# Class-10 Goyal Brother Electromagnetism ICSE Physics Ch-10 Magnetic Effects and Induction

Class-10 Goyal Brother Electromagnetism ICSE Physics Ch-10 Magnetic Effects & Induction. We Provide Step by Step Answer of Exercise, MCQs Questions of Exercise-1 & 2. Goyal Brothers Electromagnetism ICSE Class-10 . Visit official Website CISCE  for detail information about ICSE Board Class-10 Physics.

## Class-10 Goyal Brother Electromagnetism ICSE Physics Ch-10 Magnetic Effects & Induction

-: Select Topics :-

Exercise-1

MCQ -1

Exercise-2

MCQ -2

### Exe-1

Electromagnetism

Class-10 Goyal Brother Magnetic Effects of Electric Current and Electromegnetic Induction

Page-175,176

Question 1.
When can an electric charge give rise to a magnetic field?
When electric charge is in motion e. charge flows, it gives rise to magnetic field.

Question 2.
Describe Oersted’s experiment to show that a conductor carrying current produces a magnetic field around it
Oersted’s Experiment :
Set up the apparatus as shown in fig. when switch is in open circuit

magnetic needle points in north direction. Showing there is no magnetic field around it. Now when switch is closed and current flows through the wire, the magnetic needle gets deflected from north. This shows that conductor carrying current produces magnetic field around it and deflects the magnetic needle.

Question 3.                Class-10 Goyal Brother Electromagnetism
(a) How will you plot the magnetic field lines around a straight conductor carrying current ?
(b) State two rules by which you can determine the direction of the magnetic field around a straight conductor.
(a) To plot the magnetic field lines around a straight conductor carrying current: Pass straight conductor through a cardboard or glass-plate. And pass current.

From A to B direction in the upward direction. Sprinkle iron filings on glass plate. Tap the glass plate, the iron filing will arrange themselves in circles around the conductor along the magnetic lines of force. The magnetic fields are circular in nature. The direction of magnetic field can be detected with the help of magnetic compass and direction is found anti clock wise.

(b) Two rules are :

1. Right hand thumb rule: “Imagine you are holding the current carrying wire in your right-hand so that your thumb points in the direction of current, then the direction in which your fingers encircle the wire will give the direction of magnetic field lines around the wire.”
2. Max Well’s Screw Rule : “Imagine driving a cork screw in the direction of current, then the direction in which we turn its handle is the direction of magnetic field (or magnetic field lines).

Question 4.
(a) Draw a set up for plotting magnetic field around a circular coil carrying current.
(b) State the properties of the magnetic field in 4(a).
(a)

(b) Properties of the magnetic field :

1. The magnetic field lines are circular near current carrying loop.
2. At the center of the circular loop the magnetic field lines are in the same direction and strength of magnetic field increases.

Question 5.
What is a solenoid ? Draw a magnetic field around a solenoid, when direct current flows through it. How will you find the magnetic polarity of a solenoid without using a magnetic needle ?
Solenoid : “Is a long coil containing a large number of close turns of insulated copper wire.”

Magnetic polarity of solenoid can be determined like a bar magnet i.e. when it is suspended freely, it will come to rest pointing in North and South direction or polarity can be checked by bringing north pole of a bar magnet. The pole repelled by north pole must be North pole of solenoid.

Question 6.
How does the magnetic field set up in a solenoid changes when:
(a) number of turns are increased ?
(b) diameter of the solenoid is increased ?
(c) strength of the current is increased ?
(d) a soft iron core is placed in it ?

(a) When number of turns are increased magnetic field will be stronger.
(b) When diameter of the solenoid is increased but diameter should be less than the length of solenoid, so that parallel lines should add up to give a stronger field.
(c) When strength of current is increased stronger will be the magnetic field produced.
(d) When soft iron core is placed in the solenoid very strong magnetic field is produces.

Question 7.
Give four differences between an electromagnet and a permanent magnet.
Differences between electromagnet and permanent magnet:
Electromagnet:

1. It is temporary magnet
2. It strength can be changed, by changing the current.
3. Polarity can be changed by changing the direction of current.
4. Produces very strong magnetic force.

Permanent Magnet

1. It is permanent magnet.
2. It strength cannot be changed.
3. Polarity cannot be changed.
4. Produces weak magnetic force.

Question 8.                            Class-10 Goyal Brother Electromagnetism
State four practical applications of electromagnets.
Four applications of electromagnet :

1. In electric bell.
2. In magnetising steel bars.
3. For scanning machines (MRI)
4. In electric motor, generator.

Question 9.
(a) On what factors does the force experienced by a straight conductor placed in a magnetic field depend
(b) State the law which determines the force experienced by a conductor.
(a) Factors on which force experienced by a straight conductor depend :

1. Current passing : direct proportional to current passing.
2. Inversely proportional to the distance of that point from the wire.

