Magnetic Effects of Electric Current Test - 12

(1) The tesla (symbolized T) is the standard unit of magnetic flux density.
(2) A solenoid is a tightly wound helical coil of wire whose diameter is small compared to its length. The magnetic field generated in the centre, or core, of a current carrying solenoid is essentially uniform, and is directed along the axis of the solenoid.
(3) The needle of a magnetic compass is 'just' a small bar magnet that is balanced carefully so it can rotate freely.
(4) Solenoid is temporary strong magnet, when connected through external source like battery or when electricity passed through it. It is also known as electromagnet.

1. A lodestone is a naturally magnetized piece of the mineral magnetite. Loadstone is iron ore.
2. Magnetic flux is the number of magnetic field lines passing through a surface placed in a magnetic field.
3. An electric motor converts electrical energy into mechanical energy.
4. Permanent magnet are usually made of hard materials which are strongly magnetized. A perfect example of permanent magnet is the Bar Magnet. In fact, Permanent magnets are most of the times referred to as Bar Magnets also.

Like poles repel each other and unlike poles attract each other. Live wire is red in colour and neutral wire is black in colour.

The magnitude of the magnetic field produced at a given point is directly proportional to the magnitude of the current passing through the conductor. Strength of the field at any point is inversely proportional to the distance of the point from the wire. ( B ∝I and B ∝ 1/r )

A. Acurl is always present when a field line forms a closed loop.
B. The voltage of the neutral wire is always zero.
C. AC power transmission losses are greater than DC losses.
D. Fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit.
So, statements (A), (B) and (C) are correct.

A. A fuse wire is a safety wire connected in series with the live wire, in case of any large current supply or malfunctioning in the electric connections it melts and breaks the electric circuit.
B. A fuse wire is connected in series so as to pass the current totally through the fuse. It is not  connected in the end of the circuit.
C. The relation between thickness of a wire and it's current carrying capability is that, more the thickness more the current a wire can carry. So fuse wires are made of sufficient thickness. Means thinner the fuse wire, lesser is its current capacity.
D. The fuse needs to be rated slightly higher than the maximum operating current of the protected device, so that the fuse won't blow when the equipment is used.
Statement B and C are not correct about electric fuse.

When the main switch in a building is turned off or the breaker trips or the fuse burns, power to both live and neutral lines is disconnected. The earth or ground line is a safety line that must never be disconnected.

Magnets are made from magnetic metals – iron, nickel and cobalt. These are the only pure metals that can be turned into a permanent magnet. Steel is an alloy of iron and so can also be made into a magnet. Alnico and Nipermag alloys are ferromagnetic, with a high coercivity (resistance to loss of magnetism) and are used to make permanent magnets. 

1. A fuse is made of an alloy of tin and lead because it is important that the device acts without heating too much.
2. A switch in the electrical circuit is always connected to the live wire so that the socket/appliance is not live when it is switched off.
3. Alternating current is defined as the flow of charge that changes direction periodically.
4. Higher is the value of current flow, stronger is the magnetic field

So, Statement A and B are correct statement.

Magnetic Field is the region around a magnet where other magnetic material will experience a force. A magnetic field can be graphically represented by magnetic field lines which indicates its strength and direction.