RBSE Class 10 Science Solutions Chapter 13 Magnetic Effects of Electric Current
RBSE Class 10 Science Solutions Chapter 13 Magnetic Effects of Electric Current
RBSE Class 10 Science Chapter 13 Magnetic Effects of Electric Current InText Questions and Answers
Page 224.
Question 1.
Why does a compass needle get deflected when brought near a bar magnet?
Answer:
The compass needle is made of very small magnet which has both north and south pole. When compass needle is bring near a bar magnet, the same poles of compass needle and bar magnet repel and opposite poles attract to each other hence needle gets deflected.
Page 228.
Question 1.
Draw magnetic field lines around a bar magnet.
Answer:
Question 2.
List the properties of magnetic field lines.
Answer:
Properties of Magnetic Field Lines:
- Magnetic field lines arises from the north pole and end at the south pole of the bar magnet.
- Magnetic field lines do not intersect each other at any point.
- Inside the magnet, the direction of field lines is from its south pole to its north pole.
- Closer magnetic field lines indicates the region of stronger magnetic field while widely separated magnetic field lines represent weaker magnetic field. It means magnetic field is stronger at poles of the magnet.
- The tangent at any point on the magnetic field lines gives the direction of the magnetic field at the point.
- The magnetic field lines are closed curves.
Question 3.
Why don’t two magnetic field lines intersect each other?
Answer:
Two magnetic lines of force do not intersect each other because if they intersect, then there would be two directions of magnetic field at one point, which is not possible.
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 diagram of the magnetic field inside and outside the circular loop (by applying right hand thumb rule) is shown below.
are shown dotted and they are perpendicular to the plane of paper. The face of loop (front – side) is the south pole and back face (on the table) is a north pole.
Question 2.
The magnetic field in a given region is uniform. Draw a diagram to represent it.
Answer:
In uniform magnetic field the magnetic field lines are parallel and equidistant, as shown in figure.
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.
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) and (d) when a proton moves in a magnetic field, a magnetic force acts on it. This causes the path of the proton to become circular. Hence, both its velocity and momentum changes.
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:
According to
F = IBl
- If the current (I) in the rod AB is increased, force F also increases.
- When a stronger horse – shoe magnet is used, magnetic field B increases, thus force F also increases.
- If the length (l) of the rod is increased, force F also 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:
(d) Direction can be known by Fleming’s left hand rule.
Page 233.
Question 1.
State Fleming’s left – hand rule.
Answer:
Stretch the fore finger, middle finger and the thumb of left hand mutually perpendicular to each other. If the fore finger indicates the direction of the magnetic fields and the middle finger indicates the direction of current, then the thumb indicates the direction of the motion of the conductor, i. e. force on conductor. This is Fleming’s left – hand rule.
Question 2.
What is the principle of an electric motor?
Answer:
When a current – carrying conductor or coil placed in magnetic field then it experiences a force which causes it to move.
Question 3.
What is the role of the split ring in an electric motor?
Answer:
In electric motors, the split ring acts as a commutator. This reverse the direction of flow of current through a circuit. Due to this there is a constant rotation of the coil and the axle.
Page 236.
Question 1.
Explain different ways to induce current in a coil.
Answer:
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 the magnetic field.
Page 237.
Question 1.
State the principle of an electric generator.
Answer:
The principle of an electric generator is based on the phenomenon of electromagnetic induction, which is, “When a coil is rotated in a magnetic field, there is a change in the magnetic field lines passing through the coil, due to which the induced current in the coil is generated.”
Question 2.
Name some sources of direct current.
Answer:
Cells, batteries and DC generator.
Question 3.
Which sources produce alternating current?
Answer:
AC generators.
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.
Page 238.
Question 1.
Name two safety measures commonly used in electric circuits and appliances.
Answer:
- Fuse
- Earth wire.
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:
Given, P = 2 kW = 2000 W,
V = 220 V,
P = VI
I = p/v = 2000/220
Thus = 9.09 Ampere.
As the current rating of the circuit given is 5A and the current flowing through it is more i.e. 9A, hence, the fuse in the circuit melts and circuit is broken.
Question 3.
What precaution should be taken to avoid the overloading of domestic electric circuits?
Answer:
Precautions to avoid overloading are:
- Electrical circuit should be divided into different sections and each appliance should have fused.
- The wires used for electric current should be covered with good resistance material.