(b) When a conductor carrying current is placed in a magnetic field in a direction other them the direction of magnetic field, experiences a force called Lorentz force. This force is perpendicular to both, the direction of current I and the direction of magnetic fields B.
This law is called :
Fleming’s left hand rule : “Stretch the fore finger, control finger and the thumb of your left hand mutually perpendicular to each other. If the fore-finger points in the direction of magnetic field, central finger indicates the direction of current, then the thumb will indicate the direction of motion of conductor (i.e., force on conductor)

Question 10.
(a) Draw a neat and labelled diagram of a d.c. motor and explain its construction and working.
(b) How can you make a d.c. motor more powerful ?
(c) How can you convert its jerky motion into uniform circular motion ?
(a) D.C. Motor

Construction : A d.c. motor consists of :

1. Rectangular coil ABCD of insulated copper wire moved between two Horse shoe
2. Permanent magnet M such that AB and CD are perpendicular to the magnetic field.
3. Two half rings (commutators) of copper X, Y are soldered to ends A and D of coil to change the direction of current flowing after every half rotation of the coil.
4. Two carbon brushes P and Q fixed to the base of motor keep pressing highly against commutators. Battery to supply the current to coil is connected to the coil. The function of brushes is to make contact with the rotating rings of  the commutator and through them to supply current to the coil.

Multiple Choose Questions-1

## Class-10 Goyal Brother Electromagnetism ICSE Physics Ch-10 Magnetic Effects & Induction

1. A wire carrying a current is held over a freely suspended magnetic needle, such that the current in the wire flows from south to north. The direction in which the north end of freely suspended magnetic needle will point towards.
(a) West
(b) East
(c)South
(d) North

2. In an electric motor :
(a) mechanical energy changes to heat energy
(b) mechanical energy changes to electric energy
(c) electric energy changes to mechanical energy.
(d) electric energy changes to magnetic energy

3. By reversing the direction of current in an electromagnet, the magnetic field produced by it
(a) increases in strength
(b) remains unchanged in strength and direction
(c) gets reversed in direction
(d) decreases in strength

4. The power of a d.c. motor can be increased :
(a) by increasing number of turns in its coil
(b) by laminating its soft iron core
(c) by increasing the strength of current flowing through it
(d) all of these

5. Commutator is a device in a d.c. motor which :
(a) increases the power
(b) reverses direction of current coil after full rotation of coil
(c) reverses direction of current after half rotation of coil
(d) increases the strength of electromagnet

6. Which is not the use of an electromagnet ?
(a) Used in electric appliances such as electric bell and electric fans.
(b) Used for magnetising steel bars.
(c) Used for making sensitive magnetic compass.
(d) Used in separating iron particles from a scrap of iron and other metals.

7. Which is not the property of a solenoid ? The magnetic field of solenoid can be increased
(a) by increasing the number of turns in the solenoid.
(b) by increasing the strength of current flowing through the solenoid.
(c) by placing a stainless steel core within the solenoid.
(d) by placing a laminated soft iron core within the solenoid.

### Exe-2

Electromagnetism

Class-10 Goyal Brother Magnetic Effects of Electric Current and Electromegnetic Induction

Page-185,186

Question 1.
State Faraday’s laws of electromagnetic induction.
Faraday’s Laws of Electromagnetic Induction :

1.  When ever there is a change in the magnetic flux linked with a coil an e.m.f. is induced. The induced e.m.f. lasts as long as the change lasts (i-e-, there is a change in the magnetic flux linked with the coil.
2. The magnitude of the e.m.f. induced is directly proportional to the rate of change of the magnetic flux linked with the coil. If the magnetic flux changed at a fixed rate, a stready e.m.f. is produced.

Question 2.
State
(a) Fleming’s right hand rule,
(b) Lenz’s law for finding the direction of induced current. Which of the above laws is most suitable for finding the direction of current in

1. straight conductor
2.  coiled conductor ?

(a) Fleming’s right hand rule:

Or

(1) Generator rule : “Stretch the thumb, fore finger and central finger of right hand mutually perpendicular to each other. If the fore finger indicates the direction of magnetic field and thumb indicates the direction of motion of the conductor then central finger will indicate the direction of induced current.”

(2) Lenz’s Law : “The direction of induced e.m.f. (or induced current) always tends to oppose the cause which produces it.”

(a) In straight conductor — Fleming’s Right Hand Rule
(b) in coiled conductor — Lenz’s Law.

Question 3.                            Class-10 Goyal Brother Electromagnetism
What do you understand by the term mutual induction ? Describe an experiment in support of your answer.
Mutual induction: “The phenomenon of production of induced e.m.f. in a closed coil, by varying the magnetic flux in another coil is called mutual induction.”
Experiment :

P(primary coil) behaves as electro magnet when current passed by opening and closing the switch and pointer of the secondary coil (s) shows deflection proving that induced e.m.f. is produce in secondary coil. As soon as the switch is off (open circuit) deflection stops in secondary coil.

