NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

These NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current Questions and Answers are prepared by our highly skilled subject experts to help students while preparing for their exams.

Magnetic Effects of Electric Current NCERT Solutions for Class 10 Science Chapter 13

Class 10 Science Chapter 13 Magnetic Effects of Electric Current InText Questions and Answers

In-text Questions (Page 224)

Question 1.
Why does a compass needle get deflected when brought near a bar magnet ?
Answer:
A compass needle is a small bar magnet, so it is deflected when brought near a bar magnet.

In-text Questions (Page 228)

Question 1.
Draw magnetic field lines around a bar magnet.
Answer:
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 1

Question 2.
List the properties of magnetic field lines.
Answer:

  • The magnetic line of force emerge from north pole and merge at the south pole.
  • Inside the magnet, the direction of field lines is from its south pole to its north pole.
  • The closeness of the lines shows the degree relative strength of the magnetic field.
  • No two field lines are closed to each other.

Question 3.
Why don’t two magnetic field lines intersect each other ?
Answer:
If two magntic lines are found to cross each other, it would mean that at the point cf inter-section, the compass needle would point towards two directions, which is not possible.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

In-text Questions (Page 229)

Question 1.
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 the magnetic field will be downward and perpendicular to the table inside the loop. And outside the loop magnetic field lies in the upward direction.

Question 2.
The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
Uniform magnetic field in a region is represented by parallel straight line as follows :
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 2

Question 3.
Choose the correct option.
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) is the same at all points.

In-text Questions (Page 231)

Question 1.
Which of the following property of a proton can change while it moves freely in a magnetic field? (There may be more than one correct answer.)
(a) mass
(b) speed
(c) velocity
(d) momentum
Answer:
(c) Velocity
(d) Momentum

Question 2.
In Activity 13.7, 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) Displacement of the rod towards left increases.
(ii) Displacement of the rod again increases.
(iii) Displacement increases.

Because as current, length and magnetic field increase, the force of attraction or repulsion between the wire and magnet increases.

Question 3.
A positively-charged particle (alpha- particle) projected towards west is deflected towards north by a magnetic field. The direction of magnetic field is
(a) towards south
(b) towards east
(c) downward
(d) upward
Answer:
(c) Downward.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

In-text Questions (Page 233)

Question 1.
State Fleming’s left-hand rule.
Answer:
According to this, stretch the thumb, forefinger and middle finger of you left hand such that they are mutually perpendicular. If the first finger points in the direction of magnetic field and the second finger in the direction of current then the thumb will point in the direction of motion or the force acting on the conductor.

Question 2.
What is the principle of an electric motor?
Answer:
It is based on the principle that when a rectangular coil is placed in a magnetic field and a current is passed through it, a torque acts on the coil which rotates it continuously.

Question 3.
What is the role of the split ring in an electric motor?
Answer:
In electric motor, the split ring acts as a commutator.

In-text Questions (Page 236)

Question 1.
Explain different ways to induce current in a coil.
Answer:
The ways to induce current in as coil are:

  1. By changing the magnetic field : Current can be induced in a coil by changing the magnitude of the magnetic field.
  2. By moving a coil in the magnetic field : Current can be induced in a coil by moving coil in the magnetic field.

In-text Questions (Page 237)

Question 1.
State the principle of an electric generator.
Answer:
It is based on the phenomenon of electromagnetic induction i.e., when a coil is moved in a magnetic field, a induced current is produced in the coil.

Question 2.
Name some sources of direct current.
Answer:
D.C. generator, Dry Cell, Battery.

Question 3.
Which sources produce alternating current?
Answer:
A.C. generator, Dynamo.

Question 4.
Choose the correct option.
A rectangular coil of copper wires is rotated in a magnetic field. The direction of the induced current changes once in each
(a) two revolutions
(b) one revolution
(c) half revolution
(d) one-fourth revolution
Answer:
(c) Half revolution

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

In-text Questions (Page 238)

Question 1.
Name two safety measures commonly used in electric circuits and appliances.
Answer:
Earth wire, Electric fuse.

