Unit 19 - Electricity (Ch. 78-83)

A common use for a DC generator is: A) power supply for an elevator. B) an automobile alternator. C) power supply for a machinist lathe. D) power factor correction. E) computer room power supply.

A) power supply for an elevator.

The purpose of a rectifier is to: A) increase electrical voltage. B) decrease electrical voltage. C) change AC voltage to DC voltage. D) produce a constant voltage to a pulsating voltage.

C) change AC voltage to DC voltage.

When magnetic flux lines travel and meet in opposing directions the result can be: A) generator action B) electromagnetism C) solenoid action D) motor action E) reluctance

D) motor action

A voltmeter must ___________________________________ electrical circuit. A) offer low resistance to the B) offer no resistance to the C) offer slight resistance to the D) offer high resistance to the E) interfere with the

D) offer high resistance to the

Consider a current-carrying conductor located in a magnetic field. If the current in the conductor reverses, the force tending to move the conductor will: A) increase in magnitude. B) remain constant. C) decrease in magnitude. D) reverse direction. E) be cancelled out.

D) reverse direction.

When using Fleming's left-hand rule, the following fingers represent what? 1. Thumb = ___________________________________________________. 2. Index Finger = ___________________________________________________. 3. Middle Finger = ___________________________________________________.

1. *Thumb* = Conductor motion direction, for motors. 2. *Index* = Direction of magnetic field, for motors. 3. *Middle* = Direction of current flow, for motors.

When using Fleming's right-hand rule, the following fingers represent what? 1. Thumb = ___________________________________________________. 2. Index Finger = ___________________________________________________. 3. Middle Finger = ___________________________________________________.

1. *Thumb* = Direction of motion. 2. *Index* = Direction of magnetic lines of force. 3. *Middle* = Direction of induced current flow.

List three devices that are capable of generating an electromotive force (E). 1. _______________________________________. 2. ______________________________________. 3. ______________________________________.

1. Battery 2. Mechanical driven generator 3. Photovoltaic cell ~Extras 4. Piezoelectric crystals 5. Radioisotope thermoelectric generator

Which electrical system is used with AC? *(choose all that are correct)* 1. House wiring. 2. Most power plant motors. 3. Automotive wiring. 4. Power plant battery vault.

1. House wiring. 2. Most power plant motors. 3. Automotive wiring.

List three methods that can be used to increase voltage generated as a conductor is passed through a magnetic field. 1. _______________________________________. 2. ______________________________________. 3. ______________________________________.

1. Increase the speed that the lines of force cut through a conductor (move the conductor or magnetic more quickly). 2. Increase the strength of the magnetic field. 3. Increase the number of conductors being cut by the lines of force. **Simplified: FASTER, STRONGER, MORE METAL!

Explain two reasons why a voltmeter must have a very high resistance.

1. Only a very small current, sufficient to cause full-scale movement of the moving coil and pointer, is permitted when full-scale voltage is applied. 2. The voltmeter must not cause a current drain which would reduce the voltage being measured on a voltage source, or around an electrical load.

Three variables that determine the strength of a magnetic field around an electro-magnet are: 1. _______________________________________. 2. ______________________________________. 3. ______________________________________.

1. The current (amps) flowing through the conductor. 2. The number of turns of wire in the coil. 3. The permeability of the core.

Which electrical system is used with DC? *(choose all that are correct)* 1. House wiring. 2. Most power plant motors. 3. Automotive wiring. 4. Power plant battery vault.

4. Power plant battery vault.

When using an electrical meter to check that a circuit is safe to work on, it is important to verify the proper scale, current, or both that is being used because? A) it may appear that no voltage or current is present and therefore safe. B) the meter will be damaged. C) the user will be subjecting himself or herself to danger. D) the main high voltage transformer circuit will be opened. E) electrical wiring will be damaged by fire or overheating.

A) it may appear that no voltage or current is present and therefore safe.

The instrument used to measure electrical power used in a period of time, is the: A) kilowatt hour meter B) voltmeter C) ohmmeter D) milli-ammeter E) oscilloscope

A) kilowatt hour meter

An Ammeter must _________________________ to the electrical circuit. A) offer low resistance B) offer no resistance C) offer a slight resistance D) offer a high resistance E) apply a voltage

A) offer low resistance

If a material has a low reluctance, it has a high __________________. A) permeability. B) conductivity. C) fluctuation. D) magnetism. E) capacitance.

