchange positions when the direction of current through the solenoid is reversed
Answer : C

Question. A current flows in a wire, running between the S and N poles of a magnet lying horizontally as shown in the figure below: 

The force on the wire due the magnet is directed.
(a) From N to S
(b) From S to N
(c) Vertically downwards
(d) Vertically upwards

Answer: C

Question. A student learns that magnetic field strength around a bar magnet is different at every point which diagram shows the correct magnetic field lines around a bar magnet? 

Answer: D

Question. Which of the following is not true?
(a) Induction proceeds attractions
(b) We cannot isolate a single pole
(c) We can magnetic an iron ring
(d) A permanent magnet retains its magnetism even when heated on a flame

Answer: D

Question. A finite straight wire carries a current of 3 A, where it is a 2 m long and weighs around 240 g. If it is suspended in the mid-air by a uniform magnetic field then calculate the field B. [Acceleration due to gravity = 9.8 m/s2]
(a) 0.39 T
(b) 0.42 T
(c) 0.61 T
(d) 0.37 T

Answer: A

Question. Which of the following correctly describes the magnetic field near a long straight wire?
(a) The field consists of straight lines perpendicular to the wire
(b) The field consists of straight lines parallel to the wire
(c) The field consists of radial lines originating from the wire
(d) The field consists of concentric circles centred on the wire

Answer: D

Question. The phenomenon of electromagnetic induction is
(a) the process of charging a body
(b) the process of generating magnetic field due to a current passing through a coil
(c) producing induced current in a coil due to relative motion between a magnet and the coil
(d) the process of rotating a coil of an electric motor

Answer: C

Question. The device used for producing electric current is called a
(a) generator
(b) galvanometer
(c) ammeter
(d) motor

Answer: A

Question. The essential difference between an AC generator and a DC generator is that
(a) AC generator has an electromagnet while a DC generator has permanent magnet.
(b) DC generator will generate a higher voltage.
(c) AC generator will generate a higher voltage.
(d) AC generator has slip rings while the DC generator has a commutator.

Answer: D

Question. At the time of short circuit, the current in the circuit
(a) reduces substantially
(b) does not change
(c) increases heavily
(d) vary continuously

Answer: C

Question. The process of inducing a current in a coil of wire by placing it ina region of changing magnetic field is:
(a) Electrical effect
(b) Heating effect of current
(c) Magnetic effect of current
(d) Electromagnetic induction

Answer: D

Question : Why does a compass needle get deflected when brought near a bar magnet?
Answer : The needle of a compass is a small magnet. That’s why when a compass needle is brought near a bar magnet, its magnetic field lines interact with that of the bar magnet. Hence, a compass needle gets deflected. 

Question : What type of core is used to make electromagnets?
                                  OR
What type of core should be put inside a current-carrying solenoid to make an electromagnet?
Answer : Soft Iron

Question : How is magnetic field produced in a solenoid used?
Answer : It is used to magnetise a soft iron bar to form an electromagnet.

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 : Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from the back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of the magnetic field?
Answer : The direction is vertically downwards

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 : Suggest one way to distinguish a wire carrying current from a wire carrying no current.
Answer : The magnetic compass needle will get deflected near the wire current carrying but not near the wire with no current

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 : 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 : 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 : What does the direction of thumb indicate in the right hand thumb rule?
Answer : The thumb indicates the direction of current in the straight conductor held by curved fingers of our hand.

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 : Why are magnetic field lines form closed curves?
Answer : It is because outside the magnet, magnetic field lines start from north pole and merge at south pole whereas inside the magnet they start from south pole and merge at north pole, therefore these lines from closed curves.

Short Answer type Questions :

Question : Draw magnetic field lines around a bar magnet.
Answer :  Magnetic field lines of a bar magnet emerge from the north pole and terminate at the south pole. Inside the magnet, the field lines emerge from the south pole and terminate at the north pole, as shown in the given figure.

Question : List the properties of magnetic lines of force.
Answer :  The properties of magnetic lines of force are as follows.
→ Magnetic field lines emerge from the north pole.
→ They merge at the south pole.
→ The direction of field lines inside the magnet is from the south pole to the north pole.
→ Magnetic lines do not intersect with each other.

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 : Inside the loop = Pierce inside the table Outside the loop = Appear to emerge out from the table For downward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop. Similarly, for upward direction of current flowing in the circular loop, the direction of magnetic field lines will be as if they are emerging from the table outside the loop and merging in the table inside the loop, as shown in the given figure.

