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Nat 5 Physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

Definition of power?

A

the rate at which electrical energy is transferred to other forms

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2
Q

Explain how you would use an LDR, a variable resistor and a transistor to make a light switch on when the light level in a room drops.

A

The variable resistor and LDR are placed in series to create a potential divider circuit. In bright light, the resistance of the LDR is low, and therefore the p.d of the transistor is low so the transistor remains off. But, when the light level decreases, the transistor’s input p.d increases due to the fact that the resistance of the LDR increases. This causes the transistor to turn on, allowing current to flow to the lamp.

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3
Q

How can a circuit containing a transistor be used as a switch?

A

A circuit containing a transistor can be used as a switch because transistors turn on when their input p.d reaches a certain value and when this happens, the transistor allows current to flow to the rest of the circuit.

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4
Q

Explain how potential dividers can be used to run a component that requires a low p.d from a high p.d source.

A

potential dividers are two resistors which are placed in series in order to split voltage up based on each resistor’s respective resistance.

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5
Q

Why does adding more resistors in parallel make the total resistance of the circuit decrease?

A

because it causes an increase in current and as current goes up resistance goes down.

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6
Q

Where is an electric field created?

A

around any Electrically charged object

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7
Q

What happens to the electric field strength as you get closer to the charged object?

A

It gets stronger

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8
Q

What type of force does a charged object feel in another’s electric field?

A

Attraction or repulsion

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9
Q

What is the relationship between opposites and like charges?

A

Opposites attract, like charges repel

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10
Q

Where does the attraction/repulsion force come from?

A

due to the electric fields of each object interacting

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11
Q

How does distance affect the force between two charged objects?

A

Greater distance means weaker force

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12
Q

How can electric fields be shown in diagrams?

A

by drawing electric field lines

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13
Q

Where do electric field lines go from and to?

A

Positive to negative and are always drawn at a right angle to the surface of a charged object

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14
Q

What is the relationship between line closeness and field strength?

A

Closer lines indicate stronger field

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15
Q

Field lines show the direction that a force would act on a ——— charge placed at each point and the ——- charge would feel an opposite force.

A

positive
negative

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16
Q

What can field lines be used to evaluate?

A

the path that a charge would take if placed in the field.

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17
Q

What is electric current?

A

term which describes the electrical charge transferred per unit of time

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18
Q

What is needed for current to flow?

A

Source of potential difference

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19
Q

How is current measured?

A

Amperes (A)

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20
Q

Who is the electric current unit named after?

A

André-Marie Ampère

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21
Q

What are the charge carriers in metals?

A

Electrons

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22
Q

What is the conventional flow of current?

A

Positive to negative (old idea, incorrect) actually goes from -ve to +ve

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23
Q

What is a characteristic of a closed series circuit?

A

Current stays the same

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24
Q

What materials allow easier flow of electric charge?

A

Conductors

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25
Q

What are materials that do not allow electric charge flow called?

A

Insulators

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26
Q

What does resistance measure?

A

opposition to flow of current

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27
Q

What is the unit of resistance?

A

Ohms

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28
Q

What is the formula for Ohm’s law?

A

V=IR

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29
Q

How can you measure resistance?

A

Using ohmmeter or multimeter

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30
Q

What component allows changes to be done to current without using a variable supply?

A

Variable resistor

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31
Q

What is the relationship between potential difference and current in a circuit with a constant resistance?

A

the potential difference is directly proportional to the current

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32
Q

What are components which follow Ohm’s law known as? (when the resistance is constant and the p.d and current are directly proportional, then it follows ohm’s law)

A

Ohmic, (opposite is non-ohmic). a resistor with a constant temperature is ohmic.

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33
Q

What happens to resistance typically with temperature?

A

Increases

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34
Q

What causes a component to heat up?

A

because when an electrical charge has to flow, it does work against resistance, causing an electrical transfer of energy, some of which is turned into heat.

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35
Q

What happens to resistance as temperature increases?

A

It increases. when a component gets too hot, its resistance is so high that current can’t flow at all.

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36
Q

What is the behavior of thermistors with temperature?

A

Resistance decreases when temperature increases

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37
Q

Where must ammeters be placed?

A

In series

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38
Q

Where must voltmeters be placed?

A

In parallel

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39
Q

What verifies a resistor follows Ohm’s Law when drawing an I-V graph?

A

Straight line through origin (you can also calculate the resistance from the gradient)

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40
Q

How is resistance calculated for an ohmic conductor?

A

Gradient = 1/R (R should stay the same if the resistor is ohmic)

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41
Q

What I-V graphs do non-ohmic components have?

A

curved ones showing that the resistance isn’t fixed

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42
Q

What should be done to maintain ohmic conditions during experiments?

A

Use low currents, cool-downs between repeats

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43
Q

When do LEDs emit light?

A

when Current flows only in one direction

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44
Q

How do LEDs compare to other lighting types?

A

More efficient as they use much smaller currents

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45
Q

What do LEDs indicate in a circuit?

