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Physics GCSE > P4-electricity > Flashcards

P4-electricity Flashcards

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1
Q

What are conductors of electricity

A

Conductors of electricity are materials electrons flow easily through

E.g metals

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2
Q

What are insulators of electricity

A

Insulators of electricity are materials that electrons cant flow through

E.g cloth

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3
Q

What happens when two insulators are rubbed together

A
  • When two insulators are rubbed together electrons can pass from one to the other
  • The insulator that gains electrons becomes negativley charged, The insulator that loses electrons has an positive charge equal in size to the negative charge
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4
Q

What happens when a cloth is rubbed together with a plastic rod

A
  • The cloth is covered with electrons , the electrons cannot move through the cloth as it is an insulator
  • The plastic rod is also covered with electrons , the electrons cannot move through the rod as it is an insulator
  • When the plastic rod is rubbed together with the cloth electrons move from the rod to the cloth.The cloth has gained electrons so has a negative charge. The plastic rod has lost electrons so has a positive charge (which is equal in size to the negative charge on the cloth).
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5
Q

What happens when oppositley charged objects are placed near each other

A

When oppositley charged objects are placed near each other they are attracted to oacb other

The force between them is a force of attraction

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6
Q

What type of force is a force of attraction

A

A force of attraction is a non contact force

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7
Q

When happens when like charged objects are placed near each other

A

When like-charged objects are placed near each other they repel each other

-There is a force of repulsion between the two objects carrying the like charges

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8
Q

What will happen if a charged object is placed in the electric field of another charged object

A

If a charge object is placed in the electric field of another charged object, it will experience a force. This will be a force of replusion if the two objects are like charged and a force of attraction if the two objects are oppositley charged

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9
Q

What is an electric field

A

An electric field is a field of charge created around any charged object(see cgp if confused)

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10
Q

How do scientists show electric fields

A

Scientists show electric fields using field lines. Feild lines are perpendicular to the surface of the object

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11
Q

What do the arrows on the field line show

A

The arrows on the field lines show the direction of the force the other object feels if it is nearby (arrows facing inwards for force of attraction and outwards for force of repulsion )

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12
Q

What is the relationship between the distance of the field lines and the strength of the electric field

A

The closer the field lines are to each other the stronger the electric field is

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13
Q

What is the relationship between the distance between the TWO CHARGED OBJECTS and the force between them

A

If you decrease the distance between the two charged objects the force between them gets stronger (force of repulsion if two like charged objects or force of attraction if two oppositley charged objects)

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14
Q

Draw the circuit symbol for a cell

A

See CGP for answer

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15
Q

Draw the circuit symbol for a bulb

A

See CGP for answer

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16
Q

Draw the circuit symbol for an open switch and a closed switch

A

See CGP for answer

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17
Q

What is an electric current

A

An electric current is the flow of electrons round a circuit

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18
Q

What is electric current measured in

A

Electric current is measured in amperes (A) which can be shortened to amps

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19
Q

What is a series circuit

A

A series circuit is a circuit with no branches. In a series circuit the current can only flow in one direction

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20
Q

How do you measure the current in a circuit

A

You measure the current in a circuit using an ammeter

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21
Q

What is the current like all the way around a series circuit

A

The current in a series circuit is the same all the way around
E.g if you measure with an ammeter at any point it will read the same amount of amps

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22
Q

What direction does the current flow in a series circuit

A

The current flows from the negative end of the cell to the positive end (however scientists draw it in the opposite direction , this is called conventional current)

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23
Q

Draw the symbol for an ammeter

A

See CGP for answer

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24
Q

What happens in a closed circuit with a component

A

In a closed circuit with a component ,electrons first leave the cell . They carry energy from the cell to the components in the circuit and pass the energy on. They then return to the cell with less energy than they started with

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25
Q

What is a parralel circuit

A

A parralel circuit is a circuit that contains multiple branches-The current can flow through all of the branches

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26
Q

How is the current split between the different branches

A

The current in the branches adds up to the total current leaving the cell ( e.g if the total current was 0.7 amps and the current on one branch was 0.4 amps the current on the other branch would be 0.3 amps )

-A1+A2=Atotal

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27
Q

Why is a spark caused sometimes between oppositley charged objects

A
  • Normally, if two objects are oppositley charged, electrons in the air molecules between the two electric fields experience a force towards the positive object
  • If the field is too strong, sparking happens , because some of the electrons are pulled out of air molecules by the force of the field. This causes the air molecules to ionise which makes the air conductive which means a current can flow through the air molecules
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28
Q

