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Physics > Electricity 2 > Flashcards

Electricity 2 Flashcards

1
Q

Current

A

The flow of charge

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2
Q

3 examples of current

A

passage of electrons along a copper wire
motion of ions between electrodes in a solution
motion of positive holes and electrons in a semiconductor

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3
Q

current is also known as

A

charge per unit time passing a point

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4
Q

I =

A

Q/t

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5
Q

I

A

resistance

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6
Q

Q

A

charge

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7
Q

t

A

time

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8
Q

unit of I

A

Ampere (A)

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9
Q

unit of Q

A

Coulumb (C)

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10
Q

1 ampere =

A

1 Coulumb/1 second

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11
Q

modern current name

A

actual current

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12
Q

old-style current name

A

conventional current

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13
Q

which direction does conventional current flow?

A

positive to negative

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14
Q

in which direction does actual current flow?

A

negative to positive

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15
Q

easy explanation of current

A

number of electrons flowing in the wire

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16
Q

easy explanation of voltage

A

ability of electrons to do a task

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17
Q

how to find number of electrons

A

total charge / charge on one electron

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18
Q

what did ohm notice?

A

potential difference was directly proportional to the current if the temperature remained constant

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19
Q

what is resistance

A

the voltage across a conductor divided by the current flowing through

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20
Q

3 factors affecting resistance

A

length
resistivity
1/cross sectional area

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21
Q

p=

A

RA/l

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22
Q

p

A

resistivity

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23
Q

R

A

resistance

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24
Q

A

A

cross sectional area

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25
Q

definition of resistivity

A

the resistivity of a conductor is the resistance of the conductor of length 1m and cross-sectional area of 1 m squared

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26
Q

unit of resistivity

A

ohm meter

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27
Q

cross-sectional area

A

pi r squared

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28
Q

diameter

A

2r

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29
Q

what do you measure the diameter with?

A

micrometer

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30
Q

name of thing that olds wire in place when measuring diameter

A

grip/teeth

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31
Q

what do you tighten teeth when measuring diameter

A

slip control

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32
Q

how do you measure diameter accurately on the wire

A

take several measurements down the wires and get the average

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33
Q

how to calculate resistivity in the experiment

A

p= R x pi r squared / l

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34
Q

1 more accuracy technique in experiment of measuring resistivity

A

avoid small values of length beacuse measuring small values of length, result in greater percentage error

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35
Q

length and resistance graph, whats on x-axis

A

length

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36
Q

length and resistance graph, whats on y-axis

A

resistance

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37
Q

length and resistance graph, whats the resistivity

A

slope x pi r squared

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38
Q

tiny notches on vernier scale go up in

A

2s

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39
Q

2 scales on micrometer

A

main scale

vernier scale

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40
Q

what do you have to make sure before you measure the length of a wire

A

make sure it’s straight and taut

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41
Q

what do you check on micrometer before measuring

A

check the zero error

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42
Q

(2) higher temperature=

A

increase in resistance

increase in diameter

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43
Q

how do you use a wheatstone bridge

A

by trial and error change the values of the resistors in the circuit until the galvanometer reads zero

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44
Q

wheatstone bridge culculation

A

R1/R2 = R3/R4

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45
Q

wheatstone bridge top left

A

R1

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46
Q

wheatstone bridge bottom left

A

R3

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47
Q

wheatstone bridge top right

A

R2

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48
Q

wheatstone bridge bottom right

A

R4

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49
Q

advantage of wheatstone bridge

A

compact

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50
Q

disadvantage of wheatstone bridge

A

expensive

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51
Q

how do you use a meter bridge

A

the sliding contact is moved along the uniform resistance wire until the galvanometer reads zero

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52
Q

meter bridge calculation

A

Rx x I2 = Ry x I1

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53
Q

meter bridge top left

A

Rx

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54
Q

meter bridge top right

A

Ry

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55
Q

meter bridge bottom left

A

I1

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56
Q

meter bridge bottom right

A

I2

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57
Q

advantage of meter bridge

A

very accurate

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58
Q

disadvantage of meter bridge

A

very large

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59
Q

advantage of ohmmeter

A

fast

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60
Q

disadvantage of ohmmeter

A

less accurate

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61
Q

2 practical uses wheatstone bridge

A

temporary control

fail safe device

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62
Q

explain temporary control as a wheatstone bridge

A

to maintain a room at a fixed temperature

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63
Q

how is a fail safe device a wheatstone bridge

A

to prevent poisonous leaking from a boiler

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64
Q

explain the fail safe gas boiler system

A
  • thermistor positions above the flame
  • if the flame goes out then the resitance changes and wheatstone bridge is no longer balanced
  • current flows through and is used to turn off a switch which cuts off the gas supply,
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65
Q

