Electric Circuits

Question 1

what is the purpose of a switch?

Answer 1

to turn a circuit on (closed) or off (open)

Question 2

how does a lamp work?

Answer 2

an electrical filament heats the filament inside a bulb so that it gives out light

Question 3

what is a resistor?

Answer 3

it restricts or limits the flow of electrical current. a fixed resistor has a resistance that doesn’t change while a variable resistor’s resistance can be changed by moving a slider on the resistor

Question 4

what is a thermistor?

Answer 4

it has a resistance that changes based on temperature - the colder it is, the higher the resistance

Question 5

what is an LDR?

Answer 5

Light Dependent Resistor - resistance changes depending on light intensity - the lower the light intensity, the higher the resistance

Question 6

what is the purpose of a semiconductor diode?

Answer 6

it allows current to flow in one direction only

Question 7

what does a voltmeter do?
how do you connect it to a circuit?

Answer 7

• it measures potential difference
• you connect it in parallel (across the component)

Question 8

what does an ammeter do?
how do you connect it to a circuit?

Answer 8

• it measures current
• you connect it in series (in line with the component)

Question 9

how do you know if a circuit is complete?

Answer 9

if you can follow a wire from one end of the power supply, through the components, to the other end of the power supply, it is complete

Question 10

what are the 2 types of current and describe them

Answer 10

• direct current - electrons flows in one direction only
• alternating current - direction of electron flow continually reverses

Question 11

what is an electron?

Answer 11

it is a negatively charged particle that transfers energy through a wire as electricity

Question 12

what is charge?

Answer 12

it is a property of certain objects like electrons and protons - they experience a force when in electric fields

Question 13

how is charge measured?
bonus: how many electrons are in each of these?

Answer 13

• coulombs
• 1 coulomb = 6.25 x 10^18 electrons

Question 14

what is current?

Answer 14

the rate of flow of electric charge

Question 15

in what direction does current flow in an electric circuit?

Answer 15

it flows from positive to negative

Question 16

what is the formula to calculate the amount of charge passing a point in the circuit?

Answer 16

charge = current x time
Q = It

Q = C
I = A
t = s

Question 17

in a series circuit, current…

Answer 17

…is the same everywhere

Question 18

how would you describe one amp?

Answer 18

the current that flows when one coulomb of charge passes a point in the circuit in one second

Question 19

what 2 things does the current flowing through a component depend on?

Answer 19

• resistance of the component
• potential difference across the component

Question 20

current will only flow through a circuit if there is…

Answer 20

…potential difference

Question 21

what is potential difference?

Answer 21

it measures the amount of energy transferred per unit of charge

Question 22

what is the unit of potential difference?

Answer 22

Volts (V)

Question 23

1 V = ?

Answer 23

1 Joule per Coulomb

Question 24

what is the formula to calculate potential difference?

Answer 24

potential difference = energy / charge
V = E/Q

V = V
E = J
Q = C

Question 25

what is resistance?

Answer 25

anything in the circuit which reduces the flow of current

Question 26

what is resistance measured in?

Answer 26

ohms (Ω)

Question 27

the larger the resistance...

Answer 27

...the smaller the current

Question 28

what is the formula linking resistance, potential difference and current?

Answer 28

potential difference = current x resistance V = IR V = V I = A R = Ω

Question 29

what are the relative resistances of conductors and insulators?

Answer 29

- conductors = low resistance - insulators = high resistance

Question 30

what is an ohmic conductor?

Answer 30

a device that obeys Ohm's Law like wires or resistors

Question 31

what is Ohm's Law?

Answer 31

current and potential difference are directly proportional

Question 32

as temperature of the filament in a filament bulb increases...

Answer 32

...resistance of the filament increases

Question 33

why do diodes not let current flow in the opposite direction?

Answer 33

it has a very high resistance in the reverse direction

Question 34

what are some components that are not ohmic conductors? how do their resistances change?

Answer 34

- lamps, diodes, thermistors and LDRs - resistance changes with current flowing through the component

Question 35

what are the uses of thermistors?

Answer 35

- thermostats - resistance varies with temperature so you can detect temperature of the thermistor and the surroundings - can be used in a car engine to prevent overheating

Question 36

what are the uses of LDRs?

Answer 36

- automatic night lights/outdoor lights - light levels fall, resistance of the LDR increases which triggers the light to turn on - burglar detectors - light is shone down. If the burglar steps in front of it and breaks the light beam, resistance of LDR shoots up and triggers an alarm

Question 37

what are the 2 ways you can set up a circuit?

Answer 37

- in series - in parallel

Question 38

how does current flow in a series circuit?

Answer 38

current is the same everywhere I1 = I2 = I3 ...

Question 39

what would happen if one bulb blew out in a series circuit?

Answer 39

current wouldn't be able to flow around the circuit - the circuit would be broken

Question 40

how does pd work in a series circuit?

Answer 40

- energy is transferred from the power supply and is shared all across the circuit - total pd = sum of all pds across all components - total V = V1 + V2...

Question 41

how does resistance work in a series circuit?

Answer 41

- current has to flow through all the resistors so pd is shared across all of them - total resistance is all the resistances added together - total R = R1 + R2 ...

Question 42

what happens if a component breaks in a parallel circuit?

Answer 42

not much - only components on that branch would be affected. The other branches are independent of each other

Question 43

how does current work in parallel circuits?

Answer 43

- current splits as it leaves the cell and goes into one of the loops - total current is the currents of each branch added together - total I = I2 + I3 + I4 ...

Question 44

how does pd work in parallel circuits?

Answer 44

- each branch gets the same pd as the source so pd is the same across all components - total V = V1 + V2 + V3 ...

Question 45

how does resistance work in parallel circuits?

Answer 45

- imagine 2 resistors are connected in parallel - both resistors have the same pd across them - but becuase of the extra branch, current has more than one path to go through - more total current can flow through the circuit - using V = IR, an increase in current means a decrease in the total resistance of a circuit

Question 46

is it possible to have components connected in series and in parallel in the same circuit?

Answer 46

yes

Question 47

which is more commonly used in actual things: parallel circuits or series circuits?

Answer 47

parallel circuits - everything can be turned on and off separately

Question 48

what is the formula for power in electric circuits?

Answer 48

power = current x potential difference OR power = current^2 x resistance P = IV or P = I^2R P = W I = A V = V R = Ω

Question 49

how is energy transferred in electric circuits?

Answer 49

- as electrons flow through wires, they collide with ions in the wire, causing the ions to vibrate more - increased ion vibration = increased wire temperature - energy is transferred: chemical energy store of battery -> internal energy store of wire

Question 50

1W = ?

Answer 50

1J/s

Question 51

what 2 ways can electric power be transferred?

Answer 51

- low current with high voltage - high current with low voltage

Question 52

what is the most efficient way of transmitting electricity and why?

Answer 52

- at a high voltage with a low current - wires stay cooler - high current has a higher heating effect on the wires so more energy is lost as heat energy