- High power appliances such as fridge, air-conditioner, water heater, press, etc. should not be used together.
- Do not use too many electrical appliances from the same socket.
- Electrical appliances with faults should not be used.
RBSE Class 10 Science Chapter 13 Magnetic Effects of Electric Current Textbook Questions and Answers
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 centred on the wire.
Answer:
(d) The field consists of concentric circles centred on the wire.
Question 2.
The phenomenon of electro – magnetic 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) producing induced current in a coil due to relative motion between a magnet and the coil.
Question 3.
The device used for producing electric current is called?
(a) generator.
(b) galvanometer.
(c) ammeter.
(d) motor.
Answer:
(a) generator.
Question 4.
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) 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) increases heavily.
Question 6.
State whether the following statements are true or false.
(a) An electric motor converts mechanical energy into electrical 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 of an electric supply.
Answer:
(a) False
(b) True
(c) True
(D) False.
Question 7.
List two methods of producing magnetic fields.
Answer:
- There is a magnetic field around a permanent magnet.
- A magnetic field is present around a current – carrying straight wire.
Question 8.
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 coil of many circular turns of insulated copper wire wrapped closely in the shape of a cylinder is called a solenoid. When electric current is passed through a solenoid, then this rod generates a magnetic field around it and behaves like a magnet. A current – carrying solenoid is equivalent to a bar magnet. Its polarities at ends is depend upon the direction of current flowing through it.
To determine the polarities of its ends, place it in a brass hook and suspend it with a long thread. By bringing a bar magnet near it and pointing the north pole of bar magnet near one of the ends of solenoid, if solenoid moves towards the bar magnet then that end of solenoid is a south pole. If solenoid moves away from the magnet, then the encl of solenoid is its north pole.
Question 9.
When is the force experienced by a current – carrying conductor placed in a magnetic field largest?
Answer:
The force on a current – carrying conductor placed in a magnetic field is largest when the direction of the electric current is at right angle to the dir ection of the magnetic field.
Question 10.
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 d irection of magnetic field?
Answer:
The direction of magnetic field can be known by the Fleming’s left hand rule. According to it, the direction of magnetic field, the direction of current and the direction of motion, all are perpendicular to each other. As the electron is moving towards front wall, so direction of current will be towards the back wall. Also, the beam is deflected to the right side, the force will be on lower side. Applying Fleming’s left hand rule, it is clear that magnetic field (B) is acting vertically downwards.
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: An electric motor works on a principle that when electric current passes through it, it converts, electrical energy into mechanical energy.
Construction: An electric motor, as shown in figure consists of a rectangular coil ABCD of insulated copper wire. The coil is placed between the two poles of a magnetic field such that the arm AB and CD are perpendicular to the direction of the magnetic field. The ends of the coil are connected to the two halves P and Q of a split ring. The inner sides of these halves are insulated and attached to an axle. The external conducting edges of P and Q touch two conducting stationary brushes X and Y, respectively, as shown in the figure.
Working: Current in the coil ABCD enters from the source battery through conducting brush X and flows back to the battery through brush Y. The current in arm AB of the coil flows from A to B. In arm CD it flows from C to D, that is, opposite to the direction of current through arm AB. On applying Fleming’s left hand rule for the direction of force on a current-carrying conductor in a magnetic field. We find that the force acting on arm AB pushes it downwards while the force acting on arm CD pushes it upwards.
Thus the coil and the axle O, mounted free to turn about an axis, rotate anti – clockwise. At half rotation, Q makes contact with the brush X and P with brush Y. Therefore the current in the coil gets reversed and flows along the path DCBA. In electric motors, the split ring acts as a commutator. The reversal of current also reverses the direction of force acting on the two arms AB and CD. Thus the arm AB of the coil that was earlier pushed down is now pushed up and the arm CD previously pushed up is now pushed down.
Therefore the coil and the axle rotate half a turn more in the same direction. The reversing of the current is repeated at each half rotation, giving rise to a continuous rotation of the coil and to the axle. Function of Split Rings Split rings rotate with the coil and reverse the direction of current flowing through the coil every time the coil just passes the vertical position during a revolution.
Question 12.
Name some devices in which electric motors are used.
Answer:
Mixers, grinders, washing machines, electric fans, electric coolers, refrigerators 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) withdrawn from inside the coil, (iii) held stationary inside the coil?
