Circuits

Question 1

describe how the lamp works

Answer 1

electrical current heats the filament lamp in a bulb so that it gives out light

Question 2

describe role of a fixed resistor

Answer 2

restricts or limits flow of electrical charge

Question 3

explain role of variable resistor and what it is used in

Answer 3

modify the amount of resistance in circuit

Question 4

describe resistance in a thermistor

what use thermistors?

Answer 4

depends on its temperature - as temp increases resistance decreases
thermostats and heat activated fire alarms

Question 5

describe resistance in LDR

what contains LDR?

Answer 5

resistance depends on light intensity, at low light ldr has high resistance. as light intensity increases, resistance decreases
can be used in automatic lights

Question 6

explain what a diode does and why its used

Answer 6

allows current to flow only one direction, used to convert alternating current in other direction

Question 7

what is a cell?

Answer 7

store of chemical energy

Question 8

what is a battery?

Answer 8

2 or more cells in series

Question 8

what is the formula for current (not ohms law one)?

Answer 8

charge / time

Question 8

state the formula for charge

Answer 8

current x time

I x t

Question 8

state the formula for potential difference

Answer 8

current x resistance

Question 8

state the formula for resistance

Answer 8

pd / current

v / I

Question 9

state the formula for power transferred

Answer 9

I x v

current x pd

Question 10

state the formula for power absorbed

Answer 10

I2 x R

current squared x resistance

Question 11

what causes resistance?

Answer 11

when electrons collide with ions in the conductor

Question 12

how must voltage be measured?

Answer 12

in parallel

Question 13

what scientific term describes the electrons in a metal when a current flows through it?

Answer 13

delocalised

Question 14

how do you calculate voltage?

Answer 14

current x resistance

Question 15

what does ohms law state?

Answer 15

electric current is proportional to voltage and inversely proportional to resistance

Question 16

how do you find total resistance of a circuit in series?

Answer 16

add all resistors together

R1 + R2 + R3

Question 17

what are the two types of current

Answer 17

direct and alternating current

Question 18

what is direct current

Answer 18

the flow of electrons is consistently in one direction around the circuit

Question 19

what is alternate current

Answer 19

the direction of electron flow continually reverses

Question 20

what is electrical current

Answer 20

a flow of electrons / flow of electrical charge

Question 21

what is charge

Answer 21

amount of electricity travelling in a circuit

Question 22

how do you measure pd across component

Answer 22

voltmeter must be placed in parallel with the component order to measure difference in energy from one side of component to the other

Question 23

how do you measure current through component

Answer 23

ammeter must be placed in series with component

Question 24

what is potential difference

Answer 24

the driving force that pushes the charge around | and a measure of how much energy is transferred between 2 points in a circuit

Question 25

explain the role of a fuse in a circuit

Answer 25

they break/melt if too much current flows through the circuit

Question 26

what do ammeters measure

Answer 26

current

Question 27

in series, the potential difference of the battery is…

Answer 27

shared across all of the components

Question 28

in a series circuit the current is…

Answer 28

the same everywhere in the circuit

Question 29

how do you work out total resistance in a series circuit

Answer 29

add all resistors together

Question 30

what happens if one bulb in a series circuit breaks?

Answer 30

current won’t beable to flow around the circuit so all other bulbs will go out

Question 31

in parallel circuits total current supplied is…

Answer 31

split between all the components on different loops

Question 32

in parallel circuits the potential difference is…

Answer 32

the same across each loop

Question 33

why will adding a resistor to a parallel circuit which already has one resistor decrease the overall resistance?

Answer 33

adding another resistor will also add another loop introducing another possible pathway for current to flow

Question 34

how do you calculate voltage drop

Answer 34

current x resistance

Question 35

state the formula for finding total resistance of a parallel circuit

Answer 35

1/R1 + 1/R2 + 1/R3 + 1/R4

Question 36

once you have added the fractions when working out total resistance of a parallel circuit, what do you need to remember to do?

Answer 36

flip the fraction so you can divide

Question 37

using ohms law how do you work out current in a circuit?

Answer 37

potential difference / resistance

Question 38

a battery is connected in series with a 4 ohms resistor, 5 ohms resistor and a 6 ohms resistor. a current of 0.6A flows through the circuit. calculate the potential difference of the battery

Answer 38

4+5+6=15 | 15 x 0.6 = 9V

Question 39

a series circuit has two resistors of 2 ohms and 3 ohms with a 20V cell. calculate the current passing through the circuit

Answer 39

2+3=5 | 20 / 5 = 4A

Question 40

why does an ohmic conductor graph have a straight line?

Answer 40

the current through an ohmic conductor (at constant temperature) is directly proportional to potential difference so you get a straight line

Question 41

why does a filament graph have a curved line?

Answer 41

as current increases, the resistance increases. the temperature increases as the current flows

Question 42

a diode has a very high resistance in what direction?

Answer 42

reverse

Question 43

what is the 2 formulas for energy transferred!

Answer 43

power x time OR charge x pd

Question 44

what is resistance?

Answer 44

anything that slows the flow down

Question 45

what I-V characteristic does a linear component have? | give an example of a linear component

Answer 45

straight line | fixed resistor

Question 46

what I-V characteristics does a non linear component have? | give an example of a non linear component

Answer 46

curved line | filament lamp

Question 47

what does I-V characteristics refer to?

Answer 47

a graph which shows how the current flowing through a component changes as the potential difference across it is increased

Question 48

state another formula for potential difference (not ohms law)

Answer 48

energy / charge

Question 49

give another formula for potential difference (not ohms law)

Answer 49

energy / charge

Question 50

what is current?

Answer 50

a measure of the flow of electrons around a circuit

Question 51

how does current split between the loops in parallel circuits

Answer 51

loops that have greater resistance receive a lower share of circuits current which is why we get more current flowing in loops with smaller resistance

Question 52

all components in parallel have ... potential difference

Answer 52

the same

Question 53

in series, components with a ... resistance will always have a ... share of voltage

Answer 53

greater

Question 54

what is conventional current?

Answer 54

assumes current flows out of the positive terminal through the circuit and into the negative terminal

Question 55

which terminal do electrons actually flow out of and why

Answer 55

the negative terminal, because electrons are negatively charged they flow around the circuit from the negative terminal to the positive terminal.

Question 56

in terms of battery/cell diagram, which line is the negative terminal and which line is the positive terminal?

Answer 56

negative - shorter line | positive - longer line

Question 57

what are step up transformers and what are the benefits

Answer 57

increases voltage, decreases current | increases efficiency, reduces heat loss

Question 58

what are step down transformers and why are they useful?

Answer 58

decrease voltage, increase current | makes safer for houses