A

Presence of current

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46
Q

Where are LEDs commonly used?

A

Home appliances(often to show when turned on), digital clocks, traffic lights, remote controls.

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47
Q

What do photovoltaic cells do?

A

Transfer light into electrical energy

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48
Q

What can small solar cells (or photovoltaic cells)power?

A

Calculators

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49
Q

What can large solar cells power?

A

Entire satellites

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50
Q

What is a relay?

A

A switch using an electromagnet called a relay coil

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51
Q

What is an electromagnet?

A

a magnet which only becomes magnetic when an electric current is flowing through it

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52
Q

What do relays connect?

A

Two isolated circuits, so that when one is turned on, the other will too

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53
Q

Why are relays used?

A

To isolate low p.d from high p.d

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54
Q

What are the advantages of using relays?

A

Protects switch circuit and user

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55
Q

What is the purpose of a relay in a car’s starter motor?

A

To control high current safely and not allow it to get into bits where it is dangerous to have a high current, like where you turn your key

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56
Q

What happens when the switch in the low current circuit is closed?

A

Electromagnet activates and generates a magnetic field which then causes an attraction force to close the other switch

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57
Q

What happens in the high current circuit when the switch in the low current circuit is opened?

A

The electromagnet turns off and stops pulling causing the high current switch to open and the circuit breaks

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58
Q

What type of material is usually used in a relay?

A

Iron contacts

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59
Q

What do microphones do?

A

convert sound energy into electrical energy

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60
Q

What energy does a motor convert?

A

Electrical energy into the kinetic energy of a rotating coil, within the motor

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61
Q

What is a disadvantage of motors?

A

Waste energy as heat and sound

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62
Q

What happens if one component is removed in a series circuit?

A

Loop is broken, everything stops

63
Q

In series circuits, total voltage equals what?

A

Sum of all voltage at components

64
Q

How is voltage shared in series circuits?

A

Shared across components

65
Q

What is the current like in series circuits?

A

Same from every point

66
Q

How do you calculate total resistance in series?

A

Sum of respective resistances

67
Q

What happens when a resistor is added in series?

A

Voltage is shared, current lowers

68
Q

What happens to potential difference with higher resistance?

A

More potential difference

69
Q

What increases voltage in a series circuit?

A

More cells

70
Q

How are house electrics connected?

A

Parallel circuits

71
Q

What is used to connect all sockets in a building?

A

Ring main

72
Q

Benefit of a ring main?

A

Sockets can be turned on/off separately

73
Q

Voltage supply to sockets in a ring main?

A

Full 230V

74
Q

Connection type for components in parallel circuits?

A

Separately connected

75
Q

What happens if a component is disconnected in a parallel circuit?

A

Others are hardly affected

76
Q

What is the voltage like in parallel circuits?

A

Same everywhere

77
Q

What must be equal at the junctions of a parallel circuit?

A

Total current in = total current out

78
Q

How is current divided between two identical components in parallel?

A

Equally divide

79
Q

When do transistors automatically turn on?

A

When their input p.d. reaches a certain level

80
Q

What are transistors used in?

A

Street lights, things that turn on automatically

81
Q

Name two types of transistors.

A

Npn transistors and MOSFET transistors

82
Q

What are npn transistors also known as?

A

Bipolar transistors

83
Q

What are the parts of an npn transistor?

A

Base, collector, emitter

84
Q

What is the input voltage in an npn transistor?

A

Voltage between base and emitter

85
Q

What happens when the input voltage of a transistor reaches a certain value?

A

Transistor turns on

86
Q

What are the three terminals of a MOSFET transistor?

A

Gate, drain, source

87
Q

What is the input p.d in a MOSFET?

A

p.d between gate and source

88
Q

What happens when the input p.d of a MOSFET reaches a certain value?

A

Transistor turns on and the current will start flowing between the source and the drain

89
Q

What is electric current?

A

the electric charge transferred

90
Q

How does electric current flow in A.C circuits?

A

Electrons can flow either way

91
Q

Alternating Current

A

Direction changes constantly

92
Q

How can A.C circuits be created?

A

can be produced when alternating p.d.s are used which means the positive and negative ends of the p.d keep alternating

93
Q

Direct Current

A

Direction does not change

94
Q

Frequency

A

Times current changes direction

95
Q

What formula calculates the charge that has passed in a certain amount of time?

A

Q=It

96
Q

What is measured in coulombs?

A

Charge

97
Q

When drawing a circuit diagram in an exam, make sure to draw it with what?

A

wires have straight lines. needs to be fully closed (ignoring switches).

98
Q

What are the places where the circuit splits represented by?

A

black dots

99
Q

What is the driving force that pushes the charge round?

A

Voltage or potential difference

100
Q

What is one volt?

A

One joule per coulomb

101
Q

What is an LDR dependent on?

A

light intensity

102
Q

What is an LDR?

A

resistor that is dependant on light intensity

103
Q

What will the resistance fall in?

A

brightness

104
Q

What can LDRs be used for?

