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BMAT > Physics - Electricity > Flashcards

Physics - Electricity Flashcards

(70 cards)

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1
Q

what is an electrostatic conductor

A

material that is able to disperse electrical current (electrons) easily

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2
Q

what is an electrostatic insulator

A

do not disperse electrical charge (electrons) easily

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3
Q

what happens when two electrostatic insulators are rubbed together

A

there is a flow of charge from one insulator to another
insulator that loses electrons becomes positively charged
insulator that gains electrons becomes negatively charged

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4
Q

induction

A

place a neutral object next to charged object causes it to become charged
if one end of this newly charged object is momentarily earthed, the object becomes permanently charged

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5
Q

what happens is a newly charged object is momentarily earthed

A

becomes permanently charged

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6
Q

example of static electricity in industry

A

spray paint
paint droplets have opposite charges to the object being painted meaning they are attracted to the object and less paint is wasted

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7
Q

why can static electricity be dangerous

A

sparks can form upon spontaneous dissipation of electrical charge which can lead to a fire

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8
Q

what can reduce the risk of a spark

A

earthing an object

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9
Q

what are the two ways current can be supplied

A

direct
alternating

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10
Q

direct current

A

current always supplied in same direction

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11
Q

examples of uses of direct current

A

batteries or cells supply

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12
Q

alternating current

A

current that repeatedly changes direction

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13
Q

examples of uses of alternating current

A

power stations output and the mains

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14
Q

what is a waveform

A

current changes at certain regular frequency which produces a waveform

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15
Q

what is the frequency of mains current in UK and Europe

A

50Hz
50 oscillations or 100 changes in direction per second

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16
Q

what is current

A

flow of charged particles through an electrical conductor

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17
Q

what symbol represents current

A

I

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18
Q

what is current measured in

A

amperes (A)

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19
Q

how to calculate current

A

current = charge / time

current = amperes (A)
charge = coulomb (C)
time = second (s)

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20
Q

how to measure current

A

ammeter placed in series with components of series

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21
Q

what is potential difference (voltage)

A

work done to move charge between two points

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22
Q

what symbol represents voltage

A

V

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23
Q

what is voltage measured in

A

volts (V)

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24
Q

how to calculate voltage

A

voltage = work done / charge

voltage = volts (V)
work done = joules (J)
charge = coulomb (C)

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25
how to measure voltage
voltmeter which is always placed in parallel with the component whose potential difference you are trying to measure
26
what is resistance
opposition to the flow of current (electrons) through a conductor all conductors carry a certain resistance which is directly proportional to the length of the conductor and inversely proportional to the cross sectional area
27
what symbol represents resistance
R
28
what units are used for resistance
ohms (Ω)
29
how to calculate resistance
resistance = voltage / current resistance = ohms (Ω) voltage = volts (V) current = amperes (A)
30
what is 1 ampere
1 coulomb of charge flows through a conductor per second
31
what is 1 volt
work done moving 1 coulomb of charge between two points
32
what is 1 ohm
resistance of a conductor when a potential difference of 1 volt produces a current of 1 ampere
33
voltage-current graphs are linked by which equation
voltage = current x resistance
34
how is a voltage-current graph plotted
current on y axis voltage on x axis
35
what is an ohmic conductor
a fixed resistor maintains constant resistance with different currents flowing through it
36
ohmic conductors what is current and voltage relationship
directly proportional
37
how to calculate resistance on voltage-current graph
1/gradient
38
what are non-ohmic conductors
resistance alters with varying current flowing through them and varying potential differences across them
39
non-ohmic conductors what is current and voltage relationship
sigmoidal curve
40
example of non-ohmic conductor
filament lamp
41
why is filament lamp non-ohmic
as more current flows through filament lamp, it begins to heat up due to increased electron collisions heat generated leads to an increased resistance through filament lamp as particles vibrate with greater amplitude, making it harder for the free electrons to flow through the conductor this leads to a decrease in current
42
thermistors
thermistors are components whose resistance is dependent on temperature
43
example of thermistor
negative coefficient (NTC) thermistor's resistance decreases as its temperature increases
44
light dependent resistors
components whose resistance is dependent on light intensity incident on it resistance of LDR decreases as light intensity increases
45
ideal diodes
components that only allow current to flow in one direction which is shown by the arrowhead in the circuit symbol for the diode
46
what can diodes require before current flows through them sometimes
forward junction potential
47
what is a diode's breakdown voltage
in the reverse direction causes negative current to flow through them
48
series circuit
components placed on one long continuous path and current flows through every component
49
current in a series circuit
it is the same no matter where in the circuit it is measured from
50
potential difference in a series circuit
equal to the sum of potential difference across each of the components that the series circuit contains this is because the energy carried by each coulomb of charge must be shared as it travels through each component VT = V1 + V2 + V3
51
resistance in series circuit
sum of all components in a circuit RT = R1 + R2 + R3
52
how to calculate the voltage in a cell or battery in series
VT = RT x IT
53
what is a parallel circuit
components are arranged in several 'parallel' branches (can be in a series of series and parallel)
54
potential difference in parallel circuit
same across each loop in a parallel circuit due to the fact that the electrons entering each loop have the same amount of energy the total voltage supplied by the cell is equal to the voltage across each of the loops in the parallel circuit VT = V1 = V2 = V3
55
current in parallel circuit
shared between branches in ratio of resistance od components in each branch therefore, at a branch point the current will be equal to the sum of the currents going into each branch IT = I1 + I2 + I3
56
resistance in parallel circuit
reciprocal law 1/RT = 1/R1 + 1/R2 + 1/R3 dealing with circuits that consist of a combination of series and parallel resistors, use the reciprocal rule to calculate the total resistance of the parallel portion before adding the series resistances
57
electrical power equation
power = energy / time power in watts (W) energy in joules (J) time in seconds (s)
58
transfer of electrical power equation (using V and I)
power = voltage x current power in watts (W) voltage in volts (V) current in amperes (A)
59
transfer of electrical power equation (using I and R)
power = current^2 x resistance power in watts (W) current in amperes (A) resistance in ohms (Ω)
60
transfer of electrical power equation (using V and R)
power = voltage^2 / resistance power in watts (W) voltage in volts (V) resistance in ohms (Ω)
61
energy equation (using V I and T)
energy = voltage x current x time energy in joules (J) voltage in volts (V) current in amperes (A) time in seconds (s)
62
what do transformers do
devices that have the ability to alter voltage and current
63
what do step up transformers do
increase voltage and decrease current useful when transferring electricity from power stations to national grid in order to reduce energy losses
64
what do step down transformers do
decrease voltage and increase current more safe use in our homes and reduces risk of electric shocks
65
what does a transformer consist of and why
primary coil wrapped around coil when a current is allowed to flow through the primary coil, it creates a magnetic current which induces a current in a secondary coil
66
current and voltage can then be altered by varying the ratio of turns in the primary and secondary coils
(v in secondary coil / v in primary coil) = (turns on secondary coil / turns on primary coil)
67
power calculation using primary voltage and primary current
power = primary voltage x primary current
68
power calculation using secondary voltage and secondary current
power = secondary voltage x secondary current
69
generator effect
generation of a current by the movement of an electrical conductor relative to a magnetic field also : keeping stationary conductor in a fluctuating magnetic field
70
what does a generator consist of and why
wire rotating in a magnetic field - as it rotates each side of the coil moves through the magnetic field in two different directions withe each 360 degree rotation - wire simultaneously moving in opposite direction through the magnetic field, produces alternating current

BMAT (33 decks)

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