Answer:
(i) When a bar magnet is pushed into the coil, the magnetic flux linked with the coil changes (increases). Due to change in flux, an induced current flows in the coil and the galvanometer will show a momentary deflection in one side.
(ii) When bar magnet is withdrawn from inside the coil, this time also there is change of magnetic flux in the coil (decreases). Due to this change in flux induced current flows in the coil, but the direction of induced current is opposite to first case. This time galvanometer again shows a momentary deflection but in the opposite direction of previous one.
(iii) When the magnet is held stationary in the coil, the magnetic flux linked with the coil remains constant. Due to this there is no flow of any induced current in the coil and galvanometer shows no deflection.
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:
Due to changing current in the coil A, a current will be induced in the coil B which is placed close to A. The reason of induced current flows is that magnetic flux linked with A also get linked with B due to its being close to A. When the current in A changes, the magnetic flux linkages with A change. Due to this, the flux linkages with B also change. As a result of this, current is induced in the coil B.
Question 15.
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) Right Hand Thumb Rule: If we hold a conductor in such a way that the stretched right hand thumb is along the direction of current then the direction of curl of fingers around the conductor gives the direction of the magnetic field.
(ii) Flemings Left Hand Rule: According to this rule, stretch the thumb, forefinger and middle finger of your left hand such that they are mutually perpendicular (figure). 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.
According to this rule, if we stretch our right hand in such a way that forefinger, middle finger and thumb are mutually perpendicular, then thumb will give direction of motion, forefinger gives direction of magnetic field (B) and middle finger gives the direction of induced current – I.
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: Alternating current generator is based upon the principle of electromagnetic induction. When a closed coil is rotated rapidly in a strong magnetic field, the number of magnetic flux lines passing through the coil changes continuously. Hence, an emf is induced in the coil and a current starts flowing in it. In fact, the mechanical energy expanding in rotating the coil appears as electrical energy (current) in the coil
Construction: The main parts of an AC generator are as follows:
- Armatur: It is rectangular coil having a large number of turns of insulated copper wire wound over a soft – iron core. The increases the magnetic flux linked with the armature.
- Field Magnet: It is a powerful electromagnet having concave pole – pieces N and S. The armature is rotated between these pole – pieces about an axis perpendicular to the magnetic field lines.
- Slip Rings: The leads from the armature coil are connected to two copper rings R1 and R2 called the ‘slip rings’. These rings are concentric with the axis of the armature coil and rotate with it.
- Brushes: These are two carbon pieces B1 and Br called ‘brushes’, which remains stationary pressing against the slip rings R1 and R2 respectively. The brushes are connected to the external circuit in which current is to be supplied, by generator.
Working:
As the armature – coil rotate, the magnetic flux lines passing through the coil changes. Hence, an emf is induced in the coil.and a current starts flowing in it. Suppose the coil is rotating clockwise and is horizontal at any time. At this time, the arm AB of the coil is moving up and the arm CD is moving down. By Fleming’s right – hand rule the current flows from A to B in the arm AB and from C to D in the arm CD.
The brush Bl at which the current is entering the external circuit is positive relative to the brush B2 at which the current is leaving the external circuit. As the coil rotates from its vertical position, the arm AB moves down and the arm CD moves up. Hence the direction of the current in the coil reverses. The brush B2 is now positive relative to Bv Thus, an alternating potential difference is developed between B1 and Bv generating an alternating current in the circuit.
Function of Brushes: The two copper pieces B1 and B2 attached to the split rings R1 and R2 in an electric generator are called brush. They changes the direction of current in the external circuit after every half round the rotating coil.
Question 17.
When does an electric short circuit occur?
Answer:
Electric short – circuit occurs when both live wire and neutral wire come in contact to each other. The phenomenon of short circuit occurs when either the wire is not properly insulated or there is a fault in the electric appliance.
Question 18.
What is the function of an earth wire? Why is it necessary to earth metallic appliances?
Answer:
Earthing is the system of connecting the metal casing of an electric appliance with a copper plate buried deep inside the earth. It is used to prevent the electrical shock from electric appliance. When the plastic insulation of live wire is damaged it touches the metal case and when any person touch it with bare hands, he receives a shock.
To avoid this, metal casing is earthed in which one end of wire is connected to the metal body of appliance and other end connected to a copper plate buried deep inside the earth. When live wire accidentally touches the metal body then the electric current flows from appliances to earth through copper wire and a heavy current flows towards earth and protect the person from electric shock.
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