gcse physics > electricity > Flashcards

electricity Flashcards

(46 cards)

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1
Q

key equations (5)

A
  1. Q=IT
  2. V=IR
  3. E=QV
  4. P=IV
  5. P=E/T
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2
Q

what is current?

A
  • rate of flow of charge
  • measure by ammeter in amps
  • only flows around a complete circuit with a source of potential difference
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3
Q

equation linking current and charge

A

Q=It
(charge = current x time)
(coulombs, C = amps, A x s)

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4
Q

what is potential difference?

A
  • energy transferred per unit charge
  • measured by voltmeter in volts
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5
Q

what is resistance?

A
  • anything that opposes the flow of charge
  • measured by an ohmeter in ohms Ω
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6
Q

draw circuit diagram symbols for a variable resistor

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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7
Q

draw circuit diagram symbol for a cell

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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8
Q

draw circuit diagram symbol for a battery

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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9
Q

draw circuit diagram symbol for a fuse

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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10
Q

draw circuit diagram symbol for a thermistor

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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11
Q

draw circuit diagram symbol for a diode

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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12
Q

draw circuit diagram symbol for a LDR

A

check https://www.bbc.co.uk/bitesize/guides/zgvq4qt/revision/1

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13
Q

rules of series circuits (3)

A
  1. current is the same everywhere
  2. the potential difference is shared between the components
  3. the more the components, the higher the resistance
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14
Q

rules of parallel circuits (3)

A
  1. the potential difference is the same across each branch
  2. the p.d. is split between the components within the branch
  3. the current in each branch splits from the power supply (not always evenly)
  4. the more the components, the lower the resistance
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15
Q

what are measuring devices?

A

ideal meters

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16
Q

what is an ideal ammeter?

A
  • has 0 resistance
  • no energy is used up as the current flows through them
    (important as they are used in series)
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17
Q

what is an ideal voltmeter?

A
  • have infinite resistance
  • no current can flow through
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18
Q

what are potential dividers?

A

use of two or more resistors in series to ‘split’ the potential difference between them in the ratio of the resistance

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19
Q

what is the total resistance in series?

Study These Flashcards
A

the total resistance is simply the sum of the components

20
Q

equation for total resistance in series

21
Q

equation of total resistance in parallel

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A

1/R =1/R1 +1/R2

22
Q

what happens in an LDR as light intensity increases?

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A

resistance decreases since more photons hit the LDR, so more electrons released (so as light intensity increase, resistance decreases)

23
Q

how does temperature affect the resistance of a thermistor?

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A

as temp increases, resistance decreases because the ions in the thermistor vibrate more more releasing extra electrons, therefore reducing resistance

24
Q

what is an ohmic conductor and what is its resistance?

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A

components with constant resistance (doesn’t change with current) eg wires/ fixed resistors

25
what is an I-V characteristic and what does it show?
graph which shows how the current flowing through a component changes as the potential difference flowing across it is increased
26
describe the experiment to find a component's I-V characteristics eg filament lamp, resistor, diode
1. set up a series circuit with a battery, variable resistor, the component and ammeter 2. add a voltmeter parallel to the component 3. change the resistance of the variable resistor and record ammeter and voltmeter readings 4. swap over the wires so the direction of the current is reversed (get -ve values) and repeat 3 5. plot a graph of current (y-axis) to voltage (x-axis)
27
ohmic conductor i-v characteristics and why?
- linear graph trough the origin / - current through an ohmic conductor is directly proportional to the potential difference
28
filament lamp i-v characteristics and why?
- similar to a +ve cubic graph through origin - as the current increases, temp of filament increases, so resistance increases - this means less current can flow, so the graph gets shallower
29
diode i-v characteristics and why?
- flat on -ve side, steep curve on +ve side - current will own flow through the diode in one direction (very high resistance in other direction)
30
what is a fuse/ how does it work?
- will melt and break the circuit if current is too high - protects the user
31
3 types of wire and colours
1. neutral wire - blue 2. live wire - brown 3. earth wire - green and yellow stripes
32
what are the two types of electricity supplies?
- alternating current (ac) - direct current (dc)
33
what happens with an alternating current?
current is constantly changing direction due to alternating voltages in which the positive and negative ends keep alternating
34
what type of current is uk mains supply? (+ voltage and frequency)
- alternating current - 50 Hz - 230V
35
what supplies direct current?
cells and batteries
36
what happens in direct current?
current always flowed in same direction due to a direct voltage
37
what does the neutral (blue) wire do?
- completes the circuit - when the applaince is working normally, current flows through live and neutral wires - 0V
38
what does the live (brown) wire do?
provides the alternating potential difference at about 230V from the mains supply
39
what does the earth (green and yellow stripey) wire do?
- protection for wiring and user - stops the applaince from becoming live - provides a very low resistance route into the ground (since resistance is low the current is high, so the fuse melts and breaks the circuit) - 0V
40
why can you get an electric shock from a live wire?
- your body is 0V so if you touch a live wire (around 230V), a potential difference of 230V is produced across your body and a current flows through you because your body provides a link to the ground - this would cause a large electric shock which could injure or kill
41
what causes static electricity?
- friction rubs off insulators' electrons - one insulator will gain electrons so become negatively charged, whilst the other will lose electrons becoming positvely charged - charges are not free to move in an insulator so they build up in one place making is electrically charged
42
how can static electricity lead to sparks?
- as an electric charge builds up on an object, the potential difference of the object and earth increases - if the potential difference is large enough, electrons can jump across the gap between the charged object and earth/ any earthed conductor
43
why does a balloon that has been rubbed stick to the wall?
- STATIC ELECTRICITY - rubbed insulator (friction) causes electrons to be gained from the surface (becomes negatively charged) - the electrons in the wall are repelled, so the wall becomes positively charged so attracts the balloon
44
why does the balloon that has been stuck to the wall eventually fall off?
positively charged wall gains electrons from air molecules so no longer attracts balloon
45
what is an electric field?
- a field of attraction/repulsion created around any electrically charged object - the closer you are to the object, the stronger the field is
46
3 rules for drawing field lines
1. electric field lines ALWAYS go from positive to negative 2. the closer together the lines are, the stronger the field is 3. field lines are always drawn perpendicular to the surface
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