why do you need a failsafe device in a gas boiler

A

because if the gas didnt burn it could seep into the house and it is poisonous

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66
Q

resistors in series

A

Rt = R1 + R2 + R3

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67
Q

resisitors in parallel

A

1/Rt = 1/R1 + 1/R2 + 1/R3

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68
Q

combining resistors in series

A

bigger resistance

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69
Q

combining resistors in parallel

A

smaller resistance

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70
Q

6 steps in in long question

A
  1. resistance in parallel
  2. total resistance (in series)
  3. find total current
  4. find voltage across AB
  5. therefore voltage across BC
  6. current in that one resistor
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71
Q

steps for calculating current flowing through a certain resistor

A

calculate resistance in parallel (1/Rt etc)
total resistance in series
total current (I=V/R)
voltage across resistors in series (Vab=IxR)
therefore voltage left for other resistors (total - ^^^)
current in that resistor (I = V/R)

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72
Q

moving the sliding contact of a potential divider up as much as possible gives a voltage of…

A

whatever the battery is

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73
Q

moving the sliding contact of a potential divider down as much as possible gives a voltage of…

A

0 V

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74
Q

ratio of voltage divided in what ratio?

A

the resistance values

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75
Q

emf

A

electromotive force

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76
Q

symbol of emf

A

E

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77
Q

unit of emf

A

Volt

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78
Q

what is emf

A

the same as potential difference but only for things that make their own electricity

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79
Q

3 sources of emf

A

an electric cell (battery)
ESB mains
a thermocouple

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80
Q

what does emf depend on in a battery

A

it depends on the chemicals used in the cell

81
Q

what is the emf of the ESB mains?

A

230 V

82
Q

what does the emf depend on in a thermocouple

A

the material of the two wires and the temperature difference between the ends on the wires

83
Q

sliding contact of a potential divider

A

long rectangle

84
Q

symbol for voltameter

A

V in a circle

85
Q

symbol for milliammeter

A

mA in a circle

86
Q

graph of voltage and current, which is on x-axis?`

A

voltage

87
Q

graph of voltage and current, which is on y-axis

A

current

88
Q

graph of voltage and current for metallic conductor (wire)

A

straight line graph through the origin

89
Q

what must remain constant in current and voltage against a wire?

A

temperature must remain constant

90
Q

3 factors of accuracy in metallic conductor (wire) experiment

A
  • avoid large currents, causes wire to heat up, non linear graph
  • ensure good electrical contacts, poor contacts causes variation in resistance
  • check voltmeter and milliammeter for zero error and correct
91
Q

symbol for a filament bulb

A

a rainbow shape with a circle around it

92
Q

3 steps in sliding contacts experiments

A
  • adjust sliding contact until voltmeter reads zero
    record milliammeter value
  • adjust until voltmeter reads one and record milliammeter value
  • do the same for 2V, 3V, 4V etc.
93
Q

3 notes on accuracy

A
  • avoid very low currents, bulb will blow
  • good electrical contacts, or there will be variations in resistance
  • check voltmeter and milliammeter for 0 error and correct if necessary
94
Q

graph of filament bulb experiment

A

non-linear

95
Q

what does it mean that filament bulb graph is non-linear?

A

Ohm’s law is not obeyed

96
Q

why is ohm’s law not obeyed in filament bulb experiment?

A

current increases, temperature increases, increased thermal vibrations in the atoms of the filament
more difficult for the electrons to flow through the filament, resistance of the filament increases

97
Q

To investigate the variation of the resistance of a metallic conductor with temperature
WHAT LIQUID IS IN THE BEAKER

A

glycerol

98
Q

To investigate the variation of the resistance of a metallic conductor with temperature
THE TEMPERATURE OF THE METALLIC CONDUCTOR IS THE SAME AS

A

the temperature of the oil

99
Q

To investigate the variation of the resistance of a metallic conductor with temperature
WHAT’S ON THE Y AXIS?