Question 2.
An electric oven of 2 kW power rating is operated in a domestic electric circuit (220 V) that has a current rating of 5 A. What result do you expect? Explain.
Answer:
The resistance of electric oven, say R
∴ P = I2 × R
2 × 100 W = (5 A)2 × R
R = \(\frac{2 \times 100 \mathrm{~W}}{25 \mathrm{~A}^{2}}\) = 80 ohm
Now, this electric oven is connected with 220 V so the current drawn by the appliances.
V = 1
⇒ 1 = \(\frac{V}{R}=\frac{220 \mathrm{~V}}{80 \mathrm{ohm}}\) = 2.73 A

Question 3.
What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer:
A fuse in a circuit is used to avoid overloading. Overloading can occur when the live wire and neutral wire come into direct contact. In such a situation, the current in the circuit abruptly increases. The use of an electric fuse prevents the electric circuit and the appliance from a possible damage by stopping the flow of unduly high electric current.

Class 10 Science Chapter 13 Magnetic Effects of Electric Current Textbook Questions and Answers

Page no. 240

Question 1.
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 centered on the wire.
Answer:
(d) The field consists of concentric circles centered on the wire.

Question 2.
The phenomenon of electromagnetic induction is wire.
(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 a relative motion between a magnet and the coil.
(d) the process of rotating a coil of an electric motor.
Answer:
(c) Producing induced current in a coil due to relative motion between 1 magnet and the coil.

Question 3.
The device used for producing electric current is called a
(a) galvanometer
(b) generator
(c) motor
(d) ammeter
Answer:
(a) Generator.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Question 4.
The essential difference between 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) AC generator has slip rings while the DC generator has a commutator.

Question 5.
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) Increase heavily

Question 6.
State whether the following statements are true or false:
(a) An electric motor converts mechanical energy into electric energy
(b) An electric generator works on the principle of electromagnetic induction.
(c) The field at the Centre of a long circular coil carrying current will be parallel straight lines.
(d) A wire with a green insulation is usually the live wire.
Answer:
(a) False,
(b) True,
(c) True,
(d) False.

Question 7.
List three sources of magnetic fields.
Answer:
Solenoid, Bar magnet, Magnetite.

Question 8.
How does a solenoid behave like a magnet ? Can you determine the north and south poles of a current carrying solenoid with a help of bar magnet ? Explain.
Answer:
A solenoid is a long, helically round coil of insulated Wire.

When an electric current flows through a solenoid a magnetic field is set up which is similar to the magnetic field of a bar magnet. One end of the solenoid acts as south pole and the other end acts as north pole. If the current flows in a clockwise direction when the coil is seen end-on, then that end of the solenoid acts as a South pole. On the other hand if the current flows in anticlockwise direction when the coil is seen-end- on, then that end of the solenoid acts as a North pole.

When the North pole of a bar magnet is placed near the one end of the solenoid and if it is repelled, then end of the solenoid will be North pole and if it is attracted than end of the solenoid will be South pole.

Question 9.
When is the force experienced by a current-carrying conductor placed in a magnetic field is largest ?
Answer:
The force will be largest when the direction of current is at right angles to the direction of the magnetic field.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Question 10.
Imagine 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. Hat is the direction of magnetic field?
Answer:
Magnetic field is horizontally towards front wall.

Question 11.
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: Electric motor is based on the principle that “when a current carrying conductor is placed in a magnetic field Then it experiences a mechanical force tending to rotate the Conductor” and the direction of the force experienced is given by Fleming’s Left Hand Rule.

Working : Suppose D.C. current (from a battery) is passed via Brushes, and commutator through armature, when the plane of The coil ABCD is parallel to the magnetic field as shown in Fig. (a) According to Fleming’s left hand rule, the limb AB of the coil Experiences an upward force. While the limb CD experiences a Downward force: Now these two equal, but opposite forces acting At AB and CD constitutes a couple, which rotates the coil in Clockwise direction. It may be noted that the moment of the couple
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 3
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 4
is maximum to start with, but it goes on decreasing and becomes Zero, when the coil becomes perpendicular to magnetic lines of Force. Consequently, the coil should stop at this position. However Due to inertia of the moving coil, it crosses this position and the Coil again becomes parallel to the magnetic lines of force Contact of the brushes (B1 and B2) with the segments (S1 and S2) Gets reversed and the direction of current through the coil also gets Reversed, thereby the current starts flowing along DCBA as shown In Fig. (b): Consequently, the limb DC of the coil starts moving Upwards; while the limb AB os the coil starts moving downwards In accordance with Fleming’s left hand rule. In this way, the Motion of the armature is always same (clockwise, in this case) And becomes continuous.

Question 12.
Name some devices in which electric motors are used.
Answer:
Fans, Cooler, Air conditioner, CD Player etc.

Question 13.
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) with drawn from inside the coil (iii) held stationary Inside the coil ?
Answer:
(i) We will see a deflection in the galvanometer.
(ii) The needle of galvanometer again shows deflection, but in The opposite direction.
(iii) No deflection in the galvanometer.

