MCQs electricity and magnetism

Wire wound resistor

Carbon Resistor

Ceramic resistor

Precision resistor

25 W

Power rating of wire-wound resistor

Metal Film Resistor

Open resistor resistance when measured by ohmmeter

infinite

Chip resistor

Temperature where solder melts

360 deg F

Wattage of antenna wire outdoors

250W

Wattage of PC board

25-35W

Wattage of indoor electrical wiring

50-100W

Wave

Method of soldering which can make hundreds of soldered connections at once on PC boards

take the power times 2

how to compute for power rating of a resistor

Domain

Group of magnetically aligned atom

Magnet

An atom forms this when a great amount of electrons rotate around a nucleus on the same direction

North pole of coil

When the fingers of the left hand are around a coil in the direction of current flow, to what doe the thumb point?

horizontal at the geomagnetic equator

Geomagnetic lines of flux are

Electromagnet/solenoid

A magnet that requires current in a coil to create a magnetic field line

Contract into wires

When current ceases in a coil, what happens to the magnetic field lines

Torpid

• electromagnet

• No magnetic poles

• Doughnut like

• Core used is iron around which the coil is wound

Attract each other

If 2 parallel wires have similar direction flowing, what effect will be produced?

Hall effect

Small voltage is generated across the width of a current carrying conductor in an external magnetic field this effect is called?

Miller effect

This is the effect where in the capacitance in an electronic circuit is amplified due to the gain of the amplifier so the capacitance affects the response of the circuit or the amplifier as it can change the frequency

+- 200,000

This is the permeability of pure iron

coercivity

It is the quantity of magnetizing force needed to counter balance, the residual magnetism of a magnetic material. It is the magnetic field strength that describes a measure of a materials resistance to demagnetization.

Into the field, which surrounds each atom

Where do magnetic lines go when they collapse back into a wire?

Permanent magnet

This is a magnet which retains its magnetic properties in the absence of Korean or inducing field

As strong the magnetizing field, physical shock, high temperature temperatures

a Commercial permanent magnet will last indefinitely if it is not subjected to

Iron magnetic

What does ferromagnetic mean

Domain

Into what basic entities do molecules of ferromagnetic substances form

Domain

Into what basic entities do molecules of ferromagnetic substances form

Diamagnetic

In what category is a substance that tries to turn at right angles to a magnetic field this is also a property where in it is weakly repel by a magnetic field

Paramagnetic

In what category is a substance that tries to line up in the direction of a magnetic field

Residual magnetism

It is the flux density which exists in the iron core when the magnetic field intensity is reduced to zero

retentivity

It is the ability of ferromagnetic material to retain a significant portion of its magnetism after the external force has been removed

Paramagnetic and diamagnetic

These substances Have no retentivity and hysteresis loop

hysteresis

It is the lag of magnetic flux density behind the magnetizing field strength

Hysteresis loop

This is the closest curve that shows the flux density and magnetic field strength

Very narrow

What shape does the hysteresis loop must have to have the material be a good relay core

Very wide

This is the shape of the history is for a permanent magnet

Magnetic flux lines within itself

A ferromagnetic material concentrates?

Curie point

The point at which a magnetic material loses its ferromagnetic properties

Magnetic flux density of the core divided by the magnetic flux in the air

This is how to solve the relative permeability

Demagnetizes

What happens to a permanent magnet in the core of a coil carrying a heavy alternating current?

Due to hysteresis loss

Why my up permanent magnet in the core of a coil carrying a heavy current heat up?

Capture

What does magnetic shield do to lines of force?

10^8

How many lines of force must be cut per second to produce an average of one volt

Magnetostriction

This is the effect whereby a ferromagnetic, material changes size or shape when magnetized or demagnetized

Silver

This is the material used for really contacts which can be easily cleaned

Tungsten

This is a durable material used for relay contacts

If the fingers of the left hand and circle the coil in the same direction as electron flow, the thumb points in the direction of the north Pole

The left-hand rule for solenoids states that

A stronger field towards a weaker field

Motor action always tends to produce motion from

A stronger field towards a weaker field

Motor action always tends to produce motion from

Relative motion between the wire and magnetic field

A conductor will have an induced current or voltage only when there is

The minimum relay coil current required to energize a relay

For a relay, the pickup current is defined as

Armature

The movable arm of a attraction type is called the

The rate at which the conduct bar cuts the magnetic flux and the number of magnetic flux lines which are caught by the conductor

For a conductor being moved through a magnetic field the amount of induced voltage is determined by

Alternating current

degaussing(process of reducing residual magnetic field) is done with

Increase with higher frequencies

Hysteresis losses

All of the molecular dips and magnetic domains are aligned by the magnetic force, and the flux density cannot be increased in the core when the field intensity is increased

Saturation of an iron core occurs when

At right angles to the direction of current

For a single conductor, carrying an alternating current, the associated magnetic field is

The minimum amount of free lake coil current required to keep a relay energized

For a relay the holding current is defined as