A) permeability.

If an electrical ______________ is placed across a conductor, the electrons will drift from the negative end towards the positive end of the conductor. A) potential B) current C) resistance D) wire E) meter

A) potential

Current flow is: A) proportional to the applied voltage. B) proportional to the resistance. C) reversed by a resistance. D) increased by a decrease in applied voltage. E) inversely proportional to the applied voltage.

A) proportional to the applied voltage.

A power meter/kilowatt hour meter: A) reads the actual power consumed. B) does not require a multiplying factor. C) reads only a small percentage of the actual load. D) will calculate the actual cost of the power. E) does not take into account the system voltage.

A) reads the actual power consumed. ?????????

When AC action causes a counter current in a coil, it is termed: A) self inductance. B) capacitance. C) hysteresis. D) current generation. E) electromagnetic induction.

A) self inductance.

A conductor supplied with current while in a magnetic field will: A) tend to move at right angles to the flux lines. B) tend to remain stationary. C) want to move with the flux lines. D) have a current induced into it. E) demonstrate generator theory.

A) tend to move at right angles to the flux lines.

Clamp-on ammeter readings may be inaccurate if: A) jaws are dirty or misaligned. B) circuit voltage is too high. C) circuit resistance is too low. D) circuit power is too high. E) conductor insulation is too thick.

A) the jaws are dirty or misaligned.

Describe the operation of a clamp-on type ammeter.

Alternating current flow passing through a conductor produced a magnetic flux around the conductor. When the laws of the clamp-on meter encircle the conductor, the magnetic flux passes through the jaws, linking the primary to the secondary of the "transformer". The alternating magnetic flux cutting the secondary coil induces an electromotive force in the secondary coil, producing current flow through the meter circuit. The magnitude of the current produced in the secondary coil is directly proportional to the current flowing through the conductor.

Name the two basic types of electrical test meters.

Analog meters and Digital meters

Low voltage systems may have an acceptable voltage variation of plus or minus __________. A) 10% B) 5% C) 1.5% D) 7.5% E) 12.5%

B) 5%

The major difference between an AC and a DC generator is that a DC generator has __________________. A) a rotor B) a commutator C) slip rings D) a field E) a stator

B) a commutator

The right-hand rule is used to: A) indicate the speed of a motor. B) determine the direction of induced current flow. C) determine the frequency of an alternator. D) determine the direction of motor rotation. E) determine the magnetic flux rotation.

B) determine the direction of induced current flow.

The flow of electrons in a uniform direction is called: A) voltage drop B) electrical current flow C) potential difference D) electromotive force E) direct current

B) electrical current flow

Ammeters are connected: A) in parallel with the circuit. B) in series with the circuit. C) in parallel with the circuit to measure the resistance. D) so that voltage will bypass the meter. E) to the negative and positive terminals of the battery.

B) in series with the circuit.

Magnetic flux can be said to be: A) lines of force within a magnet and flowing N to S. B) lines of force outside a magnet and flowing N to S. C) a magnetic field. D) lines of force flowing S to N outside a magnet. E) lines of force flowing in a magnet.

B) lines of force outside a magnet and flowing N to S.

Under normal circumstances, the heat produced by the electrical wires of a circuit is very small due to the: A) large diameter of the conductor. B) low resistance of the conductor. C) long length of the conductor. D) insulation wrapped around. E) small diameter of the conductor.

B) low resistance of the conductor.

In a solenoid valve, the valve is open when: A) current flow has stopped. B) magnetic flux is increased.

B) magnetic flux is increased.

The best type of diagram for showing supply and distribution systems is the: A) riser. B) one-line. C) elementary. D) connection. E) terminal and connection.

B) one-line.

If a material provides resistance to magnetic flux, it is demonstrating ______________________. A) resistance B) reluctance C) impedance D) repulsion E) voltage drop

B) reluctance

Faraday discovered: A) the right-hand rule for conductors. B) that a conductor will have a voltage induced if it cuts magnetic flux. C) the left-hand rule for motors. D) the left-hand rule for generators. E) that current flows from positive to negative.

B) that a conductor will have a voltage induced if it cuts magnetic flux.

