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Physics Unit 2 > Electricity > Flashcards

Electricity Flashcards

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1
Q

(Static Electricity) Why does negatively charged electrons get dumped onto the material and not positively charged protons ?

A

Only the electrons move- never the positive charges

both positive and negative charges are produced by the movement of electrons.

positive charge- when electrons move elsewhere

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2
Q

(Static Electricity) how do the materials repel/attract eachither

A

when two electrically charged objects are brought close together they exert a force on one another.

opposite electric charge = attract
same electrical charge= repel
Forces get weaker the further apart they get

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3
Q

How is a built up of static electricity caused

A

by friction.

  1. when some insulating materials are rubbed together, negatively charged electrons will be scraped off one and dumped on the other

so one will have a positive static charge and the one with dumped electrons will have a negative static charge.
The way the electrons are transferred depends on the materials

  1. These electrically charged objects will then attract small objects placed near them
    Eg polythene and acetate rods being rubbed by a cloth duster (rod becomes positive)
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4
Q

(Static) Do conductors make chargers hard or easy to travel through

A

electrical charges move easily through some materials, known as conductors

metals are good conductors

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5
Q

what does current mean

A

current is flow of electrical charge round the circuit. Unit= A ampere

it will only flow if there is a potential different across that component

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6
Q

What is potential difference

A

Potential difference is the driving force that pushes the current round (Unit: V) volts

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7
Q

what is resistance

A

resistance is anything that soles the flow down Unit: Ohm (horseshoe shape)

The greater the resistance across a component, the smaller the current that flows (for a potential difference across the compound)

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8
Q

how do you calculate the total charge through a circuit

A

CURRENT AND TIME

              charge             Q Current=---------   I  =-----
               time                 T

More charge passes around a circuit when a bigger current flows

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9
Q

how do you calculate the potential difference that passes through two points in an electrical circuit

A

potential difference across an electrical component is ther amount of energy transferred by that electrical unit per unit of charge

        work done                W P.D.= -------------   or    -----
        Charge                    V x Q
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10
Q

LEARN THE CIRCUIT SYMBOLS FOR

A 
a cell
a battery
a open switch
a closed switch
a filament lamp (bulb)
a fuse
a LED
a resistor
a variable resistor
an ammeter
a voltmeter
a diode
a LDR
a thermistor
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11
Q

What is the standard test circuit (learn what it looks like)

A

used for testing resistance of a components (by measuring current and potential difference) and for getting V-I graphs

the component, the ammeter and the variable resistance or are all in series (so they can be put in any order in the main circuit).
The voltmeter has to be put parallel around the component under test

  1. As you vary the variable resistor it alters the current flowing through the circuit
    This allows you to take several pairs of readings from the ammeter and voltmeter, which you can then plot on a VI graph and find the resistance
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12
Q

How do you measure the current

A

Ammeter measures the current in amos

it must be placed in series, and placed anywhere within the series

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13
Q

How do you measure the potential difference

A

Potential difference is measured using a voltmeter (in volts)

it must be placed in parallel around the component under test

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14
Q

What do VI graphs show

A

VI graphs show how the current varies as you change the potential difference

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15
Q

What are the three important Potential difference-Current Graphs

A

Different resistors- directly proportional to PD and different resistors have different slopes

Filament Lamp- As the tempreture of the filament increases the resistance increases (so like a s curve)

Diode- current will only flow through a diode in one direction. A diode has a very high resistance in the opposite direction

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16
Q

Why does resistance increase with tempreture

A
  1. when electrical charge flows through resistor some energy is transferred as heat so resistor gets hot
  2. this heat energy causes ions in the conductor the vibrate more so it’s more difficulty for charge carrying electrons to get through so the current can’t flow as easily and the resistance increases
  3. Most resistors have a limit to the amount of current that can flow. More current=increase in temperature= increase in resistance =current decreases again
  4. This is why the graph for the filament lamp levels off at high currents
17
Q

What is the equation for resistance, current and PD

A

Potential difference= current x resistance
V
—–
I x R

The steeper the graph the lower the resistance. If the graph curves it means the resistance is changing. In this case R can be found by taking a pair of bales from the graph and putting them into his equation

18
Q

What’s a diode

A

A diode is a special device made from a semiconductor material e.g. silicon

  1. used to regulate the potential difference in circuits
  2. lets current flow freely through it in one direction but not in the other where it has a very high resistance
19
Q

What are light-emitting diodes

A

Light emitting diode (LED) emits light when a current flows through it in a forward direction

LEDs are used for lighting as they use a much smaller current than other forms of lighting.

LEDS indicate the presence of a current in a circuit (to show TV appliances are switched on, traffic lights, digital clocks).

20
Q

What is a light-dependant resistor (LDR)

A
  1. LDR is a resistor dependant on the intensity of light
  2. in bright light resistance falls
  3. in darkness resistance is highest

used for automatic night lights, outdoor lighting and burglar detectors

21
Q

What is a thermistor

A

a thermistor is a temperature dependant resistor

  1. hot conditions resistance drops
  2. cool conditions resistance goes up
    make useful temperature detectors eg car engine temperature sensors and electronic thermostats
22
Q

what are the rules of series circuits

A
  1. if you remove one component the circuit is broken and they all stop
  2. potential difference is shared between the various components so all voltages around a circuit add up to equal the source voltage
  3. the same currents flows through all parts do the circuit A1=A2
  4. the total resistance is the sum of all the resistances, more resistance =higher PD
  5. the more cells connected the same way, the bigger the PD
23
Q

what are the rules of parallel circuits

A
  1. each component is separately connected to the +ve and -ve supply
  2. if a component is remove it hardly affects the others
  3. All components get the full source of PD, so voltage is same across all components
  4. Current through the battery is the same as the sum of the other currents in the branches A= A1 +A2…
  5. there are junctions where the current either splits or rejoins. total current going into junction=total current leaving
24
Q

What are the Voltmenters and ammeters exceptions to the rule

A

ammeters always connected in series - even in a parallel circuit

voltmeters always connected in parallel with a component- even in a series

25
Q

give a real life example of a series circuit

A

christmas lights

when one does out they all do

but the bulbs can be very small due i the total PD being shared out, so each bulb only had a small potential difference

26
Q

give a real life example of a parallel circuit

A

IN A CAR

parallel connection is essential to turn everything off and on separately and for everything to get full voltage from the battery

slight effect when you turn lots of things on lift may go dum because the battery can’t provide full voltage under heavy load

Physics Unit 2 (7 decks)

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