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Science Spec Flaschcards > P2 > Flashcards

P2 Flashcards

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1
Q

What are in circuits?

A
  • Switches (open or closed)
  • Cell
  • Battery
  • Diode
  • Resistor
  • Variable resistor
  • LED
  • Lamp
  • Fuse
  • Voltmeter
  • Ammeter
  • Thermistor
  • LDR

(NOTE see page 179 for how they look as symbols)

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2
Q

What is needed for an electrical charge to flow through a closed circuit?

A

The circuit must include a source of potential difference

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3
Q

What is electric current?

A

Electric current is a flow of electrical charge

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4
Q

When will an electric charge only flow?

A
  • Electrical charge will only flow round a complete (closed) circuit if there is a potential difference
  • So a current can only flow if there’s a source of potential difference
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5
Q

What is the unit of current?

A

The unit of current is the ampere, A

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6
Q

What is the equation for charge flow?

A

Charge flow (C) = Current (A) x Time (s)

Q = It

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7
Q

No matter what, what does a current always have?

A

The same value at any point in a single closed loop

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8
Q

What does the current depend on?

A
  • The current (1) through a component depends on both the resistance (R) of the component and the potential difference (V) across the component
  • The greater the resistance of the component the smaller the current for a given potential difference (p) across the component
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9
Q

State the equation for potential difference

A

Potential difference (V) = Current(A) x Resistance(Ω)

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10
Q

Practical 15:

A
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11
Q

Give three examples for resistors

A
  • Ohmic conductor
  • Filament lamp
  • Diode
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12
Q

State how the ohmic resistors work

A
  • The resistance of ohmic conductors (e.g. a wire or a resistor) doesn’t change with the current
  • At a constant temperature, the current flowing through an ohmic conductor is directly proportional to the potential difference across it
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13
Q

State how the filament lamps work

A
  • When an electrical charge flows through a filament lamp, it transfers some energy to the thermal energy store of the filament, which is designed to heat up
  • Resistance increases with temperature, so as the current increases, the filament lamp heats up more and the resistance increases
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14
Q

State how diode works

A
  • For diodes, the resistance depends on the direction of the current
  • They will happily let current flow in one direction, but have a very high resistance if it is reversed
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15
Q

Out of ohmic conductors,filament lamps and diodes which ones have a constant resistance and which change

A

Stay constant : Ohmic conductors

Change : Diode and filament lamp

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16
Q

From the graph of ohmic conductor, what can you see

A

The current through an ohmic conductor (at a constant temperature) is directly proportional to the potential difference so you get a straight line

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17
Q

From the graph of filament lamp, what can you see?

A
  • As the current increases, the temperature of the filament increases, so the resistance increases
  • This means that the less current can flow per unit PD,so the graph get shallower - hence the curve
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18
Q

From the graph of diode, what can you see?

A
  • Call Roni flow for a diode in one direction, as shown
  • The diode has a very high resistance in the reverse direction
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19
Q

Why does the resistance of a thermistor decrease?

A

Because the temperature decreases

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20
Q

What is required in a circuit?

A

The applications of thermistors e.g a thermostat

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21
Q

Why does the resistance of an LDR decrease?

A

Because the light intensity increases

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22
Q

Note:

A

The application of LDRs in circuits, e.g. switching lights on when it gets dark as required

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23
Q

What is an LDR

A

A resistor that is dependent on the intensity of light

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24
Q

What is the use and design of a circuit?

A
  • To measure the resistance of a component by measuring the current through, and potential difference across, the component
  • The circuit is shown in a diagram with symbols
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25
Q

Note:

A

AQA may ask to draw a circuit diagram using correct circuit symbols

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26
Q

Note:

A

AQA says that students should be able to use graphs to explore whether circuit elements are linear or nonlinear, and relate the curves produced to their function of properties

27
Q

What are the two ways of joining electrical components

A

Series and in parallel, though some circuits include both series and parallel parts

28
Q

Characteristics for components connected in series circuits

A
  • There is the same current through each component
  • The total potential difference of the power supply is shared between the components
  • The total resistance of two components is the sum of the resistance of each component
29
Q

How do you find the resistance in series circuits?

A

R (total) = R1 = R2

30
Q

Characteristics for components connected in parallel circuits

A
  • The potential difference across each component is the same
  • The total current through the whole circuit is the sum of the currents through the separate components
  • The total resistance of two resistors is less than the resistance of the smallest individual resistor
31
Q

Note:

A

Check page 183 and 184 and memorise what the diagram for series and parallel circuits are

32
Q

Differences between series and parallel circuits

A

Find answer and put here

33
Q

Why does the resistance increase in a series circuit when adding resistors?

A
  • In a series circuit, adding resistors will increase resistance
  • The current is the same in every single component in the circuit, so the more resistors we add, the harder it is for current to flow
  • This means that the overall resistance has increased in a series circuit
34
Q

Why does the resistance decrease in a parallel circuit when adding resistors?

A
  • In a parallel circuit, the net resistance decreases as more components are added, because there are more paths for the current to pass through
  • The two resistors have the same potential difference across them
  • The current through them will be different if they have different resistances
35
Q

What is a DC series circuit?

A
  • When all the resistive components of a DC circuit are connected end to end to form a single path for flowing current
  • The manner of connecting components end to end is known as a series connection
36
Q

What are DC series circuits used for?