Or

The induced e.m.f. can be generated in the secondary coil, by placing the primary coil permanently in the secondary coil, and rapidly closing and opening the switch closing switch amounts to increases in magnetic flux in the primary coil, and hence in the secondary coil. Opening the switch amounts to decrease in magnetic flux in the primary and the secondary coil. Thus induced e.m.f. is generated in secondary coil.

Question 4.
What do you understand by the terms (a) self induction (b) eddy current ?
(a) Self induction: “The phenomenon due to which a current flowing through a part of coil, induces an e.m.f. in the rest of coil due to change in magnetic flux is called self induction.”

(b) Eddy currents : “The current produced in any metallic conductor when a magnetic flux is changed around it is called Eddy Current.

Question 5.
(a) Describe with the help of a clear diagram the structure of a.c. transformer, suitable for lighting 12 V lamp from 240 V mains.
(b) Explain how a transformer reduces emf ?
(c) Why are transformers so important for the transmission of energy ?
(a) We are to transformer for lighting 12V lamp from 240 V mains.
Therefore step down transformer is needed.
The magnitude of induced e.m.f. is produced by the formula.

Primary coil:

• It should have 20 times more number of turns as compared to secondary coil.
• It is made of thinner copper wire.
• It should be more heavily insulated secondary coil.

Secondary coil :

• It should be made of thicker copper wire.
• It should be less heavily in solated.

(b) The number of turns in secondary 1/20 of the number of turns in primary coil reduces the e.m.f. to 1/20  th e.m.f. of primary coil.
(c) Transformers are important for transmission of energy. The power from the generating station is transmitted over long distances at a voltage higher than 11 kv to minimise the loss of energy in form of heat in the line wires used for transmission for this step up transformer is used which step up 11 kv to 132 kv at the generating station. To transmit if to industries it is stepped down to 33 kv using step down transformer. Further stepped down to 11 kv to transmit to light industry. It is further stepped down to 220 V by step down transformer to supply it to domestic consumers.

Question 6.                        Class-10 Goyal Brother Electromagnetism
(a) Draw a labelled diagram of an a.c. generator.
(b) Why is the emf produced by an a.c. generator zero at a certain instant and reaches the maximum value at the other instant?
(c) The efficiency of a generator is never 100%. Explain.
(a)

(b) The e.m.f. produced by a.c. generator is zero when magnetic flux linked with coil is maximum. This happens when the plane of coil is normal to the magnetic field.

(c) The efficiency of a generator is never 100% because

1. a part of energy is wasted due to magnetic hysteresis.
2. A part of energy is wasted an account of the resistance of primary and secondary coils wound around the core
3. A part of current is wasted on account of the Eddy currents formed with in the soft iron core.

Question 7(a) .
The adjacent diagram 10.44 shows a movable permanent magnet and fixed copper coil of many turns, connected to a center zero galvanometer.

1. The magnet is rapidly moved in the direction of the arrow.
2. The magnet is stopped within the coil
3. The magnet is then pulled out rapidly.

Question 7(b).
What will be your observations, if a more powerful magnet is used ?
(1)

(1) A momentary deflection of pointer of galvanometer towards right side is seen.
(2) More the speed, more is the deflection.
(3) When magnet is stopped with in the coil, the pointer of galvanometer comes to zero position.
(4) Deflection of pointer of galvanometer is in opposite direction to towards the left.

(2)  Then more powerful magnet is used deflection of pointer will be more.

Multiple Choose Questions-2

## Class-10 Goyal Brother Electromagnetism ICSE Physics Ch-10 Magnetic Effects & Induction

1. The direction of current in a conductor can be obtained by ?
(a) Fleming’s right hand rule
(b) Fleming’s left hand rule
(c) Right hand thumb rule
(d) Maxwell’s cork-screw rule

2. In a step down transformer :
(a) number of turns in primary coil are less than the secondary coil.
(b) number of turns in primary coil are more than the secondary coil.
(c) number of turns in primary coil are equal to the secondary coil
(d) the primary and secondary coils are wound on separate steel cores.

3. Step up transformers are used:
(a) for long distance transmission of power
(b) for distribution power in localities.
(c) for saving sensitive appliances, such as T.V andA.C.
(d) any of these

4. Which is the incorrect statement ? In a step down transformer
(a) number of turns in primary are more than the secondary coil
(b) the primary coil is thinner as compared to the secondary coil.
(c) the primary coil is thicker as compared to secondary coil.
(d) the primary coil is more heavily insulated as compared to secondary coil

5. In an cue. generator the magnitude of induced current can be increased by :
(a) increasing number of turns in the coil
(b) increasing the area of cross-section of the coil
(c) increasing the strength of field magnets
(d) all of these

-: End of Goyal Brother : Electromagnetism ICSE Physics Ch-10  Solution :-