Unit 19 Electricity

Question 1

In an atom the electrons

Answer 1

are attracted to the protons

Question 2

An open circuit is one in which

Answer 2

a switch is open

Question 3

Ohms law can be stated as

Answer 3

E=IR

Question 4

3 devices that are capable of generating an electromotive force

Answer 4

photocells
chemical reaction (battery)
mechanically driven generator

Question 5

The electrical pressure that causes electrons to flow through a circuit

Answer 5

Electromotive force

Question 6

A unit of electrical resistance

Answer 6

Ohm

Question 7

A unit of electrical power

Answer 7

Watt

Question 8

A mechanical device used to open and close an electrical circuit

Answer 8

a switch

Question 9

A unit of electrical current flow

Answer 9

Ampere

Question 10

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

Answer 10

Fuse

Question 11

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

Answer 11

Potential Difference

Question 12

A unit of electrical pressure

Answer 12

Voltage

Question 13

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

Answer 13

Determine:

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

Question 14

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

Answer 14

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

Question 15

The relationship between diameter and resistance

Answer 15

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

Question 16

the unit of work

Answer 16

joule

Question 17

formula for electrical power

Answer 17

P= IE

Question 18

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

Answer 18

flux or flux density

Question 19

two metals that do not have magnetic properties

Answer 19

silver and copper

Question 20

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

Answer 20

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

Question 21

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

Answer 21

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.

Question 22

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

Answer 22

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

Question 23

The sum of the magnetic lines of force about a magnet

Answer 23

Magnetic flux

Question 24

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

Answer 24

Magnetic field

Question 25

What is the phenomenon discovered by Michael Faraday

Answer 25

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

Question 26

Describe the right hand rule for generators

Answer 26

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.

Question 27

The purpose of a rectifier is to

Answer 27

Change AC voltage to DC

Question 28

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

Answer 28

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

Question 29

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

Answer 29

Direct Current

Question 30

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

Answer 30

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.

Question 31

what is the left hand rule for motors

Answer 31

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