Equivalent resistance is decreased: A) when voltage is decreased. B) when a circuit is in parallel. C) if the amperage is increased. D) when a circuit is in series. E) when a circuit is opened.

B) when a circuit is in parallel.

In a single phase 240 volt circuit, three are three wires to connect motors and other devices. State the colours of these wires and what each connect is called.

Black - live circuit conductor. White - grounded circuit conductor or neutral. Red - live circuit conductor.

When working will high voltage systems, the minimum distance of approach should be ____________________. A) 1 metre B) 4 metres C) 2 metres D) 3 metres.. E) 60 centimetres..

C) 2 metres

The maximum voltage generated by a single loop DC generator occurs, when the conductor is cutting the magnetic lines of force at an angle of _________. A) 0° B) 45° C) 90° D) 120° E) 180°

C) 90°

A clamp-on ammeter measures current flow by using: A) shunting current through a milli-ammeter B) differential current flow between two conductors C) a basic transformer principle D) a portion of circuit resistance E) electromagnetism

C) a basic transformer principle.

The EMF (electromotive force) of an electrical circuit may be provided by: A) the load B) the circuit resistance C) a battery D) the current E) the conductors

C) a battery

In an atom the electrons: A) are located with the nucleus. B) are repelled by the neutrons. C) are attracted to the protons. D) are large in size when compared to protons. E) orbit only the neutrons.

C) are attracted to the protons.

An electrical distribution system is composed of service, feeders and: A) secondary circuits. B) primary circuits. C) branch circuits. D) trunk circuits. E) tertiary circuits.

C) branch circuits.

The total number of lines of force in a magnetic field is: A) known as the EMF. B) controlled by varying the temperature. C) called the magnetic flux. D) determined by the north magnetic pole. E) depends on the force of gravity.

C) called the magnetic flux.

A typical extra low voltage device would be a: A) toaster. B) set of tree lights. C) door bell. D) dry cell battery charger. E) night light.

C) door bell.

Some of the fire hazards of transformer cooling can be compensated for by using: A) chelates. B) anti-foaming substances. C) florinated hydrocarbons. D) freons. E) organic compounds.

C) florinated hydrocarbons.

If a conductor is held stationary and a magnetic field is moved across it, it behaves according to: A) motor action. B) electromagnetism. C) generator action. D) transformer action. E) conduction.

C) generator action.

A kilowatt-hour meter has a small motor which: A) turns at a constant speed. B) slows down as power consumption increases. C) has a speed proportional to power consumption. D) indicates the multiplier to be used when reading the meter. E) moves the meter demand pointer.

C) has a speed proportional to power consumption.

A conductor's resistance is: A) directly proportional to its cross-sectional area. B) directly proportional to its diameter. C) inversely proportional to its cross-sectional area. D) not affected by the cross-sectional area. E) measured in micro-Newtons.

C) inversely proportional to its cross-sectional area.

In a series wound DC generator: A) brushes change DC to AC for the armature. B) the shunt winding is connected taps in before the series winding. C) load current passes through the field windings. D) the shunt winding is connected after the series winding. E) there are no field poles.

C) load current passes through the field windings.

Magnetite is also known as __________________. A) iron ore B) non-ferrous metal C) lodestone D) hematite E) ferrite

C) lodestone

Ammeters are connected with the negative or black lead connected to the: A) positive side of the circuit. B) north pole of the circuit. C) negative side of the circuit. D) switch of the circuit. E) neutral wire of the circuit.

C) negative side of the circuit.

Current flow is inversely proportional to the __________________. A) voltage. B) amperage. C) resistance. D) wattage. E) conductance.

C) resistance.

The major difference between an AC and a DC generator is that a AC generator has ______________________. A) a rotor B) a commutator C) slip rings D) a field E) a stator

C) slip rings

When reading the dials of a power meter, read: A) them in the sequence shown by the letters under each. B) them from left to right. C) the ones that rotate clockwise first. D) them from right to left. E) them only at the request of the utility company.

D) them from right to left.

A rheostat is used to ______________________ the field strength in a DC machine. A) stop B) make C) heat D) vary E) remover

D) vary

The most common measurement made with an electrical meter is __________________. A) amperage B) watts C) resistance D) voltage E) capacitance

D) voltage

Higher voltages are stepped down to a maximum of ______________ before the kWh meter can be used to measure the amount. A) 600 volts B) 220 volts C) 240 volts D) 110 volts E) 120 volts

E) 120 volts * If an operation requires 600 volt service the power is stepped down to 120 volts to accommodate the meter.