Question : The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer : 

The magnetic field lines inside a current-carrying long straight solenoid are uniform.

Question : In Activity 13.7 (page: 230), how do we think the displacement of rod AB will be affected if (i) current in rod AB is increased: (ii) a stronger horse-shoe magnet is used: and (iii) length of the rod AB is increased?
Answer : (i) If the current in the rod is increased then rod will be deflected with greater force.
(ii) If a stronger horse-shoe magnet is used then also rod will be deflected with greater force due to the increase in magnetic field.
(iii) If the length of the rod AB is increased.

Question : State Fleming's left-hand rule.
Answer : Fleming's left hand rule states that if we arrange the thumb, the centre finger, and the forefinger of the left hand at right angles to each other, then the thumb points towards the direction of the magnetic force, the centre finger gives the direction of current, and the forefinger points in the direction of magnetic field.

Question : What is the principle of an electric motor?
Answer : The principle of an electric motor is based on the magnetic effect of electric current. A current-carrying loop experiences a force and rotates when placed in a magnetic field.
The direction of rotation of the loop is according to the Fleming’s left-hand rule.

Question : What is the role of the split ring in an electric motor?
Answer : The split ring in the electric motor also known as a commutator reverses the direction of current flowing through the coil after every half rotation of the coil. Due to this the coil continues to rotate in the same direction.

Question : Explain different ways to induce current in a coil.
Answer : The different ways to induce current in a coil are as follows:
→ If a coil is moved rapidly between the two poles of a horse-shoe magnet, then an electric current is induced in the coil.
→ If a magnet is moved relative to a coil, then an electric current is induced in the coil.

Question : State the principle of an electric generator.
Answer : Electric generator works on the principle of electromagnetic induction. Electricity is generated by rotating a coil inside magnetic field.

Question : Name some sources of direct current.
Answer : Some sources of direct current are cell, DC generator, etc.

Question : Which sources produce alternating current?
Answer : AC generators, power plants, etc., produce alternating current.

Question : Name two safety measures commonly used in electric circuits and appliances.
Answer : Two safety measures commonly used in electric circuits and appliances are
→ Electric Fuse: An electric fuse is connected in series it protects the circuit from overloading and prevents it from short circuiting.
→ Proper earthing of all electric circuit in which any leakage of current in an electric appliance is transferred to the ground and people using the appliance do not get the shock.

Question : An electric oven of 2 kW is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer : Current drawn by the electric oven can be obtained by the expression,
P = VI
Where,
Current = I
Power of the oven, P = 2 kW = 2000 W
Voltage supplied, V = 220 V
I = 2000/220 V = 9.09 A
Hence, the current drawn by the electric oven is 9.09 A, which exceeds the safe limit of the circuit. Fuse element of the electric fuse will melt and break the circuit.

Question : What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer : The precautions that should be taken to avoid the overloading of domestic circuits are as follows:
→ Too many appliances should not be connected to a single socket.
→ Too many appliances should not be used at the same time.
→ Faulty appliances should not be connected in the circuit.
→ Fuse should be connected in the circuit.

Question : List three sources of magnetic fields.
Answer : Three sources of magnetic fields are as follows:
→ Current-carrying conductors
→ Permanent magnets
→ 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 bar magnet? Explain.
Answer : A solenoid is a long coil of circular loops of insulated copper wire. Magnetic field lines are produced around the solenoid when a current is allowed to flow through it. The magnetic field produced by it is similar to the magnetic field of a bar magnet. The field lines produced in a current-carrying solenoid is shown in the following figure

In the above figure, when the north pole of a bar magnet is brought near the end connected to the negative terminal of the battery, the solenoid repels the bar magnet. Since like poles repel each other, the end connected to the negative terminal of the battery behaves as the north pole of the solenoid and the other end behaves as a south pole. Hence, one end of the solenoid behaves as a north pole and the other end behaves as a south pole.

Question : When is the force experienced by a current-carrying conductor placed in a magnetic field largest?
Answer : The force experienced by a current-currying conductor is the maximum when the direction of current is perpendicular to the direction of the magnetic field.

Question : Imagine that you are sitting in a chamber with your back to one wall. An electron beam, moving horizontally from back wall towards the front wall, is deflected by a strong magnetic field to your right side. What is the direction of magnetic field?
Answer : The direction of the magnetic field is vertically downwards. The direction of current is from the front wall to the back wall because negatively charged electrons are moving from back wall to the front wall. The direction of magnetic force is rightward. Hence, using Fleming's left hand rule, it can be concluded that the direction of magnetic field inside the chamber is downward.

