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Power Engineering > Unit 19 Electricity > Flashcards

Unit 19 Electricity Flashcards

1
Q

In an atom the electrons

A

are attracted to the protons

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2
Q

An open circuit is one in which

A

a switch is open

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3
Q

Ohms law can be stated as

A

E=IR

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4
Q

3 devices that are capable of generating an electromotive force

A 
photocells
chemical reaction (battery)
mechanically driven generator
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5
Q

The electrical pressure that causes electrons to flow through a circuit

A

Electromotive force

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6
Q

A unit of electrical resistance

A

Ohm

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7
Q

A unit of electrical power

A

Watt

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8
Q

A mechanical device used to open and close an electrical circuit

A

a switch

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9
Q

A unit of electrical current flow

A

Ampere

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10
Q

A device that is place in an electric circuit which melts to protect the circuit form overloading

A

Fuse

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11
Q

The difference in voltage between one end of a wire and the other ( or between any two points)

A

Potential Difference

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12
Q

A unit of electrical pressure

A

Voltage

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13
Q

Three resistors of 50, 40 and 20 ohms respectively are connected in parallel to an electrical supply. If the current flowing through the 20 ohm resistor is 5 amperes

A

Determine:

a. the supply voltage
b. the current flowing through the 50 and 40 ohm
c. the total line current

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14
Q

The relationship between the resistance and a change in length of the conductor

A

The resistance varies directly with the change of length. (if the length is doubled the resistance is doubled)

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15
Q

The relationship between diameter and resistance

A

if the diameter is doubled, the resistance is reduced 4 times

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16
Q

the unit of work

A

joule

17
Q

formula for electrical power

A

P= IE

18
Q

The total number of lines of force in a magnetic field determine the value of the

A

flux or flux density

19
Q

two metals that do not have magnetic properties

A

silver and copper

20
Q

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

A

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

21
Q

Name and describe the rule used to determine the direction of a magnetic field around a single conductor

A

The right hand rule is used to mentally grasp the conductor with the thumb pointing in the direction of the current flow. the fingers then point in the direction of the magnetic field.

22
Q

How is the magnetic field affected when a current carrying conductor is wrapped into a coil

A

The magnetic field is reinforced and increased by each wrap of the wire in the coil

23
Q

The sum of the magnetic lines of force about a magnet

A

Magnetic flux

24
Q

The space around a magnet through which the magnetic lines of flux are considered to travel

A

Magnetic field

25
Q

What is the phenomenon discovered by Michael Faraday

A

When a conductor is moved across a magnetic field, an electric current is induced in the conductor

26
Q

Describe the right hand rule for generators

A

thumb and first 2 fingers of the right hand. Thumb points in the direction of motion, the index points in the direction of the magnetic lines of force, second finger indicates the direction of induced current flow.

27
Q

The purpose of a rectifier is to

A

Change AC voltage to DC

28
Q

3 methods to increase the voltage generated as a conductor is passed through a magnetic field

A

Increase the speed the lines of force are cut
Increase the strength of the magnetic field
Increase the number of conductors

29
Q

When a generator is used to produce electric current and the generator uses a commutator, the voltage will be

A

Direct Current

30
Q

State the basic principle of motor action that occurs with a current carrying conductor when placed in a magnetic field

A

When conductor carrying a current is placed in an magnetic field, the conductor tends to move in a direction at right angles to the field.

31
Q

what is the left hand rule for motors

A

determines the direction of the force exerted on an current carrying conductor placed in a magnetic field. Thumb, index, and middle finger held at 90degrees to each plane. The index finger represents the direction of the magnetic flux, second finger represent the direction of current flow, and the thumb indicates the direction of the force acting on the conductor

Power Engineering (7 decks)

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