electric

Question 1

current

Answer 1

rate of flow of charge

Question 2

e

Answer 2

elementary charge

Question 3

examples of charge carriers

Answer 3

electrons - in metals
ions in electrolytes

Question 4

conventional current

Answer 4

flow of positive charge, flows from positive to negative

Question 5

electron flow

Answer 5

current flows from negative to positive

Question 5

kirchoffs fist law

Answer 5

sum of current entering a junction is the same as the sum of the current leaving a junction

charge is conserved

Question 6

mean drift velocity

Answer 6

average velocity of the charge carriers due to the applied electric field, it has to be an average because they are often moving randomly in all directions

Question 7

put conductors, semi conductors and insulators in order from highest n to lowest

Answer 7

highest = conductors
semiconductors
lowest = insulators

Question 8

potential difference

Answer 8

work done per unit charge, the difference in potential between to points in a circuit

Question 9

what is the difference between voltage and emf

Answer 9

voltage is the energy transferred per coulomb across a load resistance

emf is the total amount of work done by the battery per coulomb

Question 10

true or false: the kinetic energy of an electron is multiplied by its charge multiplied by the voltage

Answer 10

true, eV = 1/2 mv^2

Question 11

resistance

Answer 11

the potential difference required for each unit of current that flows through a resistor / how difficult it is for current to flow through an appliance

R = V/I

Question 12

1 ohm

Answer 12

when a resistor is subject to a voltage of 1V and allows a current of 1A through, its resistance is 1 ohm

Question 13

ohmic conductor

Answer 13

conductor that obeys ohms law

Question 14

ohms law

Answer 14

the current through an ohmic conductor is directly proportional to the potential difference across it, this is only true if the temperature is constant

Question 15

gradient of potential diff graph

Answer 15

1/R as gradient = rise in current/charge in potential difference

Question 16

what does an s shaped graph represent

Answer 16

a filament lamp
as current increases resistance increases

Question 17

why does the current increasing on a filament lamp cause an increase in resistance

Answer 17

• flow of current causes collisions between electrons and the metal lattice
• these collisions increase the temp of lattice
• as temp increases more collisions occur causing the resistance to increase

Question 18

diode

Answer 18

appliance that only allows current to flow in one direction

graph is flat then curves upwards

Question 19

LDR

Answer 19

a semiconductor that is sensitive to light: as the light intensity increases the resistance decreases

Question 20

how does a thermistor work

Answer 20

similar to LDR but as the temp increases the resistance decreases, negative temp coefficient

Question 21

resistivity

Answer 21

property of a metal which shows how easy or difficult it is is for current to flow in the metal

P= RA/L

Question 22

experiment to determine resistivity

Answer 22

• measure diameter of wire
• use diameter to calc CSA
• set up circuit
• vary length and record voltage and current
• use R = V/I to work out resistance
• plot graph of resistance against length
• grad = resistivity / area

Question 23

true/false: the resistivity of both metals and semiconductors increases with temp

Answer 23

false:

• the resistivity of a metal increases with temp because as the metal ions heat up they vibrate more and the electrons bang into them and slow down
• some semi conductors get less resistive as temp increases, because supplying energy actually causes more charge carriers to be released so current can flow more easily

Question 24

power

Answer 24

rate of energy transfer

Question 25

why do electricity companies use KWH rather than joules or watts

Answer 25

impractical

Question 26

kirchoffs second law

Answer 26

for any path of a circuit the sum of all the pd must equal the total emf of the circuit

Question 27

true/false: adding a resistor to a circuit in parallel will always reduce the total resistance

Answer 27

true

tot resistance drops the more paths there are for current to take

Question 28

true/false: in parallel circuits the total voltage in each loop is the same

Answer 28

true

Vtot = V1=V2…

Question 29

how does the current vary between each component of a series circuit

Answer 29

the current through all of the components is the same so the current does not vary

Question 30

if you connect two cells in series with positive to positive what will the total emf be

Answer 30

e1+e2

Question 31

true/false: the emf of a source and its terminal voltage will always be the same

Answer 31

false

not all the energy given to the charges in the source makes it out of the cell

Question 32

internal resistance

Answer 32

resistance with in a power source due to the materials and components which make it up

Question 33

lost volts

Answer 33

difference in voltage between that supplied by the source and the amount available to the circuit

Question 34

experiment to determine the internal resistance of a source

Answer 34

set up circuit with a source, ammeter and variable resistor in series and a voltmeter in parallel

vary the resistance and measure the voltage and current

plot graph off V/I

V = -rL + e

internal resiatbce = -m

Question 35

purpose of potential divider

Answer 35

provide variable potential difference or to provide a constant specific potential difference

Question 36

how does voltage across component in a potential divider correspond to its resistance

Answer 36

proportion of the total voltage which is dropped across the component is equal to the proportion of the circuit resistance which its contributes

V/Vt = R/Rt

Question 37

how can a potential divider circuit be used as a sensing circuit

Answer 37

• put resistor that varies with the desired condition in the potential divider
• insert the responding load over either the variable or fixed resistor depending on how the circuit should work