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Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Potential Difference

A

V = W/Q
work done per unit charge to transfer a charge from one point to another

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2
Q

Unit of p.d.

A

Volt (V)/ JC^-1

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3
Q

Electric current

A

the flow of electric charge
I=Q/t

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4
Q

potential at a point

A

p.d. between a point and the earth, where the earth has 0 potential

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5
Q

Capacitance

A

ratio of the charge on a conductor to its p.d.
C=Q/V

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6
Q

Unit for capacitance

A

Farad (F)

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7
Q

Capacitor

A

stores electric charge

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8
Q

Parallel plate capacitor

A

C=εA/d
A=area of overlap between plates
d=distance between plates
ε=permittivity of dialectic (insulator between plates)

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9
Q

Energy stored in charged capacitor

A

equal pos. builds up on one plate and neg. charge on the other. remains when disconnected from power supply. can be discharged by connecting to conductor.
W=½CV²

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10
Q

Size of electric current

A

amount of charge passing any point of a conductor per sec.
Q=It

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11
Q

Conventional Current

A

flows from + to -
(electrons flow opposite direction)

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12
Q

Direct Current

A

flows in one direction, caused by power supply

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13
Q

Alternating Current

A

current constantly reverses direction

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14
Q

Ammeter

A

used to measure current and always connected in series
*galvanometer=microammeter

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15
Q

Voltmeter

A

measures voltage and always connected in parallel with component

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16
Q

Ohmmeter

A

measures resistance (Ω)

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17
Q

Micrometer

A

vernier scale, measures very small distances e.g. thickness of a wire

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18
Q

Power dissipated/electrical power

A

P=VI

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19
Q

voltages in series

A

V=V¹+V²+V³

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20
Q

voltages in parallel

A

V¹=V²=V³

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21
Q

E.M.F.

A

Electromotive force: voltage applied to a circuit

22
Q

Primary cell

A

type of electric cell (converts chem. energy into elec. energy and source of e.m.f.) that can’t be recharged.
Also: dry cells as electrolyte tends to be chem. paste

23
Q

Secondary cell

A

cell that can be recharged. also known as accumulator
e.g. car battery

24
Q

Resistance

A

R=V/I
ratio of p.d. accross conductor to the current flowing through it

25
Q

unit of resistance

A

Ohm (Ω)

26
Q

Ohm’s law

A

V∝I
states that for certain conductors (mainly metals) the current flowing through them is directly proportional to the p.d. accross them at a constant temperature
V=IR

27
Q

Resistors in series

A

R=R¹+R²+R³

28
Q

resistors in parallel

A

1/R=1/R¹+1/R²+1/R³

29
Q

resistivity

A

the material also affects the resistance of a conductor by a fixed amount for different materials (resistivity)
R=ρL/A
ρ=Rπd²/4L

30
Q

unit for resistivity

A

omh meter

31
Q

Electrolysis

A

the chemical effect of an electric current

32
Q

inactive electrodes

A

electrodes that don’t take part in the chemical reaction e.g. platinum in SO⁴

33
Q

Active electrodes

A

electrodes that take part in the chemical reaction e.g. copper in CuSo⁴

34
Q

Anode

A

positive

35
Q

cathode

A

negative

36
Q

voltameter

A

electrodes, electrolyte and container

37
Q

ion

A

an atom or molecule that has lost or gained one or more electrons

38
Q

MCB

A

miniature circuit breaker. found in distribution box.
bimetallic strips (small currents) or electromagnets (large currents).
can be reset when switch trips, faster than fuse

39
Q

RCD

A

residual current device: protects sockets and people against electrocution by detecting a difference between current in live and neutral wire (30mA)

40
Q

Bonding

A

all metal taps, pipes, water tanks etc. are connected to the earth

41
Q

Earthing

A

earth wire prevents electrocution from touching metal parts of appliances by providing a path of least resistance when faults occur

42
Q

Fuse

A

piece of wire that will melt when a current of a certain size passes through it. connected to the live wire

43
Q

application of joule’s law

A

in order to prevent power lines from overheating, electricity transmitted at very high voltage (EHT: extra high tension)
i.e. transformer used to increase voltage and lower current/heat

44
Q

Joule’s Law

A

P∝I²
rate at which heat is produced in a conductor is directly proportional to the square of the current if resistance is constant.
P=I²R

45
Q

Factors affecting resistance

A
  1. temperature
  2. length
  3. material
  4. cross-sectional area
46
Q

resistance and length

A

R∝L

47
Q

resistance and area

A

R∝1/A

48
Q

Wheatstone bridge

A

R¹/R²=R³/R⁴ when balanced

49
Q

metre bridge

A

R¹/R²= |AD|/|DC|

50
Q

uses of wheatstone bridge

A
  1. temperature control
  2. fail safe device
  3. measure unknown resistance

Physics (12 decks)

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