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AQA A Level Physics(Option A: Astrophysics) > Electricity > Flashcards

Electricity Flashcards

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1
Q

Define current

A

Net flow of charged particles per unit time

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2
Q

Define potential difference

A
  • Energy transferred per unit charge when electrical energy is converted into another form of energy
  • 1V = 1 J/C
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3
Q

Define resistance

A

A materials opposition to the flow of electric current

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4
Q

Define Ohm’s Law

A

For a given material, voltage is directly proportional to current at a constant temperature

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5
Q

What are I-V characteristics?

A

Graph showing how current flowing through a component changes with increasing voltage

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6
Q

Describe the I-V characteristics graph for an ohmic conductor

A

Straight constant gradient

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7
Q

Describe the I-V characteristics graph for a filament lamp

A
  • Bottom left is increasing curved gradient
  • Top right has decreasing curved gradient
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8
Q

Describe the I-V characteristics graph for a diode

A
  • Far end of negative p.d has very low negative current
  • Current doesn’t go above 0 until V > 0.6
  • After 0.6V, gradient curves upward steeply
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9
Q

Define resistivity

A

A property of a material that determines the resistance of a piece of given dimensions

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10
Q

What is units for resistivity?

A

Ωm / ohm metres

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11
Q

What are semiconductors?

A
  • A group of materials which conduct electricity, but not as good as metals
  • When temperature rises, they can release more carriers and their resistance decreases
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12
Q

State 3 common semiconductor components

A
  • Thermistors
  • Diodes
  • Light dependent resistors(LDR)
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13
Q

What is a thermistor?

A
  • A component with a resistance that changes with temperature
  • Resistance decreases as temperature increases
  • Temperature is normally controlled using a water bath
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14
Q

What is a LDR?

A
  • A component with a resistance that changes with light intensity
  • Resistance decreases as light intensity increases
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15
Q

What is a superconductor?

A

A material that has zero resistivity and zero resistance when cooled below a critical temperature

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16
Q

State 3 uses of superconductors

A
  • Power cables that transmit electricity without power loss
  • Really strong electromagnets with applications such as Maglev trains
  • Electronic circuits that work really fast with minimal energy loss due to having no resistance to slow current down
17
Q

Define power

A

Energy transferred per second in Watts

18
Q

What is the equation for Energy involving power?

A

E = Pt

19
Q

Define internal resistance

A

The resistance of the materials within the battery

20
Q

How does internal resistance occur?

A

Electrons in the chemical reactions collide with the atoms in the battery, losing energy which causes resistance

21
Q

Define electromotive force, emf

A
  • Energy transferred from chemical to electrical energy in a power system
  • Electrical energy per unit charge, in volts
22
Q

Define terminal p.d

A
  • Energy transferred from electrical energy to another type
  • Work done per unit charge, in volts
23
Q

For a V-I graph, what does the y-intercept represent?

A

emf

24
Q

For a V-I graph, what does the gradient represent?

A

Negative internal resistance

25
Q

State Kirchoff’s first law and the principle it’s based on

A
  • Sum of the currents entering a circuit = Sum of the currents leaving the circuit
  • Conservation of charge
26
Q

State Kirchoff’s second law and the principle it’s based on

A
  • Sum of the EMFs around a circuit loop = Sum of the PDs around that loop
  • Conservation of energy
27
Q

What is constant in a series circuit?

A

Current

28
Q

What is constant in a parallel circuit?

A

Voltage

29
Q

How do you find the total emf of cells in a series circuit?

A

ϵ(total) = ϵ1 + ϵ2 + ϵ3

30
Q

How do you find the total emf of cells in a parallel circuit?

A
  • ϵ(total) = ϵ1 = ϵ2
  • When cells are identical
31
Q

What is a potential divider?

A
  • A circuit containing a voltage source and a pair of resistors
  • The voltage across one resistor is used as an output voltage
  • If resistors aren’t fixed, the circuit will be capable of producing a variable output voltage
32
Q

State the relationship between resistance and length

A

Resistance is proportional to length

33
Q

State the relationship between resistance and cross-sectional area

A

Resistance is inversely proportional to cross-sectional area

34
Q

State the relationship between temperature and resistance for a metal conductor

A

As temperature increases, resistance increases

35
Q

Describe the relationship between temperature and resistance for a metal conductor

A
  • Resistance increases as temperature increases
  • As fixed ions of the metal gain energy and vibrate
  • This causes charge carriers to collide more, making them slow down
  • Therefore current decreases, which increases resistance
36
Q

State the equation for the output voltage of a potential divider?

A

V(out) = R(2) x V(in)/ R(1) + R(2)

AQA A Level Physics(Option A: Astrophysics) (15 decks)

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