A

automatic night lights, outdoor lighting and burglar detectors

105
Q

What’s a thermistor? And what happens when it gets hot?

A

a temperature dependant resistor. Resistance lowers

106
Q

Thermistors can be used as temperature detectors in car engines and what type of electronic devices?

A

thermostats

107
Q

What is a diode and what is it typically made from?

A

A diode is a device which lets current flow freely but only in one direction as resistance is too high in the other direction. Semiconductors like silicon. They are often used in electronic circuits

108
Q

What happens when the capacitor is charged?

A

current stops flowing

109
Q

What is a capacitor?

A

a component which stores charge but they can only store small amounts

110
Q

What can capacitors be used to store charge in for a few seconds before releasing it instantaneously?

A

camera flashes

111
Q

How do you charge a capacitor?

A

by connecting them to a source of p.d. as current flows round the circuit, the charge gets stored in the capacitor.

112
Q

What happens to the current the longer you charge the capacitor?

A

it gets smaller

113
Q

What happens when the potential difference across the capacitor is equal to that of the battery?

A

current stops flowing and the capacitor is fully charged.

114
Q

The more charge being stored in the capacitor, the higher the —————- across it

A

potential difference

115
Q

What happens to the capacitor when you remove the battery?

A

it discharges and the current is the same for discharging as it is for charging but the current flows in the opposite direction.

116
Q

What are loudspeakers?

A

devices which transfer electrical energy into the vibration of a cone inside the loudspeaker, which creates sound waves

117
Q

What does a loudspeaker transfer into the vibration of a cone?

A

electrical energy

118
Q

What is electrical energy converted to in a microphone?

A

sound energy

119
Q

What do sound waves do in a microphone?

A

cause a diaphragm in the microphone to vibrate, then turning those vibrations into electrical signals.

120
Q

What is like a loudspeaker but in reverse?

A

Microphones

121
Q

What is the same for each resistor added in parallel?

A

the driving force that pushes current through the circuit

122
Q

What does this increase by adding another loop?

A

increases the total current

123
Q

What are potential dividers?

A

pairs of resistors

124
Q

What are pairs of resistors?

A

Potential dividers

125
Q

What do potential divider circuits do to get different outputs of voltage?

A

divide the p.d

126
Q

What is the frequency of D.C flowing in the same direction?

A

0 hertz

127
Q

What is an example of D.C?

A

batteries

128
Q

What is the UK’s main supply?

A

230V, A.C

129
Q

What is the frequency of the supply in the UK?

A

50 hertz per second

130
Q

What can supply direct current?

A

Cells and batteries

131
Q

What is a cathode ray oscilloscope (CRO)?

A

a type of voltmeter which can be used to get current traces on a screen

132
Q

What does the vertical height of an a.c trace on an oscilloscope show?

A

input voltage

133
Q

What type of trace does A.C show?

A

wave trace and the trace shows how the voltage of the supply changes with time

134
Q

What type of trace does D.C show?

A

straight line trace

135
Q

What is the p.d on a D.C trace on a CRO?

A

the distance from the straight line trace to the centre line

136
Q

Oscilloscopes can be connected to what in order to record the a.c and d.c traces?

A

data logging systems and the traces would look the same as those on the CRO

137
Q

What does energy transferred depend on?

A

power

138
Q

The power of an appliance is defined as what?

A

the amount of electrical energy transferred per second

139
Q

P=…

A

E/t

140
Q

What are appliances usually given?

A

a power rating

141
Q

What does a power rating do?

A

shows the maximum safe power that an appliance can work at. This can normally be assumed to be the appliance’s maximum operating power.

142
Q

What does power depend on?

A

on the p.d across the appliance and the current

143
Q

What do the p.d and current show in relation to power?

A

the voltage will tell you the amount of energy transferred by each unit of charge and the current will tell you how much charge passes over a unit time.

144
Q

How do you calculate the power of an appliance if you know the voltage and current?

A

P=IV

145
Q

What is electrical power measured in?

A

Watts

146
Q

Why are fuses used in appliances?

A

when appliances go above their power ratings they can cause fires

147
Q

As power gets higher, what happens to the current?

A

it gets higher too

148
Q

How do fuses work?

A

a fuse contains a strip of metal that will melt if current gets too high, causing the circuit to break, turning off the appliance and ensuring safety

149
Q

What are fuses always labelled with?

A

the current they melt at

150
Q

What must you remember when putting a fuse in an appliance?

A

put a fuse with a higher current than the maximum safe current of the appliance

151
Q

What two types of fuses are there usually?

A

3A and 13A

152
Q

If you don’t know the maximum safe current, use what rule to work out which fuse to use?

A

power rating<720W, use 3A.
power rating>720W, use 13A

153
Q

Describe an experiment in which Ohm’s Law can be verified.

A

A D.C supply is varied and readings are taken off of an ammeter and voltmeter before being graphed. When graphed in an I-V graph, the resistance of the component should equal the gradient of the graph if the component is Ohmic (follows Ohm’s Law)

Nat 5 Physics (2 decks)

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