The purpose of having an upward movement of a switch handle to close the switch is: A) To have the handle out of the way. B) To meet the requirements of the electrical codes. C) Because it is easier to operate when opening the switch. D) It indicates the condition of the circuit. E) To prevent the switch from closing due to gravity.

E) To prevent the switch from closing due to gravity.

The strength of the magnetic flux about an electromagnet is: A) proportional to the current flowing through the coil. B) proportional to the number of turns in the coil. C) proportional to the permeability of the core. D) A and B. E) all of the above.

E) all of the above. A) proportional to the current flowing through the coil. B) proportional to the number of turns in the coil. C) proportional to the permeability of the core.

Alternators must run at constant speed in order to maintain: A) current. B) power. C) voltage. D) resistance. E) frequency.

E) frequency.

The space or zone around a magnet through which lines of force travel is termed: A) magnetic flux. B) permeability. C) reluctance. D) magnetic strength. E) magentic field.

E) magentic field.

A current carrying conductor being moved by a magnetic field illustrates the principle known as: A) magnetic flux. B) electrolysis. C) hydro-electrics. D) generator action. E) motor action.

E) motor action.

The black demand pointer of a power meter: A) moves the red pointer. B) reads the current demand. C) resets automatically. D) indicates the maximum voltage being drawn. E) must be manually reset.

E) must be manually reset.

Utility companies have a surcharge to their customers based on: A) the maximum voltage used. B) the maximum amperage used. C) system capacitance. D) transformer efficiency. E) peak power demand.

E) peak power demand.

The property that determines whether a material will be easily magnetized or not is called ____________________. A) reaction. B) conductivity. C) fluctuation. D) magnetism. E) permeability.

E) permeability.

Atoms that have greater than 3 electrons in the outer shell are: A) positively charged B) good conductors C) poor insulators D) neutrally charged E) poor conductors

E) poor conductors

The output voltage of a particular DC generator rises sharply from minimum load to full load. This generator is a ___________ generator. A) shunt B) compound C) synchronous D) wound-rotor E) series

E) series

AC electrical supplies and systems may be divided into voltage classes. List the three classes and state the voltage range of each.

Extra Low Voltage - below 50 volts Low Voltage - between 50 and 600 volts High Voltage - above 600 volts

Describe the operation of a single-phase transformer that has a primary and secondary winding with AC current passing through the primary winding.

Since AC is applied to the primary windings , the current flow increases and decreases at 60 cycles per second which results in a magnetic field building up and collapsing around the coil at the same speed. As lines of magnetic flux build up and collapse, they pass through the windings of the secondary coil. This passing generates a voltage in the secondary windings the same frequency as that applied to the primary.

Transformers are rated in terms of what two units?

VA kVA

The most common measurements made with a handheld meter are ________________ , ________________and ________________.

Voltage, Current (amps) & Resistance (ohms)

Describe the relationship between an electric current flowing through a conductor and the magnetic field around a conductor.

Whenever an electric current is passed through a conductor, a circular magnetic field is produced around the conductor; the direction of the magnetic field is dependent on the direction of the electrical current flow.

Iron and steel may be magnetized by rubbing the metal with a _________________.

a magnet using one of the polarities only.

Power is transferred to or from the rotor or armature commutator of a DC machine through carbon ___________________ mounted in insulated ____________________ loaded holders.

carbon brushes, spring loaded holders

____________________ current flow is from positive to negative. A) Alternating B) Direct C) Static D) Conventional E) Electron

d) Conventional

The electrons of an atom are located in ___________________ that surrounds the ______________________ of an atom.

electron cloud/shells, the nucleus

In order to provide the strength of magnetic field required in large DC machines, stationary electromagnets called ___________________ are used.

field poles

Conventional flow notation depicts the flow of electrons from ____________________ to ____________________ and follows the ____________________ rule. Whoever the electron flow notation depicts the electrons flowing the correct way through the wire and follows the ____________________ rule. The electron flow notation is critical for understanding how ___________________________ like LEDs work.

positive to negative right-hand rule left-hand rule semi-conductors

A basic law of electricity is: unlike charges attract each other and like charges __________________________.

repel each other

A manual device that can be placed in series with the field of a DC generator to control output voltage by regulating current flow through the field is a ____________________.

rheostat

Explain the difference between a simple pole switch and a two pole switch.