What is potential difference

A
  • Potential difference is the driving force that pushes current round the circuit
  • Potential diffenerence between two points in an electrical circuit is the energy trabsferred per coulomb of charge that passes between the points
  • A potential difference of 1 volt tells us that one joule of energy is transferred for each coulomb of charge moving through the circuit
29
Q

Draw the symbol for a voltmeter

A

See CGP for answer

-NOTE: a voltmeter needs to be connected parralel to the circuit you are measuring the potential difference of

30
Q

What is the rule for potential difference in a series circuit

A

For a series circuit the total potential difference of the supply is shared between the components in the series( e.g if the potential difference of the supply was 9 volts and there were two components the potenetial difference of each of the components would be 4.5 volts )(if these two were lamps both the lamps would be dimmer as there is only half the volts)

31
Q

What is the rule for potential difference in a parrallel circuit

A
  • For compenents in parralel, the voltage remains the same for each component
  • The voltage is the same for all the banches
  • NOTE if two components are on the same branch in a parralel circuit the voltage still splits between them and it is the same total voltage as voltage of the supply( see photo off free science lessons)
32
Q

What is a battery

A

A battery is two or more cells connected together

33
Q

What is one key rule about batteries involving direction

A

The cells in a battery must be connected in the same direction (e.g positive ends must be on the same side )

34
Q

How does the potential difference of the cells in a battery link to the total potential difference of the battery*

A

The potential difference of individual cells in a battery adds up to give the total potential difference of the battery

E.g if there were 3 cells in a battery and each of them were 9 volts the total potential difference of the battery 27 volts (3x9)

35
Q

What happens one cell in the battery is placed the wrong direction *

A

If one cell in the battery is placed in the wrong direction the voltage of that cell is cancelled out from the total voltage if the battery

E.g if one cell in a three cell battery (each cell has 9 volts)is placed in the wrong direction the total voltage would be 18 (27-9)

36
Q

What unit is electrical charge measured in

A

Electrical charge is measured in coulombs

37
Q

What is the equation involving charge flow

A

Charge flow (Coulombs)(C)=Current(A)xTime(seconds)

Q=IxT

A current of 1 ampere = one couloumb of charge flowing per second

38
Q

What happens whenever charge flows in a circuit

A

Whenever charge flows in a circuit work is done/energy is transferred

39
Q

What is the equation that links energy transferred to electricty

A

Energy transferred(J) = charge flow (Coulombs)x potential difference (Volts)

40
Q

What is resistance

A

Resistance tells us the amount of potential difference required to drive a current through a component

41
Q

What is resistance measured in

A

Resistance is measured in ohms (♎️)

42
Q

What is the equation for resistance

A

Resistance (ohms )=potential difference(volts)/current (Amps)
Or
Potential difference (V) = current x resistance

If a component has a lower resistance less potential difference will be required to push the current through it

43
Q

What happens when electrons flow through a conductor

A

As electrons move through a conductor they collide with ions in the metal conductor and the electrical energy carried by them is transferred to other energy stores e.g thermal energy . This is what resistance is caused by

44
Q

Draw the symbol for a resistor

A

See CGP for answer

45
Q

What do resistors do in a circuit

A

Resistors add extra resistance to a circuit

46
Q

Why might you use a resistor

A

You might use a resistor in a series circuit to make a component such as a lamp dimmer. To do this you would add a resistor to the circuit. This would cause the potential difference in the circuit to be split between the resistor and the lamp. This means less electrical energy is transferred to the lamp so it gets dimmer

47
Q

What happens in an ohmic conductor

A

An ohmic conductor is a type of resistor where the current moving through the resistor is directly proportional to the potential difference across the resistor

48
Q

What type of resistance does this type of resistor have

A

This resistor has a constant resistance. The resistance does not change if we increase the current .

