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IGCSE Physics > P3+P9 Electricity > Flashcards

P3+P9 Electricity Flashcards

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1
Q

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

A

FRICTION → TRANSFER OF ELECTRONS

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2
Q

what is a conductor? what makes it a conductor?

A

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

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3
Q

what is an insulator? what makes it an insulator?

A

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

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4
Q

what is current?

A

flow of electrons/rate of flow of charge

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5
Q

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

A

amps (A)

ammeter

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6
Q

how are ammeters connected to a circuit?

A

in series

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7
Q

what is voltage/potential difference/electromotive force?

A

the energy given to each unit of charge

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8
Q

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

A

volts(V)

voltmeter

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9
Q

how are voltmeters connected to a circuit?

A

in parallel

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10
Q

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

A

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

R(total) = R1 + R2 + R3

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11
Q

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

A

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”

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12
Q

what is resistance?

A

opposition to the flow of charge

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13
Q

what is the unit for resistance?

A

ohms(Ω)

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14
Q

longer wire means … resistance? why?

A

more

because current goes a longer distance

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15
Q

thicker wire means … resistance? why?

A

less

because it’s easier for current to go through

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16
Q

what is ohm’s law?

A

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

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17
Q

what would a ohmic graph look like?

A

straight line

through the origin

18
Q

why is a filalamp non-ohmic?

A

it HEATS UP

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

19
Q

what is power?

A

energy transferred per unit time

20
Q

what is the unit for power?

A

watts(W)

21
Q

what are the electricity formulas to remember?

A

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

Q = I t
P = I V

V = I R

22
Q

how do you calculate POWER?

A 
P = E/t
P = IV
23
Q

how do you calculate ENERGY?

A 
E = P t 
E = V I t
E = Q V
24
Q

how do you calculate CURRENT?

A 
I = Q/t
I = V/R
I = P/V
25
Q

how do you calculate VOLTAGE?

A 
V = E/Q
V = I R
V = P/I
26
Q

how do you calculate RESISTANCE?

A

R = V / I

27
Q 
how do you draw...
cell
switch
fixed resistor & variable resistor
lamp
fuse
A

check notes :)

28
Q

what does a VARIABLE RESISTOR do?

A

changes resistance → changes current

29
Q

what is a FUSE and how does it work?

A

safety device

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

30
Q

name and explain the 3 main types of ELECTRICAL HAZARDS

A

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

31
Q

how do you choose fuse rating (maximum current)?

A

just above/same as the current of the device

32
Q

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

A

fuse always melts

33
Q

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

A

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

34
Q

what is a CIRCUIT BREAKER and how does it work?

A

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

*check notes for diagram!

35
Q

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

A

cheap

small (can be put inside all plugs)

36
Q

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

A

reusable (doesn’t melt and break)

move sensitive/reacts quicker

37
Q

what is a LDR and how does it work?

A

light-dependent resistor

light intensity increase → resistance decrease → current increase

38
Q

what is a thermistor and how does it work?

A

temperature-dependent resistor

temp. increase → resistance decrease → current increases

39
Q

what is the symbol for LDR?

A

light shine on circle component

40
Q

what is the symbol for thermistor?

A

hockey stick through rectangle

41
Q

as light intensity increases, resistance through a LDR…

A

decreases

→ current increases

42
Q

as temperature increases, resistance through a thermistor…

A

decreases

→ current increases

IGCSE Physics (9 decks)

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