A

DC power is widely used in low voltage applications such as charging batteries, automotive applications, aircraft applications and other low voltage, low current applications

37
Q

Why are DC series circuits used for measurement and testing purposes

A

Unknown

38
Q

What is the equation for potential difference?

A

Potential difference(V) = Current(A) x Resistance(Ω)

39
Q

What is meant by equivalent resistance?

A

If a single resistance can replace the combination of resistances in such a manner that the current in the circuit remains unchanged, then that single resistance is called the equivalent resistance

40
Q

Note:

A

AQA wants students to solve problems for circuits which include resistors in series using the concept of equivalent resistance

41
Q

What is an example of an AC supply in the UK and what does the Domestic electricity supply have a frequency of and how much voltage does it have? (NOTE:)

A

Mains electricity is an AC supply in the United Kingdom. Domestic electricity supply has a frequency of 50 Hz and is about 230 V

42
Q

What is Direct potential difference?

A
  • A direct potential difference, also known as a DC potential difference, is a constant potential difference that always flows in the same direction.
  • This type of potential difference is produced by direct current (DC) sources, such as batteries
43
Q

What is alternating potential difference?

A
  • An alternating potential difference, also known as an AC potential difference, is a potential difference that changes direction regularly
  • This type of potential difference is produced by alternating current (AC) sources, such as power stations
44
Q

Most electrical appliances are connected to the mains using three-core cable,the insulation covering each wire is colour coded for easy identification, what are they?

A

Live wire - Brown
Neutral wire - Blue
Earth wire - Green and yellow stripes

45
Q

Characteristics of the live wire

A

The live wire provides the alternating potential difference (at about 230 V) from the mains supply

46
Q

Characteristics of the neutral wire

A

The neutral wire completes the circuit - when the appliance is operating normally, current flows through the live and neutral wires. It is around O

47
Q

Characteristics of the Earth wire

A
  • It is for protecting the wiring, and for safety - it stops the appliance casing from becoming live
  • It doesn’t usually carry a current - only when there’s a fault.
  • It’s also at 0 V
48
Q

Why is the live wire dangerous?

A
  • The live wire causes shocks
  • Since the live wire has a very large potential difference compared to the human body, the live wire can cause shocks
  • When you touch a live wire, current flows through your body and causes an electric shock
  • Open circuits are still dangerous
49
Q

Why is it dangerous to provide a connection with the live wire and earth wire?

A
  • Any connection between live and earth can be dangerous
  • If the link creates a low resistance bath to earth, a huge current will flow, which could result in a fire
50
Q

What are the two equations for power?

A

Power(W) = Potential difference(V) x Current(A)
P = VI

Power(W) = Current^2(A) x Resistance(Ω)

51
Q

What are electrical appliances designed to do?

A

Transfer energy to components in the circuit when a current flows

52
Q

What does the amount of energy an appliance transfers depend on?

A
  • How long the appliance is switched on for
  • The power of the appliance
53
Q

State examples of how kettles transfer energy

A

Kettles transfer energy electrically from the mains ac supply to the thermal energy store of the heating element inside the kettle

54
Q

State examples of how batteries transfer energy

A

Energy is transferred electrically from the battery of a handheld fan to the kinetic energy store of the fan’s motor

55
Q

When is work done in a circuit?

A

When charge flows

56
Q

State the equations for energy transferred

A

Energy transferred(J) = Power(W) x Time(s)
E = Pt

Energy transferred = Charge flow(C) x potential difference(V)

57
Q

How are current and potential difference related to power?

A
  • Current and potential difference are related to power in that power is equal to the product of current and potential difference
  • The more current flowing through a circuit, and the greater the potential difference, the more power is transferred
58
Q

How are current and potential difference related to the energy transferred?

A

The greater the power, the greater the energy transferred

59
Q

What is the power rating?

A
  • The power rating tells you the maximum amount of energy transferred between stores per second when the appliance is in use
  • Appliances are often given a power rating - they’re labelled with the maximum safe power that they can operate at
  • You can usually take this to be their maximum operating power
60
Q

Why does a higher power not truly not matter?

A
  • A higher power doesn’t necessarily mean that it transfers more energy usefully
  • An appliance may be more powerful than another, but less efficient, meaning that it might still only transfer the same amount of energy (or even less) to useful stores
61
Q

What is the national grid?

A
  • The national grid is a giant system of cables and transformers that covers the UK and connects power stations to consumers (anyone who is using electricity)
  • The national grid transfers electrical power from power stations anywhere on the grid (the supply) to anywhere else on the grid where it’s needed (the demand) - e.g. homes and industry
62
Q

What are step-up transformers used for?

A
  • Step up transformers are used to increase the potential difference from the power station to the transmission cable than step down
  • Transformers are used to decrease too much lower value,The potential difference for domestic use
63
Q

Why is the national grid an efficient way to transfer energy?

A
  • The transfer of electrical energy via the grid is very efficient
  • When currents in a cable are higher, more energy is dissipated to the surroundings through heating
  • As high currents waste more energy than low currents, electrical power is transported around the grid at a high voltage and a low current
64
Q

What is the equation for…

A

Potential difference across primary coil x current in primary coil = potential difference across secondary cool x current in secondary coil

(As in equation sheet)

Science Spec Flaschcards (24 decks)

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