Question 14.
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:
Yes, some current will be induced in the coil B as Current is changed in coil A due to electromagnetic induction. In electromagnetic induction by changing magnetic field in a conductor induces a current in another conductor because as the Current changes in coil ‘A the magnetic field associated with it. Also changes. Thus the magnetic field lines around the coil B Also change. Hence the chance magnetic field lines associated With the coil ‘B’ is the cause of the induced current in it.

Question 15.
State the rule to determine the direction of a (i) Magnetic field produced around a straight conductor Current (ii) force experienced by a Current-carrying straight Conductor placed in a magnetic field which is perpendicular it and (iii) current induced in a coil due to its rotation Magnetic field.
Answer:
(i) Right hand thumb rule
(ii) Flemings left hand rule
(iii) Fleming’s right hand rule.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Question 16.
Explain the underlying principle and working of an Electric generator by drawing a labelled diagram. What is The Function of brushes?
Answer:
Principle : It is based on the principle Electromagnetic induction, Which states in simple form As “whenever a conductor is Rotated mechanically in a Magnetic field, there is a Brushes Change in the magnetic lines of force within it and an Induced current is generated In the conductor”. The Direction of induced current is given by Fleming’s right hand rule.

Construction : It consists of a rotating armature ABCD containing coils of wire, pole pieces, brushes and a commutator. The two ends of the armature ABCD are connected to two metallic Rings S1 and S2 the two brushes B1 and B2 which are connected To a galvanometer G are in contact with the rings S1 and S2 Respectively.

Working : When the armature coil ABCD rotates in the magnetic field provided by the strong field magnet, it cuts the magnetic lines of force. Thus the changing magnetic field produces induced current in the coil. The current flows out through the brush B, in one direction in the first half of the revolution and through the Brush B, in the next half revolution in the reverse direction. This Process is repeated. Therefore, induced current produced is of alternating nature. Such a current is called alternating current.
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 5

Question 17.
When does an electric short circuit occur?
Answer:
If the plastic insulation of the live wire and neutral wire gets torn, than the two wires touch each other. The touching of the live wire and neutral wire directly is known as short circuiting. It occurs by the direct touching of live and neutral wires.

Question 18.
What is the function of an earth wire ? Why is it necessary to earth metallic appliances?
Answer:
Function : A very high current flows through the earth Wire and the fuse of household wiring blows out or melts and it cuts of the power supply. We earth the metallic appliances to save ourselves from electric shocks. If by chance, the live wire touches. The metal part of the electric appliance, which has been earthed, then the current passes directly to the earth through the earth wire. It does not need our body to pass the current and thus we do not get an electric shock.

Class 10 Science Chapter 13 Magnetic Effects of Electric Current Textbook Activities

Activity 13.1 (Page 223)

  • Take a straight thick copper wire and place it between the points X and Y in an electric circuit, as shown in Fig.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 6
Fig. : Compass needle is deflected on passing an electric current through a metallic conductor

  • place a small compass near to this copper wire. See the position of its needle.
  • Pass the current through the circuit by inserting the key into the plug.

Question 1.
Observe the change in the position of the compass needle.
Answer:
We see that the needle is deflected.

Question 2.
What does it mean ?
Answer:
It means that the electric current through the copper wire has produced a magnetic effect. Thus we can say that electricity and magnetism are linked to each other.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Activity 13.2 (Page 223)

  • Fix a sheet of white paper on a drawing board using some adhesive material.
  • Place a bar magnet in the centre of it,
  • Sprinkle some iron filings uniformly around the bar magnet (Fig. ). A salt- sprinklei may be used for this purpose.
  • Now tap the board gently.

Question 1.
What do you observe?
Answer:
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 7
The iron filings arrange themselves in a pattern as shown Fig. Why do the iron filings arrange in such a pattern? What does this pattern demonstrate? The magnet exerts its influence in the region surrounding it. Therefore the iron filings experience a force. The force thus exerted makes iron filings to arrange in a pattern. The region surrounding a magnet, in which the force of the magnet can be detected, is said to have a magnetic field. The lines along which the iron filings align themselves represent magnetic field lines.