A single pole switch opens only one side, or one lead, in an electrical circuit; whereas, a two pole switch opens both sides or leads or two separate leads simultaniously.

High amperage is stepped down to a maximum of _____ A before the kWh meter can be used to measure the amount. A) 5 B) 32 C) 100 D) 110 E) 120

A) 5 amperes * This 5 amps represents a larger actual amperage usage by the home or operation. This is through the usage of multipliers.

Increasing load on a motor or other electrical device is indicated by? A) Increased current flow. B) Increased voltage. C) Increased resistance. D) All of the above.

A) Increased current flow.

The galvanometer is? A) a sensitive current measuring device. B) a sensitive voltage measuring device. C) a sensitive resistance measuring device. D) all of the above.

A) a sensitive current measuring device.

Current flow direction and intensity will: A) affect magnetic field direction and intensity. B) affect the voltage. C) affect the resistance of a circuit. D) not affect electromagnetic field direction. E) not affect electromagnetic field intensity.

A) affect magnetic field direction and intensity.

When a number of electrons pass a given point over a specific time period the energy may be referred to as: A) an ampere B) voltage C) an ohm D) power or watts E) electromotive force

A) an ampere

A conductor's resistance is: A) directly proportional to its length. B) directly proportional to its diameter. C) inversely proportional to its length. D) not affected by the cross-sectional area. E) measured in micro-Newtons.

A) directly proportional to its length.

Most conductors tend to: A) increase in resistance with increase in temperature. B) decrease in resistance with increase in temperature. C) shrink when heated. D) melt when voltage is applied. E) oscillate when voltage is applied.

A) increase in resistance with increase in temperature.

The load current has no effect on the field excitation of a: A) compound wound generator B) series wound generator C) shunt wound generator D) separately excited generator. E) short-shunt generator

D) separately excited generator.

In an equivalent circuit developed from a multi-resistor series circuit: A) the resistance will be the reciprocal sum of the original resistances. B) voltage drop will be the same as for each of the original resistances. C) the sum of voltage drops across the original resistances will be equal to the voltage drop of the equivalent circuit. D) original circuit resistances will each have to be the same as the equivalent resistance. E) amperage flowing will be different than the original circuit amperage flowing through each resistance.

C) the sum of voltage drops across the original resistances will be equal to the voltage drop of the equivalent circuit.

When current flows in a conductor: A) AC voltage is generated. B) the voltage is reduced in the conductor. C) the conductor develops north and south poles. D) a circular magnetic field is set up around the conductor. E) all magnetic forces are dissipated.

D) a circular magnetic field is set up around the conductor.

An open circuit is one which: A) a switch is closed. B) the current flows through the resistance. C) the wires are bare. D) a switch is open. E) voltage may exit.

D) a switch is open.

The yoke that supports the main components of the DC machine is frequently made of: A) copper or brass. B) mica and carbon. C) copper and carbon. D) cast steel or iron. E) aluminum.

D) cast steel or iron.

When using Fleming's left-hand rule, the index finger represents: A) magnetic flux direction, for generators. B) conductor motion direction, for motors. C) conductor motion direction, for generators. D) flux direction, for motors. E) direction of current flow, for motors.

D) flux direction, for motors.

An active/operating current transformer should never: A) be inspected until properly grounded. B) have its primary circuit opened. C) produce excessively high voltages. D) have its secondary circuit opened first. E) have its secondary connected to a meter.

D) have its secondary circuit opened first.

A voltmeter is connected to a circuit. A) in series. B) in series and parallel. C) in either series or parallel. D) in parallel. E) between the last resistor and the source.

D) in parallel.

Describe the steps that must be taken to ensure that high voltage circuits are safe to work on.

The disconnect switches must be locked in the OPEN position. (open means the electrical path is broken/disconnected) Ground connections must be attached to ensure that the circuits are fully de-energized.

State the purpose of a multiplier as used on a demand meter.

The multiplier is used to allow a meter that measures lower power demand to be used to indicate higher power consumption. The actual power consumption is determined by multiplying the meter reading by the multipliers.