ITEC 220 Test #2 Flashcards by Pat Knott

Series circuit

Circuit in which current flows in one direction

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Parallel circuit

Circuit in which current flows in one direction then alternates back and forth

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Combination circuit

A circuit with both series and parallel sections

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Series-parallel/complex circuit

Circuits with any combination of series and parallel sections

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How many paths are in a series circuit

1 path

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What is the disadvantage of connecting a large number of bulbs in series

A voltage drop

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Are lights in our homes connected in series

No in parallel

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How many paths are there in a parallel circuit

2 or more paths

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What is the smallest number of paths a parallel circuit can have

2 paths

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D’Arsonval meter movement

A meter movement that uses stationary magnet structure and a moving coil

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Moving-coil meter

A meter movement that uses stationary magnet structure and a moving coil

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Rectifier

A device that allows current to go one direction easily, but not the other direction

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Full-scale value

The current that represents the maximum deflection of the pointer on the scale

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Current sensitivity

The method of stating the resistance need to limit current to the full-scale value

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Ohms per volt

The unit stating sensitivity of a meter movement

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Shunt resistor

A resistor in parallel to the meter movement that measures the current greater than the full-scale value

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Multiplier resistor

A resistor in series to the meter movement that measures the voltage greater that the full-scale value

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Kirchhoff’s Voltage Law

In a circuit, the algebraic sum of the voltage drop is equal to the algebraic sum of the voltage rises across the source

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Kirchhoff’s current law

The sum of the currents entering the junction are equal to the sum of the currents leaving the junction

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What is the maximum voltage that can be measured when using 100 volt setting

100 V

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When using the 1,000 volt range, by what number must the scale reading be multiplied

100

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Axial resistor

A cylindrical shaped resistor whose leads come out of its axis

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Radial resistor

A cylindrical shaped resistor whose leads come out at the sides or at the radius of the cylinder

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What is the purpose of the function selector switch on a multimeter

To select different voltages and currents

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An ohmmeter measures resistance through a conductor and resistor through a

Series circuit

What would be the resistance of a section of insulating material

Infinite

What is indicated by the first and second color bands on a resistor

The first and second digits of the resistors value

What is indicated by the third and fourth color bands on a resistor

The third is the multiplier and the fourth is the resistors tolerance

Gold fourth band

Plus/minus 5%

Silver fourth band

Plus/minus 10%

No fourth band

Plus/minus 20%

Variable resistor

A resistor whose resistance can be changed without disconnecting the circuit

Rheostat

A variable resistor, which has two terminals, and is used to control the current in a circuit

Potentiometer

A variable resistor, which has three terminals, and is used as a adjustable voltage divider

What is rheostat used for

To control the current in a circuit

What is a potentiometer used for

as a adjustable voltage divider

What is the physical difference between a rheostat and a potentiometer

A rheostat has two terminals and a potentiometer has three terminals

To control the current through a lamp, is the rheostat connected in parallel or in series

Connected in series

Define Kinetic energy

Energy associated with motion

Define Power

The rate of expending energy (doing work)

Basic unit of power

Watt

Define watt

One watt is the amount of work done in one second by one volt in moving one coulomb of charge

One Joule of energy is referred to as

A watt-second

1 watt hour equals

3,600 joules

Define horsepower

The mechanical unit of power

The cold resistance of a light bulb is less than its hot resistance. Would it be more likely to burn out when first turned on or later

First turned on

Residual magnetism

Magnetism that a material retains after the magnetizing force has been removed

Poles

The ends of a magnet (labeled north and south)

Magnetic field

Any region in which a magnetic force is exerted

Ferromagnetic

Any material that exhibits strong magnetic properties

Magnetism by induction

The magnetism a object acquires by being in a magnetic field

Permanent/hard magnets

Material that retains much of the magnetism after the magnetic force has been removed

temporary/soft magnets

Material that loses its magnetism after the magnetic force has been removed

Permeability

Measure of the ability of a substance to conduct magnetic flux

Reluctance

Ability of a material to oppose passage of magnetic lines of force through them

Magnetic dipoles

Smallest particles of a substance that has magnetic properties

1 kilowatt is...

1,000 watts

To convert watts to kilowatts

Move the decimal three places to the left

1 kilowatt-hour is.....

1,000 watt-hours

To convert watt-hours to kilowatt-hours

Move the decimal three places to the left

A watt is equivalent to

1 joule per second

A unit of power (horsepower) is equivalent to

550 foot-pounds of work done in one second

One watt is the same as an electromotive force of....

One volt multiplied by a current of one ampere

Unlike poles of magnets attract or do not attract

Attract

Is the pointer on the compass needle a north magnetic pole or a south magnetic pole

South magnetic pole

Standing halfway between the equator and the south geographic pole of the earth, in which direction would the compass point

North

All materials are affected when placed close to magnets

False

The north pole of a magnet induces what pole into the end of a material attached to it

South

How would you demagnetize a screw driver

Heat it up, hit it with a hammer, or put it in another magnetic field with AC current

Two ferromagnetic substances

Nickle and Cobalt

Two non-ferromagnetic substances

Chrome and Zinc

Electromagnetism

The phenomenon whereby an electrical current produces magnetic effects

Coil / Solenoid

An electrical device that consists of turning insulated wires that produce a magnetic field

Is a magnetic field around a wire temporary of permanent

Temporary

The intensity of a magnetic field is (directly, inversely) proportional to the distance from a conductor

Inversely

Winding more turns on a coil will (increase, decrease) the magnetic field

Increase

Electromagnet

Is a device that behaves as a magnet when external power is applied to it.

What is an example of a electromagnet

A solenoid with a soft iron-core

Relay

A device that is operated by changing conditions of one electric circuit to affect the operation of devices in the same circuit or different ones

Why is an electromagnet preferred over a permanent magnet

It can be turned off and used in mechanical apps

Electromagnets are why type of magnets

Temporary magnets

What must you have to operate an electromagnet

External power and a solenoid with soft iron-core

What is another name for a electromechanical switch

Relay

Induced voltage / Induced current

Voltage produced in a conductor by its movement in a magnetic field

In what direction must a conductor be moved to induce maximum current into the conductor

Perpendicular

What can be done to a conductor to increase the current induced into it when it is moved through a magnetic field

Move the conductor at right angles

What effect does the use of a steel core have with respect to induced current

The steel core only picks up part of the magnetic field

When current in a coil is neither increasing or decreasing, what is the state of the field surrounding the coil

Remains in a steady state

Why does a current-carrying wire move when in a magnetic field

Because there is a magnetic field around the wire

Name some uses of current-carrying conductors moving in a magnetic field

Motors, generators, and transformers

Left hand rule

Determines the direction of the induced current in the conductor

What do the fingers represent in the left hand rule

Thumb - motion of conductor, Index finger - location of magnetic field, and middle finger - direction of the current flow

Right hand rule

Determines the motion of the current-carrying conductor in a magnetic field

What do the fingers represent in the right hand rule

Thumb - motion of the conductor, Index finger - the direction of the magnetic field, and middle finger - the direction of current flow

How can an electric bell be made into a buzzer

Remove the hammer and bell

Uses of a buzzer

Attention-getting device and doorbell replacement

What is meant by normally opend contacts on a relay

Normally open contacts are when the relay coils are deenergized. They close when the relay coil is energized

What is the purpose of a circuit breaker

It protects a circuit from an excessive-current condition