electricity

Question 1

what is current

Answer 1

rate of flow of charge

Question 2

what is conventional current

Answer 2

positive to negative

Question 3

what is a coulomb

Answer 3

the amount of charge that passes in 1 second if the current is 1 ampere

Question 4

what is potential difference

Answer 4

energy per unit charge or work done per unit charge moved

Question 5

what is the definition of a volt

Answer 5

the potential difference across one component is 1 volt when you convert 1 joule of energy moving 1 coulomb of charge through a component

Question 6

what is an ohm

Answer 6

a component with a resistance of 1 ohm if the potential difference is 1V making a current of 1A flow

Question 7

what is an ohmic conductor

Answer 7

conductors that obey ohms law are called ohmic conductors and this means that provided physical conditions, such as temperature, remain constant the current through an ohmic conductor is directly proportional to the potential difference across it

Question 8

what do I/V graphs show

Answer 8

how the resistance varies as current changes as the PD is increased

Question 9

what is the difference between a I/V graph and a V/I graph

Answer 9

V/I is V plotted again I
I/V is I against V

Question 10

what will a I/V graph look like for an ohmic conductor

Answer 10

a straight line through the origin

Question 11

what does a IV graph look like for a filament lamp

Answer 11

an s curve that starts steep but gets shallower

Question 12

why are filament lamp on a I/V graph not just like a metallic conductor

Answer 12

the filament lamp is a coiled up length of wire so as the current flowing through the lamp increases its temperature increasing its resistance

Question 13

how can semiconductors be used for sensors

Answer 13

semiconductors are not as good at conducting electricity as metal because the have much less charge carriers. however is energy is supplied more charge carriers can be released this mean they work excellent as sensors detecting change in the environment

Question 14

what are the two semiconductors we need to know about

Answer 14

thermistors and diodes

Question 15

what does a thermistor look like on a I/V graph and why

Answer 15

a curve and s curve starting shallow and getting steeper as current increases the temperature increases.
this is because they are NTC thermistors which means as temperature goes up resistance decreases

Question 16

what do diodes do

Answer 16

only let current flow in one direction .

Question 17

what is the forwards bias of a diode

Answer 17

the direction the current is allowed to flow

Question 18

what is the general threshold of a diode in the forward bias

Answer 18

roughly 0.6V in the forward direction before they will conduct

Question 19

what happens if the current flow through the reverse bias of a diode

Answer 19

the resistance is very high and the current very low

Question 20

what do diodes look lie on a IV graph

Answer 20

almost perfectly flat with the ever so slightest tilt upwards up to 0.6 where is shoots upwards

Question 21

what are the three things you need to determine resistance

Answer 21

1- length the longer the wire the more difficult it is to make current flow
2- area the wider the wire the easier it is for electrons to pass through
3- resistivity which depends on the materials structure and may make it harder or easier for current to flow. resistivity also depends on environmental factors as well like temperatures and light intensity

Question 22

what is the definition of resistivity

Answer 22

the resistance of 1m length with 1m^2 cross-sectional area it is measured in ohm meters

Question 23

what are superconductors

Answer 23

materials with no resistivity.

Question 24

why are super conductors better

Answer 24

no energy is wasted as thermal energy

Question 25

how do we make super conductors

Answer 25

lowering materials bellow their critical temperature

Question 26

what is the downside of superconductors

Answer 26

have to be kept at a low temperature which is expensive

Question 27

what are the uses of super conductors

Answer 27

1- power cables 2-really strong electromagnets that doesn't need a constant power source 3-elctronic circuits that work really fast, because theirs no resistance to slow them down

Question 28

what is power

Answer 28

the rate of transfer of energy measured in watts where 1 watt is equivalent to 1 joule per second

Question 29

how do batteries have resistance

Answer 29

resistance come from electrons colliding with atoms and losing energy to other forms. in a battery chemical energy is what makes electrons move. as they move they collide with atoms inside the battery causing resistance. this called the internal resistance.

Question 29

how can you calculate energy from power

Answer 29

energy is just power multiplied by time

Question 30

what is the e.m.f

Answer 30

the amount of electrical energy the battery produces for each coulomb of charge and is measured in volts

Question 31

what is the load resistance

Answer 31

the total resistance of all the components in the external circuit

Question 32

what is the terminal p.d

Answer 32

the energy transferred when one coulomb of charge travels through the load resistance

Question 33

what is the lost volts

Answer 33

the energy wasted per coulomb over coming the internal resistance

Question 34

what is conservation of energy

Answer 34

energy per coulomb supplied by the source = energy transferred in load resistance + energy per coulomb wasted in internal resistance

Question 35

what is something you can do to the e.m.f equation

Answer 35

multiply it out and them manipulate it by adding in V=IR for either the internal or external to find an equation with everything you've got

Question 36

how do you get the emf for multiple cells in series

Answer 36

add up the individual emfs

Question 37

how do you get the emfs for multiple cells in parallel

Answer 37

for identical cells in parallel the emf is equal to one individual cell

Question 38

what is Kirchhoff's first law

Answer 38

the total current entering a junction is equal to the current leaving it charge is conserved

Question 39

what is Kirchhoff's second law

Answer 39

the total emf around a series circuit is equal to the sum of the pds across each component

Question 40

how do Kirchhoff's rules relate to a series circuit

Answer 40

according to his second rule the emf is equal to all the individual voltages. and since V=IR the the total IR is equal to each IR so I is constant cancelling I gives Rt=R1+R2+R3

Question 41

how do Kirchoffs law relate to parallel circuits

Answer 41

we know that the current is split at each junction which means V/Rt=V/R1+V/R2 cancelling V gives 1/Rt=1/R1+1/R2

Question 42

what is a potential divider circuit

Answer 42

a circuit with a voltage source and a couple resistors in series

Question 43

what happens in a potential divider circuit

Answer 43

the potential difference is split in the ratio of the resistors

Question 44

how can you figure out he voltage out across potential dividers in a circuit

Answer 44

R2/R1+R2 x Vs which is essentially figuring out the ratio between R1and R2

Question 45

what changes the resistance of a LDR

Answer 45

high resistance in dark and low in light

Question 46

what can you do with LDRs and thermistors in a potential divider circuit

Answer 46

swap the second resistor with one to create a sensor when the temperature increase the temperature or increase light levels the resistance across R2 will drop causing the R1 t increase and V out t increase in turn

Question 47

what is a potentiometer what doe sit do and why is it useful

Answer 47

its essential the two resistors from a potential divider circuit connected and you can turn the nob to adjust the sizes of R1 and R2 inversely proportionally this is cool for doing something like adjusting volume as you can control V out