Activity 13.3 (Page 224)

  • Take a small compass and a bar magnet.
  • Place the magnet on a sheet of white paper fixed on a drawing board, using some adhesive material.
  • Mark the boundary of the magnet.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 8
Fig. : (a) Drawing a magnetic field line with the help of a compass needle

  • Place the compass near the north pole of the magnet. How does it behave? The south pole of the needle points towards the north pole of the magnet. The north pole of the compass is directed away from the north pole of the magnet.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 9

  • Mark the position of two ends of the needle.
  • Now move the needle to a new position such that its south pole occupies the position previously occupied by its north pole.
  • In this way, proceed step by step till you reach the south pole of the magnet as shown in Fig. (a).
  • Join the points marked on the paper by a smooth curve. This curve represents a field line.
  • Repeat the above procedure and draw as many lines as you can. You will get a pattern shown in Fig. (b). These lines represent the magnetic field around the magnet. These are known as magnetic field lines.
  • Observe the deflection in the compass needle as you move; it along a field line. The deflection increases as the needle is moved towards the poles.

Observations : Magnetic field is a quantity that has both direction and magnitude. The direction of the magnetic field is taken to be the direction in which a north pole of the compass needle moves inside it. Therefore it is taken by convention that the field lines emerge from north pole and merge at the south pole (note the arrows marked on the field lines in Fig. (b). Inside the magnet, the direction of field lines is from its south pole to its north pole. Thus the magnetic field lines are closed curves.

The relative strength of the magnetic field is shown by the degree of closeness of the field lines. The field is stronger, that is, the force acting on the pole of another magnet placed is greater where the field lines are crowded (see Fig. (b).

No two field-lines are found to cross each other. If they did, it would mean that at the point of intersection, the compass needle would point towards two directions, which is not possible.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Activity 13.4 (Page 226)

  • Take a long straight copper wire, two or three cells of 1.5 V each, and a plug key. Connect all of them in series as shown in Fig. (a).
  • Place the straight wire parallel to and over a compass needle.
  • Plug the key in the circuit.
  • Observe the direction of deflection of the north pole of the needle. If the current flows from north to south, as shown in Fig. (a), the north pole of the compass needle would move towards the east.
  • Replace the cell connections in the circuit as shown in Fig. (b). This would result in the change of the direction of current through the copper wire, that is, from south to north.
  • Observe the change in the direction of deflection of the needle. You will see that now the needle moves in opposite direction, that is, towards the west [Fig.] It means that the direction of magnetic field produced by the electric current is also reversed.

Observations:
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 10
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 11
Fig.: A simple electric circuit in which a straight copper wire is placed parallel to and over a compass needle. The deflection in the needle becomes opposite when the direction of the current is reversed.

Activity 13.5 (Page 226)

  • Take a battery (12 V), a variable resistance (or a rheostat), an ammeter (0-5 A), a plug key, connecting wires and a long straight thick copper wire.
  • Insert the thick wire through the centre, normal to the plane of a rectangular cardboard. Take care that the cardboard is fixed and does not slide up or down.
  • Connect the copper wire vertically between the points X and Y, as shown in Fig. (a), in series with the battery, a plug and key.
  • Sprinkle some iron filings uniformly on the cardboard. (You may use a salt sprinkler for this purpose.)
  • Keep the variable of the rheostat at a fixed position and note the current through the ammeter.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 12

  • Close the key so that a current flows through the wire. Ensure that the copper wire placed between the points X and Y remains vertically straight.
  • Gently tap the cardboard a few times. Observe the pattern of the iron filings. You would find that the iron filings align themselves showing a pattern of concentric circles around the copper wire (Fig. a).
  • What do these concentric circles represent? They represent the magnetic field lines.
  • Flow can the direction of the magnetic field be found? Place a compass at a point (say P) over a circle. Observe the direction of the needle. The direction of the north pole of the compass needle would give the direction of the field lines produced by the electric current through the straight wire at point P. Show the direction by an arrow.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 13
Fig. : (a) A pattern of concentric circles indicating the field lines of a magnetic field around a straight conducting wire. The arrows In the circles show the direction of the field lines (b) A close up of the pattern obtained

Does the direction of magnetic field lines get reversed if the direction of current through the straight copper wire is reversed? Check it.

Observations: What happens to the deflection of the compass needle placed at a given point if the current in the copper wire is changed? To see this, vary the current in the wire. We find that the deflection in the needle also changes. In fact, if the current is increased, the deflection also increases. It indicates that the magnitude of the magnetic field produced at a given point increases as the current through the wire increases.

