P3+P9 Electricity

Question 1

what happens when you rub a dry cloth against a polythene rod? (2)

Answer 1

FRICTION → TRANSFER OF ELECTRONS

Question 2

what is a conductor? what makes it a conductor?

Answer 2

allows charges to pass through easily cuz its electrons can move freely

Question 3

what is an insulator? what makes it an insulator?

Answer 3

substance that doesn’t allow charges to pass through them easily (cuz its electrons are bonded)

Question 4

what is current?

Answer 4

flow of electrons/rate of flow of charge

Question 5

what is the unit for current and what is used to measure it?

Answer 5

amps (A)

ammeter

Question 6

how are ammeters connected to a circuit?

Answer 6

in series

Question 7

what is voltage/potential difference/electromotive force?

Answer 7

the energy given to each unit of charge

Question 8

what is the unit for voltage and what is used to measure it?

Answer 8

volts(V)

voltmeter

Question 9

how are voltmeters connected to a circuit?

Answer 9

in parallel

Question 10

what happens to current, voltage and resistance in a SERIES circuit?

Answer 10

A (total) = A1 = A2 = A3 (same)
V(total) = V1 + V2 + V3 (shared)

R(total) = R1 + R2 + R3

Question 11

what happens to current, voltage and resistance in a PARALLEL circuit?

Answer 11

A (total) = A1 + A2 + A3 (shared)
V(total) = V1 = V2 = V3 (same)

R(total) = R1 • R2 • R3 / R1 + R2 + R3
“鸡在河上飞 积在和上飞”

Question 12

what is resistance?

Answer 12

opposition to the flow of charge

Question 13

what is the unit for resistance?

Answer 13

ohms(Ω)

Question 14

longer wire means … resistance? why?

Answer 14

more

because current goes a longer distance

Question 15

thicker wire means … resistance? why?

Answer 15

less

because it’s easier for current to go through

Question 16

what is ohm’s law?

Answer 16

the VOLTAGE across a conductor is DIRECTLY PROPORTIONAL to the CURRENT through it as long as the temperature remains the same
→ V = I R

Question 17

what would a ohmic graph look like?

Answer 17

straight line

through the origin

Question 18

why is a filalamp non-ohmic?

Answer 18

it HEATS UP

as temperature increases, the metal particles vibrate more, making it harder for current to pass through

Question 19

what is power?

Answer 19

energy transferred per unit time

Question 20

what is the unit for power?

Answer 20

watts(W)

Question 21

what are the electricity formulas to remember?

Answer 21

E = V Q = V I t = P t
(vitamin E)

Q = I t
P = I V

V = I R

Question 22

how do you calculate POWER?

Answer 22

P = E/t
P = IV

Question 23

how do you calculate ENERGY?

Answer 23

E = P t 
E = V I t
E = Q V

Question 24

how do you calculate CURRENT?

Answer 24

I = Q/t
I = V/R
I = P/V

Question 25

how do you calculate VOLTAGE?

Answer 25

V = E/Q
V = I R
V = P/I

Question 26

how do you calculate RESISTANCE?

Answer 26

R = V / I

Question 27

how do you draw...
cell
switch
fixed resistor & variable resistor
lamp
fuse

Answer 27

check notes :)

Question 28

what does a VARIABLE RESISTOR do?

Answer 28

changes resistance → changes current

Question 29

what is a FUSE and how does it work?

Answer 29

safety device

melts and breaks the circuit when too much current flows → protects cable from overheating and catching fire

Question 30

name and explain the 3 main types of ELECTRICAL HAZARDS

Answer 30

damaged insulation:
touch → electric shock

damp condition:
water conducts electricity → electric shock

overheating cables:
too much current → heat up → insulation melt → poisonous fume + catch fire

Question 31

how do you choose fuse rating (maximum current)?

Answer 31

just above/same as the current of the device

Question 32

what happens when you need 10A, but fuse is 5A?

Answer 32

fuse always melts

Question 33

what happens when you need 10A, but fuse is 100A?

Answer 33

fuse won’t melt even when current’s already too high

Question 34

what is a CIRCUIT BREAKER and how does it work?

Answer 34

too much current → MF strong enough to attract iron latch → opens switch → breaks circuit

*check notes for diagram!

Question 35

what are the advantages of using a FUSE instead of a circuit breaker?

Answer 35

cheap

small (can be put inside all plugs)

Question 36

what are the advantages of using a CIRCUIT BREAKER instead of a fuse?

Answer 36

reusable (doesn’t melt and break)

move sensitive/reacts quicker

Question 37

what is a LDR and how does it work?

Answer 37

light-dependent resistor

light intensity increase → resistance decrease → current increase

Question 38

what is a thermistor and how does it work?

Answer 38

temperature-dependent resistor

temp. increase → resistance decrease → current increases

Question 39

what is the symbol for LDR?

Answer 39

light shine on circle component

Question 40

what is the symbol for thermistor?

Answer 40

hockey stick through rectangle

Question 41

as light intensity increases, resistance through a LDR…

Answer 41

decreases

→ current increases

Question 42

as temperature increases, resistance through a thermistor…

Answer 42

decreases

→ current increases