A

RESISTANCE

100
Q

To investigate the variation of the resistance of a metallic conductor with temperature
X-AXIS

A

TEMPERATURE

101
Q

To investigate the variation of the resistance of a metallic conductor with temperature
2 POINTS ON ACCURACY

A

check ohmmeter for zero error and correct if necessary

ensure good electrical contacts between the metallic conductor and the ohmmeter as poor electrical contacts cause a variation in resistance

102
Q

Heat = (2)

A

V I t

I² R t

103
Q

Power = (2)

A

V I

I²R

104
Q

unit of energy by ESB

A

kilowatt hour

105
Q

units of energy =

A

kilowatts x hours

106
Q

current has a (2)

A

current has a heating effect

current has a magnetic effect

107
Q

practical example to show the heating effect of electricity

A

boiling a kettle

108
Q

cathode is connected to which side

A

cathode to negative

109
Q

anode is connected to which side

A

anode to positive

110
Q

which loses mass the cathode or the anode?

A

copper anode loses mass

111
Q

which one gains mass the cathode or the anode?

A

copper cathode gains mass

112
Q

electrolysis

A

current causing a chemical reaction

113
Q

2 practical examples of electrolysis

A

ELECTROPLATING a less expensive metal with silver

RECHARGING your mobile phone battery

114
Q

what happens to a compass when current flows through it

A

turns 90º from original position

115
Q

experiment to verify joule’s law

time interval to allow water to heat up

A

3 minutes

116
Q

experiment to verify joule’s law

y -axis

A

temperature rise

117
Q

experiment to verify joule’s law

x-axis

A

current ²

118
Q

type of graph

A

straight-line graph through the origin

119
Q

joules law

A

P ∝ I ²

120
Q

experiment to verify joule’s law

2 points on accuracy

A

make sure the interval for which the current flows is fixed and the mass of the water is constant
check ammeter for zero error and correct if necessary

121
Q

showing that temperature rise ∝ I ² is equivalent to showing that

A

P ∝ I ²

122
Q

heat generated by electricity =

A

heat gain of water

123
Q

I ² R t =

A

m c Δ θ

124
Q

in the power station voltage is

A

x1000

125
Q

in the power station current is

A

÷1000

126
Q

what multiplies the voltage in the power station

A

a step-up transformer

127
Q

why is current ÷1000

A

to obey the conservation of energy

128
Q

heat generated in transmission cables is

A

÷ 1 000 000

129
Q

why is heat generated in transmission cables ÷ 1 000 000

A

joules law (Δθ ∝ I²)

130
Q

heat losses to the air reduced by a factor of

A

1 000 000

131
Q

what doe it mean that heat losses to the air reduced by a factor of 1 000 000

A

a huge reduction of energy losses and a huge saving in money terms

132
Q

brown wire

A

live wire

133
Q

blue wire

A

neutral wire

134
Q

green/yellow wire

A

earth wire

135
Q

ring circuit

A

current takes 2 paths from the fuse to the socket

136
Q

current along each path in ring circuit

A

half the current the appliance will use

137
Q

ring circuit, heat generated reduced

A

by a factor of 4

138
Q

what is the reduced risk of overheating in a ring circuit

A

a definite safety factor

139
Q

fuse

A

a protective device that cuts off the flow of current if the current is about exceed a certain value

140
Q

what does the fuse limit

A

limits the current that can flow in a circuit

141
Q

what does the fuse prevent

A

prevents a wire from overheating and therefore reduces the risk of a fire starting

142
Q

what does a fuse not do

A

does not prevent a person from being electrocuted

143
Q

mains voltage

A

230 V

144
Q

I =

A

P/V

145
Q

what fuse do you choose

A

with a current rating above the current you figure out with the closest value

146
Q

what appliances have an earth wire

A

appliances with metal on their outer surface

147
Q

what does an earth connection provide?

A

a good conducting path from the outer metal surface to the earth

148
Q

if the live wire accidentally came in contact with the outer metal surface of an appliance, what would happen?

A

flow through the earth rather than through a person who may be in contact with the appliance

149
Q

what does the earth connection protect?

A

protects the person from electric shock

150
Q

MCB

A

miniature circuit breaker

151
Q

what does the MCB do?