However the resistance in an ohmic conductor will only stay constant if the temperature remains constant

49
Q

How does a filament lamp work

A

A filament is a very tightly coiled wire . In a filament lamp the wire gets extremely hot when a current runs through it this causes it to glow and give out light

50
Q

What is the relationship between current and potential difference in a filament lamp

A

The current through a filament lamp is not directly proportional to the potential difference

  • This is because the restistance of the filament bulb increases asbthe temperature of the filament increases. As temperature increases the ions in the filament vibrate more which means collide more with the electrons in the electric current. This means less current can flow per unit of pd and there is more resistance to the current
  • SEE GRAPH IN PHOTOS AND MEMORISE
  • A filament lamp is not an ohmic conductor as as potential difference increases current no longer increases because resistance is increasing
51
Q

What is the symbol for a diode

A

See CGP for answer

52
Q

Which direction does a current flow through a diode

A
  • A current flows through a diode in one direction only
  • This is because a diode has a very high resistance in the reverse direction
  • Diodes are very useful for controlling the flow of currents in circuits
53
Q

Draw a diode current potential difference graph

A

See CGP for answer

54
Q

Draw the symbol for an LED

A

See CGP for answer

55
Q

What does an LED do ? Why is it useful ?

A

An LED emmits light when a current flows through it

LEDs are extremely energy efficient sources of light

56
Q

What is the rule about resistors in a series circuit

A

Resistors in series add together to give the total resistance

(E.g if there were two resistors of 5 ohms the total resistance would be 10 ohms)

-This is because the current has to pass through each individual resistor in turn , it cannot bypass any resistors

57
Q

What is the rule for resistors in a parralel circuit

A
  • The total resistance of two resistors in parralel is less than the resistance of the smallest individual resistor
  • This is because with a parralel circuit there is more than one route for the current to take so more total current will flow therefore reducing the reistance (R=V/I)
58
Q

Draw the symbol for a light dependent resistor

A

See CGP for answer

59
Q

In what conditions is the resistance of the LDR high ? In what conditions is the resistance of the LDR low

A
  • In dark conditions the resistance of the LDR is very high
  • In light conditions the resistance of the LDR is very low

LDR’s can be used for night lights

60
Q

Draw a light intensity -Resistance graph for a LDR

A

See Book for answer

61
Q

In what conditions will the resistance of the LDR be high

A

In bright light, the resistance of the LDR falls

In darkness, the resistance of the LDR is highest

62
Q

Draw the symbol for a thermistor

A

See CGP for answer

63
Q

How does the resistance of a thermistor change with temperature

A
  • The resistance of a thermistor decreases if the temperature increases
  • The resistance of the thermistor increases if the temperature drops

(They work in a similar way to LDRs with the potential difference being shared across them and a component)

64
Q

Draw a resistance temperature graph for a thermistor

A

See CGP for answer

65
Q

What can you use a thermistor for

A

You can use a thermistor for a car engine temperature sensor or an electronic thermostat

66
Q

Why does a spark form when two charged objects are placed near each other

A

When one object is charged, there is a potential differnce between the object and the other object. When the potential difference is high enough the electrons will jump across the gap and a spark will form

67
Q

Draw the symbol for a variable resistor

A

See CGP

68
Q

Describe a practical to measure I-V characteristsics

A
  1. Set up the curcuit ( batteries connected by wires to component, component in series with ammeter and variable resistor and in parralel to voltmeter)
    2) First use the voltmeter to measure the potential difference across the component(could be resistor, filament lamp or diode

3) then use the ammeter to measure the current through the component
Record these values in a table

4) Now adjust the variable resistor and record the readings on the ammeter and voltmeter. Do this several times to get a range of results
5) switch the direction of the battery. This means the direction of the potential difference has reversed both the voltmeter and ammeter should give negative values
6) continue taking several readings of p.d and current
7) plot an IV graph

Notes with resistor :Do not leave the circuit on for too long or the temperature of the resistor might increase ans the p.d will no longer be directly proportional to the current

Notes with diodes:with the diode in the circuit you need an extra resistor as the diodie will be easily damaged by a high current . The extra resistor will keep current low and prevent damage to a resistor. Because the current will be low a more sensitive ammeter is needed this is called a milliammeter

69
Q

What factors affect the resistance of a wire

A

Length of wire-if the wire is longer there are going to be more ions for the electrons to flow past so a greater resistance

Larger cross section-If the cross section of the wire is bigger there will also be more ions for the electrons to flow past so more resistance

Heat-If the ions have more energy they will vibrate more a create more resistance

-conductor-if the metal is a better conductor the ions will vibrate more a create more resitance

Physics GCSE (19 decks)

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