Electromagnetism – Physics10

Ans: Righthand rule: According to Fleming’s left hand rule grasp a wire your right hand such that your thumb is pointed in the direction of current. Then curling fingers of your hand will point in direction of magnetic field.

Q.2 Define Electromagnetism.

Ans. Electromagnetism: Electromagnetism is the study of magnetic effect of current. The uses of electromagnetism are different fields of science and technology is very wide. Motors and electric meters are based on the effect of magnetism.

Q.3 What is magnetic resonance imaging (MRI)?

Ans. Weak ionic current in our body that travels along the nerve can produce the magnetic effect. This forms the basis of obtaining images of different parts
of body. This is done using the technique called magnetic resonance imaging (MRI).

Q.4 Describe the method to find the direction of magnetic lines of force produced by current carrying solenoid.

Ans. The direction of the field produced by a coil due to flow of conventional current can be found with ‘the help of right hand grip rule. According to this rule:

“If we grip the coil with our right hand by curling our fingers in the direction of the conventional current, our thumb will indicate the north pole of the coil”

Q.5 Which device is used for converting electrical energy into mechanical energy and at what principle it works?
Ans: A D.C motor is a device that converts direct current (electrical energy) into mechanical energy.

Principle: When .current carrying coil is placed in a magnetic field, it experiences a couple due to which the coil begins to rotate. A D.C motor operates on this principle.

Q.6 What is the fundamental difference between generator and motor?

Ans. Generator: Generator is a device that converts mechanical energy into electric energy.
Motor: Electric motor is a device that converts electric energy into mechanical energy.

Q.7 Define electromagnetic induction.

Ans. Electromagnetic Induction: The process of generating an induced current in a circuit by changing the number of magnetic lines of force passing through it is called electromagnetic induction.

Q.8 State the Faraday’s law of electromagnetic induction.
Ans: Faraday’s law: The value of induced e.m.f in a circuit is directly proportional to rate of change of number of magnetic lines of force through it.

Q.9 Define strength of magnetic field.

Ans. Strength of magnetic field: The strength of magnetic field is defined as the number of magnetic lines of force passing through any surface.

Q.10 Define A.C. generator.

Ans. A.C. Generator: A.C. generator, which is a device that converts mechanical energy into electric energy.

Q.11 State the principle of A.C.

Ans. Principle of A.C. When a coil rotates in a magnetic field, the induced current in it continuously changes from maximum to minimum value and from minimum to maximum value and so on. This is the basic principle on which an A.C. generator works.

Q.12 What is mutual induction?

Ans. Mutual Induction: The phenomenon of production of induced current in one coil due to change of current in a neighboring coil is called mutual induction.

Q.13 How many coils are used in a Transformer? Also write their names.

Ans. A transformer has two coils.

i) Primary Coil ii) Secondary coil

Q.14 Can transformer work on direct current?

Ans. No, a standard transformer cannot work with direct current.

Reason: The primary coil has to induce current in the secondary coil. The only way this can happen if there is a varying magnetic field in primary which then will induce a varying magnetic field in secondary which results in a current in the secondary. Only varying (alternating current) current can

induce a varying magnetic field .

Q.15 Define electromagnetic. How many poles it has?

Ans. Electromagnetic: The type of temporary magnet, which is created when current flows through a coil, is called an electromagnet. It has two poles (North pole, South pole).

Q.16 How can we find the direction of magnetic field by using right hand rule?

Ans. Right hand rule:

According to this rule grasp a wire with your right hand such that your thumb is pointed in the direction of current. Then curling fingers of your hand will point in the direction of the magnetic field.

Q.17 What is meant by solenoid?

Ans. Solenoid: A long coil of wire consisting of many loops is called a solenoid. The field from each loop in a solenoid adds to the field of the other loops sand creates greater total fields strength.

Q.18 How the direction of magnetic lines field are determined in current carrying straight wire?

Ans. The directions of the magnetic lines field are determined in current carrying straight wire by” right hand grip rule. “Grasp a wire with your right hand such that your thumb pointed in the direction of current then curling fingers of the hand will point out the direction of magnetic field.”

Q.19 Write down two ways to increase the magnetic field.

Ans. i) The current in the wire is increased.

ii) Strength of magnetic field is increased.

Q.20 Define Fleming’s left hand rule.

Ans. Fleming’s left hand Rule: According to this rule stretch the thumb, forefinger and the middle finger of the left hand mutually perpendicular to each other. If the forefinger points in the direction of the magnetic field, the middle finger in the direction of the current, then the thumb would indicate the direction of the force acting on the conductor.

Q.21 What is meant by electric motor?

Ans. Electric motor: Electric motor is a device that converts electric energy into rotational kinetic energy.

Principle: Torque acting on a loop placed in the magnetic field, is proportional to the magnetic of current passing through the loop. If we increase the number of loop, the turning effect greatly increased. This is the principle of electric motor.

Q.22 What is the function of split rings commutator in D.C motor?
Ans. The function of split rings commutator in D.C. motor is reversal of direction of current. The connection to coil is made through an arrangement of brushes and split rings.

Q.23 Why reserves the direction of electric current in the armature coil of D.C. motor?

Ans. Brushes, which are usually pieces of graphite, make contact with the commutator and allow current to flow into the loop. As the loop rotates,” so does the commutator. The split ring is arranged so that each half of the commutator changes brushes just as the coil reaches the vertical position changing brushes reverse the current in the loop.

Q24. What is meant by armature?

Ans. Electric motor is consists of many loops mounted on a shaft or axle. This coil is called an armature. The torque on the armature, and as a result, the speed of motor, is controlled by varying the current through the motor.

Q.25 What are the factors which affect the magnitude of the e.m.f induce, a circuit by changing magnetic field?

Ans. The magnitude of induced e.m.f. in a circuit depends on the following factors:

i) Speed of relative motion of the coil and the magnet.
ii) Number of turns of the coil.

Q.26 Define Lenz’s law.
Ans. Lenz’s law: According to this law the direction of an induced current circuit is always such that it opposes the cause that produces it.

Q27. Why voltages produce when conductor moved in magnetic field?
Ans: When a conductor move in magnetic field. The magnetic lines of change which cause induced voltages.

Q.28 What is use of Transformer and how many coils it consist?

Ans. i) Transformer

Transformers are used to increase or decrease AC voltages. Usage transformers is common because they change voltages with relatively little loss of energy.

ii) Number of coils in Transformer
A transformer has two followings coil.

a) Primary Coil b) Secondary coil

Working Principle of Transformer

Transformer work on the principle of mutual induction.

Q.29 What is meant by Relay?
Ans. Relay: The relay is used to control a large current with the help of a small current.

Working of Relay: It works on the principle’ of electromagnet.