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Armature: Armature is a coil that consists of a large number of turns of insulated copper wire wound over a soft iron core. it revolves around an axle between two poles of a strong magnet.

Short circuiting: When live wire and neutral wire come in direct contact, the resistance of the wire becomes very small. Then huge current flows through the circuit and produces a large amount of heat in the circuit and the circuit catches fire. This is known as short circuiting.

In AC generator, ends of coil are connected to two slip rings.

In DC generator ends of coil are connected to two half split rings.

Electric generator: It is a device that converts mechanical energy into electrical energy.

Instead of two slip rings, we have to use a slip ring commutator to change A.C. generator into a D.C. generator

By connecting two half-slip rings instead of a slip ring commutator on either side to the ends of the coil we can get D.C. current.

1) The law behind the making of ‘generator’ is Faraday’s law. 

2) Faraday’s Law : 

“Whenever there is a continuous change of magnetic flux linked with a closed coil, a current is generated in the coil”.

B) 1 Weber/meter²

1. Place a compass needle underneath a wire and then turn on electric current.

2. Immediately the needle of compass shows the deflection. By this we can conclude that electricity and magnetism are related phenomena.

Correct option is  A) Oersted

C) F = qvBsinθ

We can produce magnetism from electronic current. Ampere with his Ampere’s swimming rule explained the direction of electric current and the deflection of magnetic needle.

1. If a person touches the live wire, he gets severe shock which may prove fatal.

2. Short-circuiting can cause a spark which may lead to fire in a building.

Zero, because neutron is charge less particle.

Correct option is  A) qvB

Correct Answer is: (a) BAN/L 

ϕ = Li = BAN.

Correct Answer is: (a, b)

Current in AB and CD causes magnetic fields in the same direction on T, upward in this case. Hence there is a net magnetic field over T.

Correct Answer is: (b) contract

Treat the gas as a thick conductor carrying a uniform current. Apply Ampere’s law to find the magnetic field. Then apply the left-hand rule to find the direction of the Ampere force. 

Correct Answer is: (a, c)

Apply the definition of 1 ampere. 

Correct Answer is: (a) zero only at the centre of the loop 

The resistance of AD is one-third of the resistance along the parallel path AB + BC + CD. Hence if current i enters at A, 3i/4 will flow along AD and i/4, along AB. The magnetic field at the centre due to AD is equal and opposite to the combined effects of AB, BC and CD.

Correct Answer is: (a) due to the straight conductors is zero, (b) due to the loop is zero 

Correct Answer is: (c) has different magnitudes at different points

The sections AB and CD produce fields in the same direction at all points on BC. The magnitude of the field is variable, being a function of the distances from AB and CD.

At the midpoint of BC, B = 2 x  μ₀I/4π(d/2).

Correct Answer is: (a) upward 

Correct Answer is: (b)

The magnetic field of solenoid can be increased by the following two ways. 

1. by increasing the number of turns of winding in the solenoid. 

2. by increasing the current through the solenoid.

1. Fix a white paper on a wooden plank. 

2. Make two holes to the plank at appropriate distance.

3. Make some more holes parallel to these two holes. 

4. Insert a copper wire through these holes. It looks as a coil. 

5. Connect the two ends of the coil to a battery and a switch in series. 

6. When swich is on current flows through the wire. 

7. Sprinkle some iron filings around the coil and tap the plank. 

Observation : 

An orderly pattern of iron filing is seen on the paper. These are magnetic field lines. The magnetic field lines set up by solenoid resemble those that of a bar magnet.

E.M.F = \(\frac {-Δϕ}{Δt}\), but both moving same direction, so change in flux linked with coil is zero i.e., ∆Φ = 0

1. Moving a north pole of a magnet into a coil. 

2. Withdrawing north pole from a coil. 

3. Moving a south pole of magnet into a coil. 

4. Withdrawing a south pole of a magnet from a coil. 

5. Moving a coil towards a magnet.

1)  The magnetic field lines due to current carrying solenoid are identical to those of bar magnet. Thus a current carrying solenoid behaves just like a bar magnet with fixed polarities at the ends. The end at which the direction of current is clockwise behaves like a south pole and the end at which current is anti-clockwise behaves like a north pole.

2)  A current-carrying solenoid when suspended freely, will set itself in the north south direction exactly in the same manner as a bar magnet does. 

3)  A current-carrying solenoid also acquires the- attractive property of magnet. If iron filings are brought near the solenoid, it attracts them when current flows through the solenoid.

The needle of compass will deflect as the wire carrying current is associated with magnetic field.

Two ADVANTAGES OF ELECTROMAGNETIC OVER PERMANENT MAGNET are : 

1. Its strength can be increased or decreased by increasing or decreasing current. 

2. It loses magnetism as soon as current is stopped and acquires magnetism as soon as current is passed. 

3. The polarity can be changed by changing the direction of current. 

4. It produces stronger magnetic field. 

When current carrying conductor is wound over a magnetic material like soft iron it gets magnetized.

An electromagnet acquires the magnetic properties only when electric current is passed through the solenoid. Once the current is switched off, it almost loses its magnetic properties as retentivity of soft iron is very low. The strength of the electromagnet depends upon number of turns per unit length of the solenoid and the current through the solenoid.

In electric generators and televisions

Four applications of electromagnet : 

1. In electric bell. 

2. In magnetising steel bars. 

3. For scanning machines (MRI) 

4. In electric motor, generator.

We get mechanical energy from electric motor.

In our daily life we use motor in 

i) Mixies 

ii) Grinders 

iii) Water Pumps 

iv) Fans / Coolers, etc.

When a rectangular coil is placed in magnetic field and current is passed through it, two equal and opposite forces act on the coil which rotates it continuously.