What happens to the deflection of the needle if the compass is moved away from the copper wire but the current through the wire remains the same? To see this, now place the compass at a farther point from the conducting wire (say at point Q). What change do you observe? We see that the deflection in the needle decreases. Thus the magnetic field produced by a given current in the conductor decreases as the distance from it increases. From Fig. it can be noticed that the concentric circles representing the magnetic field around a current-carrying straight wire become larger and larger as we move away from it.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Activity 13.6 (Page 229)

  • Take a rectangular cardboard having two holes. Insert a circular coil having large number of turns through them, normal to the plane of the cardboard.
  • Connect the ends of the coil in series with a battery, a key and a rheostat, as shown in Fig. (a).
  • Sprinkle iron filings uniformly on the cardboard.
  • Plug the key.
  • Tap the cardboard gently a few times. Note the pattern of the iron filings that emerges on the cardboard.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 14
Fig. : (a) Magnetic field produced by a current-carrying circular coil

Observations : A coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. The pattern of the magnetic field lines around a current-carrying solenoid is shown in Fig. (h). Compare the pattern of the field with the magnetic field around a bar magnet (Fig.). Do they look similar? Yes, they are similar. In fact, one end of the solenoid behaves as a magnetic north pole, while the other behaves as the south pole. The field lines inside the solenoid are in the form of parallel straight lines This indicates that the magnetic field is the same at all points inside the solenoid. That is, the field is uniform inside the solenoid.
NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 15
Fig. : (b) Field lines of the magnetic field through and around a current carrying solenoid.

Activity 13.7 (Page 230)

  • Take a small aluminium rod AB (of about 5 cm). Using two connecting wires suspend it horizontally from a stand, as shown in Fig.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 16
Fig. : A current carrying rod, AB, experiences a force perpendicular to its length and the magnetic field

  • Place a strong horse-shoe magnet in such a way that the rod lies between the two poles with the magnetic field directed upwards. For this put the north pole of the magnet vertically below and south pole vertically above the aluminium rod (Fig.).
  • Connect the aluminium rod in series with a battery, a key and a rheostat.
  • Now pass a current through the aluminium rod from end B to end A.
  • What do you observe? It is observed that the rod is displaced towards the left. You will notice that the rod gets displaced.
  • Reverse the direction of current flowing through the rod and observe the direction of its displacement. It is now towards the right.
  • Why does the rod get displaced?

Observation: The displacement of the rod in the above activity suggests that a force is exerted on the current-carrying aluminium rod when it is placed in a magnetic field. It also suggests that the direction of force is also reversed when the direction of current through the conductor is reversed. Now change the direction of field to vertically downwards by interchanging the two poles of the magnet. It is once again observed that the direction of force acting on the current-carrying rod gets reversed. It shows that the direction of the force on the conductor depends upon the direction of current and the direction of the magnetic field. Experiments have shown that the displacement of the rod is largest (or the magnitude of the force is the highest) when the direction of current is at right angles to the direction of the magnetic field. In such a condition we can use a simple rule to find the direction of the force on the conductor.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Activity 13.8 (Page 233)

  • Take a coil of wire AB having a large number of turns.
  • Connect the ends of the coil to a galvanometer as shown in Fig.
  • Take a strong bar magnet and move its north pole towards the end B of the coil. Do you find any change in the galvanometer needle?

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 17
Fig. : Moving a magnet towards a coll sets up a current in the coll circuit, as Indicated by deflection in the galvanometer needle

  • 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.
  • Place the magnet stationary at a point near to the coil, keeping its north pole towards the end B of the coil. We see that the galvanometer needle deflects toward the right when the coil is moved towards the north pole of the magnet. Similarly the needle moves toward left when the coil is moved away.
  • When the coil is kept stationary with respect to the magnet, the deflection of the galvanometer drops to zero. What do you conclude from this activity?

Observations : A galvanometer is an instrument that can detect the presence of a current in a circuit. The pointer remains at zero (the centre of the scale) for zero current flowing through it. It can deflect either to the left or to the right of the zero mark depending on the direction of current.

We can also check that if you had moved south pole of the magnet towards the end B of the coil, the deflections in the galvanometer would just be opposite to the previous case. When the coil and the magnet are both stationary, there is no deflection in the galvanometer. It is, thus, clear from this activity that motion of a magnet with respect to the coil produces an induced potential difference, which sets up an induced electric current in the circuit.

