Electricity

Question 1

Potential Difference

Answer 1

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

Question 2

Unit of p.d.

Answer 2

Volt (V)/ JC^-1

Question 3

Electric current

Answer 3

the flow of electric charge
I=Q/t

Question 4

potential at a point

Answer 4

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

Question 5

Capacitance

Answer 5

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

Question 6

Unit for capacitance

Answer 6

Farad (F)

Question 7

Capacitor

Answer 7

stores electric charge

Question 8

Parallel plate capacitor

Answer 8

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

Question 9

Energy stored in charged capacitor

Answer 9

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

Question 10

Size of electric current

Answer 10

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

Question 11

Conventional Current

Answer 11

flows from + to -
(electrons flow opposite direction)

Question 12

Direct Current

Answer 12

flows in one direction, caused by power supply

Question 13

Alternating Current

Answer 13

current constantly reverses direction

Question 14

Ammeter

Answer 14

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

Question 15

Voltmeter

Answer 15

measures voltage and always connected in parallel with component

Question 16

Ohmmeter

Answer 16

measures resistance (Ω)

Question 17

Micrometer

Answer 17

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

Question 18

Power dissipated/electrical power

Answer 18

P=VI

Question 19

voltages in series

Answer 19

V=V¹+V²+V³

Question 20

voltages in parallel

Answer 20

V¹=V²=V³

Question 21

E.M.F.

Answer 21

Electromotive force: voltage applied to a circuit

Question 22

Primary cell

Answer 22

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

Question 23

Secondary cell

Answer 23

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

Question 24

Resistance

Answer 24

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

Question 25

unit of resistance

Answer 25

Ohm (Ω)

Question 26

Ohm's law

Answer 26

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

Question 27

Resistors in series

Answer 27

R=R¹+R²+R³

Question 28

resistors in parallel

Answer 28

1/R=1/R¹+1/R²+1/R³

Question 29

resistivity

Answer 29

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

Question 30

unit for resistivity

Answer 30

omh meter

Question 31

Electrolysis

Answer 31

the chemical effect of an electric current

Question 32

inactive electrodes

Answer 32

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

Question 33

Active electrodes

Answer 33

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

Question 34

Anode

Answer 34

positive

Question 35

cathode

Answer 35

negative

Question 36

voltameter

Answer 36

electrodes, electrolyte and container

Question 37

ion

Answer 37

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

Question 38

MCB

Answer 38

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

Question 39

RCD

Answer 39

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

Question 40

Bonding

Answer 40

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

Question 41

Earthing

Answer 41

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

Question 42

Fuse

Answer 42

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

Question 43

application of joule's law

Answer 43

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

Question 44

Joule's Law

Answer 44

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

Question 45

Factors affecting resistance

Answer 45

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

Question 46

resistance and length

Answer 46

R∝L

Question 47

resistance and area

Answer 47

R∝1/A

Question 48

Wheatstone bridge

Answer 48

R¹/R²=R³/R⁴ when balanced

Question 49

metre bridge

Answer 49

R¹/R²= |AD|/|DC|

Question 50

uses of wheatstone bridge

Answer 50

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