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AQA A-level Physics > Section 5 - Electricity > Flashcards

Section 5 - Electricity Flashcards

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1
Q

What is needed for current to flow?

A

Mobile charge carriers

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2
Q

What way does convetional current flow?

A

From positive to negative

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3
Q

Define current. Equation and words

A
  • I = ΔQ/Δt
  • Current is the rate of change of charge
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4
Q

What is an insulator?

A

Every electron is attatched to an atom

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5
Q

What is a conductor?

A

There are de-localised electrons

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6
Q

What is a semi-conductor?

A

The number fo charge carriers changes with a physical conditon

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7
Q

Define voltage. Equation and words

A
  • V = W/Q
  • Volatge is the workdone per unit charge
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8
Q

Define EMF

A
  • Electromotive force
  • The electrical energy produced per unit charge passing through a source
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9
Q

What are the 3 power eqautions?

A
  • P = IV
  • P = I²R
  • P = V²/R
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10
Q

What is the definiton of resistance? Equation and words.

A
  • R = V/I
  • Resistance is the ratio of Voltage across a compnent to the current through it.
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11
Q

How much resistance should an ideal Ammeter have and why?

A
  • It should have no or very low resistance
  • Because they are always connected in series and they should not affect the overall ciruit resistance
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12
Q

How much resistance should an ideal Voltmeter have and why?

A
  • It should have infinite resistance
  • Because if current flows through the voltmeter the voltage will be shared across the component and the voltmeter.
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13
Q

What is ohms law?

A

PD across and ohmic conductor is proportional to current through it provied the physical conditons don’t change

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14
Q

Define resistivity

A

A property of a material which gives a reference to the amount of resistance in a material

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15
Q

What is the resistivity equation?

A

R = ρ . L/A

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16
Q

What happens to resistance as the length of a material increases and why?

A
  • It goes up.
  • Because as length increases the amount of collisions wiht other electrons increases.
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17
Q

What happens to resistance as area increases?

A

It decreases becuase there is more spaces for more free electrons to flow without colliding

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18
Q

What is a super conductor?

A

A material that has no resistance when cooled below the critical temperature

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19
Q

What are some uses of superconductors?

A
  • Mag-lev trains
  • MRI scaners
  • Particle accelerators
  • Strong electromagnets
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20
Q

Draw a resistivity(Ω) vs temperature(K) graph for a superconductor

A

Check notes for graph

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21
Q

Draw the I / V graph for a wire (ohmic conductor)

A

Linear straight through origin

22
Q

Draw the I / V graph for a fillament lamp

A

s-shape

23
Q

Draw the I / V graph for a high temperature and low temperature graph on the same axes

A

check notes

24
Q

Draw the I / V graph for a diode

A
25
Q

Define threshold voltage

A

The minimum volatage needed to allow current to flow through a diode

26
Q

Draw the graph for an ntc

A

Check notes

27
Q

What happens to resistance in a PTC as temperature increases?

A

Resistance increases

28
Q

What happens to resistance in a NTC as temperature increases?

A

Resistance decreases

29
Q

What is Kirchoff’s first law?

A

the total current flowing into a junction is equal to the current
flowing out of that junction

30
Q

What is Kirchoff’s second law?

A

the sum of all the voltages in a series circuit is equal to the
battery voltage

31
Q

Formula for resistors in series?

A

R₁+R₂+R₃+…

32
Q

Formula for resistors in parallel?

A

1/R₁ + 1/R₂ + 1/R₃ + …

33
Q

What is the total current equal to in a parallel circuit?

A

The sum of the current in all the branches

34
Q

True or false the PD across in each branch in the same as the supply voltage?

A

True

35
Q

Formula for voltages in series

A

V₁+V₂+V₃ + …

36
Q

Formula for indentical voltages in parallel

A

V₁=V₂=V₃ = …

37
Q

For a series circuit the current is?

A

The same everywhere in the circuit

38
Q

For a series circuit the total volatage is equal to?

A

The supply voltage

39
Q

What is the rate of heat transfer equation?

A

I²R

40
Q

Define internal resistance

A

The resistance to the flow of charge within a source

41
Q

What is the emf formula?

A
  • ε = I(R+r)
  • ε = V(load) + V(int-resistance)
42
Q

What is the formual for power supplied by the cell?

A

I.ε =I²R + I²r

43
Q

What is terminal PD?

A

The voltage across the terminals of the battery

44
Q

What is the y-int and the gradient on an terminal pd vs I graph?

A
  • The y-int is the emf
  • The gradient is -r
45
Q

How is Y = mX + c realted to the emf formula?

A

V = -r.I + ε

Y = mX+c

46
Q

What is a potential divider?

A

A circuit with two or more resistors in parallel with a source of fixed PD

47
Q

What is the purpose of a potential divider?

A
  • To supply a fixed voltage between 0v and the supply voltage
  • To supply a variable PD
  • To supply a varibale PD that changes with physical conditions
48
Q

What is the potential divider formula?

A

V(out) = (V(supply) R₁ )
——————-
R₁+R₂

49
Q

What is an ohmic conductor?

A

A component with constant resistance

50
Q

The net motion of electrons are the cause of electric currents in metallic wires. What particles with charge that is greater than ±1e can also cause an electric current?

A

Ions

51
Q

How to find short circuit current on an internal resistance graph?

A

x intercept

52
Q

Typical voltage accross a led that is conducting?

A

1.8v

AQA A-level Physics (14 decks)

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