Question : Draw a labelled diagram of an electric motor. Explain its principle and working. What is the function of a split ring in an electric motor? 

Answer : Principle: It works on the principle of the magnetic effect of current. A current-carrying
coil rotates in a magnetic field. Working: When a current is allowed to flow through the coil MNST by closing the switch, the coil starts rotating anti-clockwise. This happens because a downward force acts on length MN and at the same time, an upward force acts on length ST. As a result, the coil rotates anti-clockwise.
Current in the length MN flows from M to N and the magnetic field acts from left to right, normal to length MN. Therefore, according to Fleming's left hand rule, a downward force acts on the length MN. Similarly, current in the length ST flows from S to T and the magnetic field acts from left to right, normal to the flow of current. Therefore, an upward force acts on the length ST. These two forces cause the coil to rotate anti-clockwise. After half a rotation, the position of MN and ST interchange. The half-ring D comes in contact with brush A and half-ring C comes in contact with brush B. Hence, the direction of current in the coil MNST gets reversed.
The current flows through the coil in the direction TSNM. The reversal of current through the coil MNST repeats after each half rotation. As a result, the coil rotates unidirectional.
The split rings help to reverse the direction of current in the circuit. These are called the commutator.

Question : Name some devices in which electric motors are used?
Answer : Some devices in which electric motors are Water pumps, Electric fans, Electric mixers and Washing machines.

Question : A coil of insulated copper wire is connected to a galvanometer. What will happen if a bar magnet is (i) pushed into the coil, (ii) withdrawn from inside the coil, (iii) held stationary inside the coil?
Answer : (i) The needle of the galvanometer shows a momentary deflection in a particular direction.
(ii) The needle of the galvanometer shows a momentarily in the opposite direction.
(iii) The needle of the galvanometer shows no deflection.

Question : Two circular coils A and B are placed closed to each other. If the current in the coil A is changed, will some current be induced in the coil B? Give reason.
Answer : Two circular coils A and B are placed close to each other. When the current in coil A is
changed, the magnetic field associated with it also changes. As a result, the magnetic
field around coil B also changes. This change in magnetic field lines around coil B
induces an electric current in it. This is called electromagnetic induction.

Question : State the rule to determine the direction of a (i) magnetic field produced around a straight conductor-carrying current, (ii) force experienced by a current-carrying straight conductor placed in a magnetic field which is perpendicular to it, and (iii) current induced in a coil due to its rotation in a magnetic field.
Answer : (i) Maxwell's right hand thumb rule
(ii) Fleming's left hand rule
(iii) Fleming's right hand rule

Question : Explain the underlying principle and working of an electric generator by drawing a labelled diagram. What is the function of brushes?
Answer : Principle: An electric generator works on the principle of electromagnetic induction phenomenon. According to it, whenever a coil is rotated between the poles of a magnet, an induced current is set up in the coil, whose direction is given by Fleming’s right hand rule.

Working: Let in the beginning, as shown in Fig. brushes B₁ and B₂ are kept pressed
separately on rings R₁ and R₂ respectively. Let the axle attached to the rings is rotated
such that arm AB of the coil moves up and arm CD moves down in the magnetic field.
Due to rotation of arms AB and CD induced currents are set up in them. As per Fleming’s right hand rule induced currents in these arms are along the directions AB and CD. Thus an induced current flows along ABCD and current in the external circuit flows from B₂ to B₁.
After half a rotation, arm AB starts moving down and the arm CD upward. Therefore, directions of induced currents in these arms change. Thus net induced current now becomes in the direction DCBA. In the external circuit now current flows from B₂ to B₁
Thus after every half rotation current changes its direction and an alternating current is obtained from the generator.
Function of Brushes: Brushes are kept pressed on the two slip tings separately. Outer ends of the brushes are connected to the galvanometer (or the external load). Thus brushes help in transferring current from the coil ABCD to the external circuit.

Question : When does an electric short circuit occur?
Answer : If the insulation of the wires used in the circuit is damaged or the appliance used is faulty due to which the live wire and the neutral wire comes in direct contact as a result current in the circuit rises and the short circuit occurs.

Question : What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer : The metallic body of electric appliances is connected to the earth by means of earth wire so that any leakage of electric current is transferred to the ground. This prevents any electric shock to the user. That is why earthing of the electrical appliances is necessary.