Activity 13.9 (Page 235)

  • Take two different coils of copper wire having large number of turns (say 50 and 100 turns respectively). Insert them over a non-conducting cylindrical roll, as shown in Fig (You may use a thick paper roll for this purpose.)
  • Connect the coil-1, having larger number of turns, in series with a battery and a plug key. Also connect the other coil-2 with a galvanometer as shown.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current 18

  • Plug in the key. Observe the galvanometer. Is there a deflection in its needle? You will observe that the needle of the galvanometer instantly jumps to one side and just as quickly returns to zero, indicating a momentary current in coil- 2.
  • Disconnect coil-1 from the battery. You will observe that the needle momentarily moves, but to the opposite side. It means that now the current flows in the opposite direction in coil-2.

Observations: In this activity we observe that as soon as the current in coil-1 reaches either a steady value or zero, the galvanometer in coil-2 shows no deflection.

From these observations, we conclude that a potential difference is induced in the coil-2 whenever the electric current through the coil-1 is changing (starting or stopping). Coil-1 is called the primary coil and coil-2 is called the secondary coil. As the current in the first coil changes, the magnetic field associated with it also changes. Thus the magnetic field lines around the secondary coil also change. Hence the change in magnetic field lines associated with the secondary coil is the cause of induced electric current in it. This process, by which a changing magnetic field in a conductor induces a current in another conductor, is called electromagnetic induction. In practice we can induce current in a coil either by moving it in a magnetic field or by changing the magnetic field around it. It is convenient in most situations to move the coil in a magnetic field.

Class 10 Science Chapter 13 Magnetic Effects of Electric Current Additional Important Questions and Answers

Very Short Answer Type Questions

Question 1.
In household circuits is a fuse wire connected in Series or in parallel.
Answer:
Series.

Question 2.
What is an electric generator ?
Answer:
A device which converts mechanical energy into electrical energy.

Question 3.
What are the various components of an electric motor?
Answer:

  • Magnet
  • brushes
  • coil
  • commutator.

Question 4.
What is meant by back e.m.f. in a motor ?
Answer:
Back e.m.f. means induced e.m.f. in a motor.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Question 5.
What is electric motor ?
Answer:
A device which converts electric energy into mechanical energy.

Short Answer Type Questions

Question 1.
What is the source of magnetic field ?
Answer:
The origin of magnetic field is electrical. The electrons That revolve in an atom act as tiny current loops are responsible for generating the magnetic field.

Question 2.
What is the basic difference between electric lines of force and magnetic lines of force.
Answer:
The electric lines of force originate from positive charge End as negative charge hence there is discontinuous curve. On the other hand, magnetic lines of force are dosed loops because Isolated magnetic poles do not exist.

Question 3.
Give some ways to increase the magnitude of induced current.
Answer:
The ways to increase the magnitude of induced current are as follows:

  • Magnitude of induced current can be increased by Increasing the strength of used magnetic field.
  • It can be increased if the speed of movement of the conduction in the magnetic field is increased.
  • It can also be increased if the conductor is taken in the form of rectangular coil of many turns of insulated wire.

Long Answer Type Question

Question 1.
Why electric voltage is stepped up for transmission?
Answer:
Mathematically, Power = voltage × current.

When the electric voltage is stepped up, the potential differences increases and current decreases so that the power remains the same When there is transmission of electricity over large distances. Through the wires, the wires get heated and the heat thus produced is in the atmosphere. Heat produced is I2R where 1 is the current flowing through the wire. When the voltage is stepped up, the current I that flows through the wire gets decreased and hence I2R become small and there would be small heat loss or power less. During transmission. Hence to minimize the power loss during transmission, the electric voltage is stepped up.

NCERT Solutions for Class 10 Science Chapter 13 Magnetic Effects of Electric Current

Multiple Choice Questions

Question 1.
Magnetic field produced at the Centre of a current-carrying Circular wire is
(a) directly proportional to the square of the radius of the circular wire.
(b) directly proportional to the radius of the circular wire
(c) Inversely proportional to the square of the radius of the inversely Circular wire
(d) Inversely proportional to the radius of the circular wire
Answer:
(d) Inversely proportional to the radius of the circular wire

Question 2.
Fuse in an electric circuit acts as a
(a) Current multiplier
(b) Voltage multiplier
(c) Power multiplier
(d) Safety device
Answer:
(d) Safety device

Question 3.
Who invented generator ?
(a) Oersted
(b) Coulomb
(c) Rutherford
(d) Faraday
Answer:
(d) Faraday

Question 4.
The frequency of household supply of a.c. is
(a) 45 Hz
(b) 50 Hz
(c) 60 Hz
(d) 100 Hz
Answer:
(b) 50 Hz

Question 5.
The value of magnetic dip at magnetic
(a) 0°
(b) 30°
(c) 90°
(d) 180°
Answer:
(c) 90°

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