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Physics > P4 - Electricity > Flashcards

P4 - Electricity Flashcards

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1
Q

electric field

A

region in which an electric charge experiences a force

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2
Q

for a positive charge, what direction would the force be experienced?

A

outwards

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3
Q

for a negative charge, what direction would the force be experienced?

A

inwards

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4
Q

electric current

A

charge passing a point pre unit time

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5
Q

electrostatic charge

A

materials’ charge

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6
Q

where does electric charge come from?

A

batteries and generators / if rubbed

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7
Q

what 2 materials can used to create charge?

A

polythene (becomes -ve) and perspex (becomes +ve)

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8
Q

closer the charges, _____ the _____ between them

A

greater force

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9
Q

what does rubbing materials do?

A

seperates charges that are already there

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10
Q

conductors and examples?

A

materials that let electrons pass through them as they have free electrons between indivisual atoms
-ex copper, gold, metals, carbon

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11
Q

insulators and examples?

A

materials that dont conduct as electrons are tightly held by atoms and are not free. (but it can be transferred by rubbing and once transferred, it stays. and its easy to charge)
-ex: plastics, glass, dry air

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12
Q

semi-conductors and examples?

A

materials that are poor conductors when cold, good conductors when warm
-ex: silicon, germanium

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13
Q

direction of conventional current? flow of electrons?

A

positive to negative / negative to positive

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14
Q

earthing

A

connected to the ground by conducting materials so that unwanted charges flow away. if this is not done, electrons may be pulled through the air and cause dangerous sparks

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15
Q

voltage

A

cause of current in the circuit

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15
Q

induced charges

A

appear on an unchanged object because there’s a charged object nearby (opposite charges)

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16
Q

what can electrostatic charge be detected by?

A

leaf electroscope

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17
Q

static electricity

A

charges that are not free to move (build up in one place, shock when they move) (build up of charge on insulating materials)

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18
Q

static electrcity uses [3]

A

-electrostatic smoke precipitators (dust attracts to the charged plates)
-spray painting (spray drop is +ve, drops repela and spread out, earth is -ve and the car is connected to earth, drops attracted to the car)
-photocopiers (black toner attracted to paper)

19
Q

emf

A

electricatl work done by a source in moving a unit charge around a complete circuit (V) (across cell)

20
Q

pd

A

work done by a unit charge passing between two points in a circuit (V) (across device)

21
Q

resistance

A

ratio of voltage to current in an appliance (measures load)

22
Q

how to measure emf?

A

voltmeter across cell

23
Q

how to measure pd?

A

voltmeter across appliance (device)

24
Q

if resistance is greater, what happens to voltage and current?

A

resistance increases, voltage increases, current decreases

25
Q

resistance formula

A

voltage / current

26
Q

current formula

A

charge / time (I=Q/t)

27
Q

what is Ohm’s law?

A

current is directly proportionate to Voltage (V increases, I increases)

28
Q

what are ohmic conductors? examples? graph?

A

conductors that follow Ohm’s law
-examples: metallic conductors at room temperature
-I-V graph is a straight line through the origin

29
Q

Non-Ohmic conductors? graph?

A

conductors that don’t follow Ohm’s law
-I-V graph is not a straight line through the origin

30
Q

relation between length and resistance

A

resistance is directly proportionate to length (longer the wire, more resistance)

31
Q

relation between area and resistance

A

resistance is inversely proportionate to area (thin wire, large resistance / thick wire, small resistance)

32
Q

what happens to resistance if area doubles?

A

resistance halves

33
Q

what happens to resistance if radius doubles?

A

decreases by 4 times

34
Q

formula for volts

A

energy / charge (coulombs)

35
Q

formula for energy

A

(voltage x current = power) x time

36
Q

formula for power (energy)

A

energy / time

37
Q

formula for power (voltage)

A

voltage x current (amps)

38
Q

unit for energy (power flow with time)

A

kilowatt-hour (kwh)

39
Q

what is a variable resistor

A

helps introduce varying resistance in the circuit

40
Q

HOW DOES LIGHT DEPENDANT RESISTOR AFFECT RESISTANCE?

A

LIGHT INTENSITY INCREASES, RESISTANCE DECREASES (DARK = MORE RESISTANCE) (CURVED LINE C ON GRAPH THOUGH)

41
Q

what do electric circuits do?

A

transfer energy from a source of electrical energy (electrical cell or mains supply) to the circuit components and then into the surroundings

42
Q

total resistance of series circuit

A

R1 + R2 + R3

43
Q

4 features of series circuit

A

-voltage is divided
-if one disconnects all don’t work
-current is the same anywhere (ampmeter)
-V1 + V2 + V3 = supply voltage (EMF)

44
Q

total resistance in parallel circuit

A

1/R1 + 1/R2
-total resistance is less than smallest resistance (each resistor)

45
Q

5 features of parallel circuit

A

-current splits up in proportion do resistance in each branch (larger resistance, larger current)
–> I1 + I2 = I
-each branch gets same voltage as supply
-used in domestic wiring
-if one disconnects, others still work
-current from source is larger than current in each branch

46
Q

short circuit

A

huge current goes through (no resistor) and could cause a fire

Physics (13 decks)

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