Voltage & current

Question 1

electrical charge

Answer 1

an electrical property of matter that exists because of an excess or deficiency of electrons

Question 2

Coulomb’s law

Answer 2

A force (F) exists between two point-source charges (Q1, Q2) that is directly proportional to the product of the two charges and inversely proportional to the square of the distance (d) between the charges.

Question 3

coulomb

Answer 3

unit of electrical charge, symbolized by 𝑄

the total charge possessed by 6.25 x 10^18 electrons

Question 4

total charge 𝑄

Answer 4

𝑄 = (number of electrons) / (6.25 x 10^18 electrons/C)

Question 5

charge of a single electron

Answer 5

1.6 x 10^(–19) C

Question 6

positive ion

Answer 6

atom or group of atoms with a net positive charge

Question 7

valence electrons

Answer 7

electrons in the outermost shell of an atom (called the valence shell)

they have the highest energy levels and are less tightly bound to the atom than electrons that orbit closer to the nucleus

Question 8

free electron

Answer 8

an electron that absorbs a photon of sufficient energy and escapes from the atom

Question 9

negative ion

Answer 9

an atom or group of atoms with a net negative charge

Question 10

ion

Answer 10

an atom with a net electrical charge

Question 11

voltage

Answer 11

energy per unit of charge, expressed 𝑉 = 𝑊/𝑄

Question 12

unit of voltage

Answer 12

the volt (V)

one volt is the potential difference (voltage) between two points when one joule of energy is used to move one coulomb of charge from one point to the other

Question 13

electrical current (definition)

Answer 13

the rate of flow of charge, measured by the number of electrons (amount of charge) that flow past a point in a unit of time

𝐼 = 𝑄/𝑡

Question 14

definition of one ampere

Answer 14

one ampere (1 A) is the amount of current that exists when a number of electrons having a total charge of one coulomb (1 C) move through a given cross-sectional area in one second (1 s)

Question 15

resistance

Answer 15

the opposition to current, symbolized by 𝑅

Question 16

definition of one ohm

Answer 16

one ohm (1 Ω) of resistance exists when there is one ampere (1 A) of current in a material with one volt (1 V) applied across the material

Question 17

conductance

Answer 17

the reciprocal of resistance, symbolized by 𝐺

𝐺 = 1/𝑅, expressed in siemens (S)

Question 18

load

Answer 18

a device on which work is done by the current through it

Question 19

closed circuit

Answer 19

a circuit in which current has a complete path

Question 20

open circuit

Answer 20

a circuit in which the current path is broken so that there is no current

an open circuit is considered to have infinite resistance

Question 21

Ohm’s law

Answer 21

I = V/R

V = IR

R = V/I

Question 22

energy (definition)

Answer 22

the ability to do work

Question 23

power (definition)

Answer 23

the rate at which energy is used

Question 24

power (formula)

Answer 24

𝑃 = 𝑊/𝑡

Question 25

definition of one watt

Answer 25

one watt is the amount of power when one joule of energy is used in one second

Question 26

kilowatt-hour

Answer 26

1 kilowatt (1000 W) of power used for 1 hour

Question 27

Watt’s law

Answer 27

describes the amount of power dissipated in an electric circuit:

𝑃 = 𝐼²𝑅

or, using Ohm’s law:

𝑃 = 𝑉𝐼

𝑃 = 𝑉²/𝑅

Question 28

voltage drop

Answer 28

the decrease in voltage across a resistor due to a loss of energy