A

limits the current flowing in a circuit

152
Q

fuse blows, MCB …

A

trips

153
Q

when an MCB trips

A

can be reset by the flick of a switch

154
Q

if the current flowing in an electromagnet increases…

A

the magnet flux density is quite large

155
Q

what can increased magnetic flux density do

A

can be used to break the circuit by opening the switch

156
Q

RCD

A

residual current device

157
Q

current in live wire and neutral wire

A

should be the same

158
Q

if current in live and neutral are not the same

A

RCD wil be activated and current will stop immediately

159
Q

response of RCD

A

very fast

160
Q

what does the RDC offer?

A

great protection to a person against the dangers of electrocution

161
Q

bonding

A

if live wire touches any metal objects in the house the current will flow into the earth not a person touching them, protects from electrocution

162
Q

MEASURING THE RESISTIVITY OF A NICHROME WIRE:

one way to make a reading more accurate

A

use a more sensitive ohmmeter

163
Q

derive equation for resistors in series

A

Vt = V1 + V2 + V3
Rt It = R1I1 + R2I2 + R3I3
all I values are equal ->
Rt = R1 + R2 + R3

164
Q

derive formula for resistors in series

A 
Vt = V1 = V2 = V3
total current split in 3
It = I1 + I2 + I3
Vt/Rt = V1/R1 + V2/R2 + V3/R3 
all V values are the same
1 / Rt = 1/R1 + 1/R2 + 1/R3
165
Q

inert

A

unreactive

166
Q

Current voltage graph for: metals

A

straight line through the origin

167
Q

Current voltage graph for: filament bulb

A

curves up and across

168
Q

Current voltage graph for: ionic solution (active electrodes)

A

straight line through the origin

169
Q

Current voltage graph for: ionic solution (inert electrodes)

A

straight line a little bit to the right of the origin

170
Q

Current voltage graph for: gases

A

straight line through the origin, then horizontal, then diagonal again

171
Q

Current voltage graph for: vacuum

A

straight line through the origin, then horizontal

172
Q

Current voltage graph for: semiconductor

A

curves right and then up

173
Q

definition of semiconductor

A

a material with conductivity or resistivity between that of a conductor and an insulator

174
Q

intrinsic conduction

A

when a semiconductor material starts to conduct due to heating the material

175
Q

explain intrinsic conduction

A

as the temperature increases the atoms of silicone vibrate more vigorously, some of the bonds are broken, free electrons and positive holes now available to act as conductors

176
Q

for semiconductors; the higher the temperature

A

the greater the conduction

177
Q

LDR

A

light dependent resistor

as the intensity of light falling on it increases the level of conduction increases

178
Q

other name for extrinsic conduction

A

doping

179
Q

definition of extrinsic conduction

A

when the addition of a controlled quantity of an impurity increases conduction

180
Q

what do you add in n-type doping and why?

A

a group V element such as phosphorous as 5 outer electrons, 4 involved in bonding and 5th acts as a conductor

181
Q

majority charge carrier in n-type doping

A

the 5th outer electron in phosphorous

182
Q

why is it called n-type doping

A

the majority charge carrier is negative (electron)

183
Q

what is added in p-type doping and why?

A

a group III element such as boron is added, 3 outer electrons, creates a positive hole, available to act as a conductor

184
Q

majority charge carrier in p-type doping

A

the positive hole

185
Q

p-n junction 2 sides

A

a piece of silicon is p-type doped on the left and n-type doped on the right

186
Q

p-n junction what diffuses across the junction?

A

some free electrons from the n-type to the p-type and some positive holes from the p-type to the n-type

187
Q

p-n junction what happens to the 2 regions

A

n-type region loses electrons and becomes positively charged
p-type region gains electrons and becomes negatively charged

188
Q

p-n junction what happens once the 2 sides are charged

A

eventually these charged regions are sufficient to prevent further diffusion or charges, a potential barrier has been set up

189
Q

potential barrier

A

junction voltage

190
Q

junction voltage for silicon

A

0.6 V

191
Q

junction voltage for germanium

A

0.2V

192
Q

depletion layer

A

there are no charge carriers on either side of the junction and this area is called the depletion layer

193
Q

Pn junction is known as

A

diode

194
Q

how do you put a diode in reverse bias

A

negative terminal to the p-type junction

195
Q

putting a diode in reverse bias what reinforces the potential barrier

A

the external voltage

196
Q

putting a diode in reverse bias width of the depletion layer

A

increases

197
Q

putting a diode in reverse bias resistance

A

very high, the pn junction does not conduct

198
Q

a current will through diode in forward bias if

A

the current is significant enough for the voltage to exceed the junction voltage

Physics (11 decks)

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