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Physics A level > Electricity > Flashcards

Electricity Flashcards

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1
Q

Define current

A
  • The rate of flow of charged particles
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2
Q

What is the equation for current?

A
  • I = ΔQ / Δt
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3
Q

What is the equation for Voltage?

A
  • V = W / Q
  • or
  • V = E / Q
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4
Q

Define Resistance

A
  • R = V / I
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5
Q

Define Voltage

A
  • One volt is one Joule per coulomb
  • It is what makes the current flow
  • V=W/Q
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6
Q

What is Ohms law?

A
  • Special case where current is directly proportional to voltage for constant temperature
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7
Q

What is the the ditribution of current a consequence of?

A
  • Conservation of charge
  • Total current into a junction = Total current out
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8
Q

What is the distribution of potential difference a consequence of?

A
  • Conservation of energy
  • Total emf from cells = Total p.d in circuit
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9
Q

Derive the equation for combining resistances in parallel

A
  1. IT = I1 + I2 (conservation of charge)
  2. VT / RT = V1 / R1 + V2 / R2
  3. 1 / RT = 1 / R1 + 1 / R2
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10
Q

Derive the equation for combining resistances in series

A
  1. VT = V1 + V2 (Conservation of energy)
  2. ITRT = I1R1 + I2R2 (I cancels as current is the same in series circuit)
  3. RT = R1 + R2
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11
Q

What are the seven base units?

A
  1. Second
  2. Metre
  3. Kilogram
  4. Amp
  5. Kelvin
  6. Mole
  7. Candela
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12
Q

What does V and I do in series?

A
  • V splits (Conservation of energy)
  • I is same (Conservation of charge)
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13
Q

What do V and I do in parallel

A
  • V is same across each branch (conservation of energy)
  • I splits between branches (conservation of charge)
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14
Q

What are the equations for power

A
  • P = IV
  • P = I2R and P = V2 / R
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15
Q

What is the resistivity equation?

A

R = pl / A

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16
Q

What is the equation which includes charge carrier density?

A
  • I = nAve or I = nAvq
17
Q

What is the difference between potential difference and potential

A
  • P.D is difference in potential between two points
  • Potential is joules per coulomb at a point
18
Q

Define emf

A
  • emf is the energy per coulomb converted into electrical energy by the cell
19
Q

Define internal resistance

A
  • Resistance in battery itself which causes lost volts as heat
20
Q

Define terminal p.d

A
  • Terminal p.d is the electrical energy converted per coulomb into other forms
21
Q

Define Resistivity

A
  • A constant for a given material at a given temperature
22
Q

What does emf stand for?

A
  • Electromotive force
23
Q

What are Thermistors and LDRs (in general)?

A
  • Semiconducters
  • They are resistors whose resistance is based on local conditions
24
Q

What is the rule for Thermistors for a negative thermal coefficient?

A
  • As temperature increases, resistance decreases
25
Q

Explain why when temperature increases in Thermistors, the resistance decreases?

A
  1. I = nAve
  2. As temperature increases, drift velocity decreases as there are more collisions between electrons and lattice. Amplitude of oscillations increases.
  3. But charge carrier density increases as more charge carriers are released hence why resistance decreases
26
Q

What is a use for Thermistors and LDRs?

A
  • Sensors
27
Q

What happens if you increase the light intensity at LDR?

A
  1. As more photons hit the LDR, more charge carriers are released
  2. This means charge carrier density increases, current increases and resistance decreases
28
Q

What is the ideal voltmeter?

A
  • Ideal voltmetere draws no current
  • Has ∞ resistance
29
Q

What is an ideal Ameter?

A
  • Ideal Ameter has no voltage drop
  • Resistance of 0
30
Q

What is the real resistance of an Ameter?

A
  • 0.5 Ohms
31
Q

What is real resistance of a voltmeter?

A
  • 50 mega Ohms
32
Q

What happens to the potential as you travel along a wire with no components?

A
  • It decreases linearly
33
Q

Draw a graph for distance along wire and potential difference?

A
34
Q

Learn this diagram on Potential Dividers!

A
35
Q

Equations for Energy?

A
  • E = IVt or W = IVt
  • E = Pt
36
Q

Core practical 2: Determine electrical resistivity

  • Independant
  • Dependant
  • Equation
  • y = mx + c
  • Graph to plot
A
  • Length
  • Resistance
  • R = pl / A
  • y = mx + c
  • y axis is R
  • x axis is l
  • m = resistivity/A
37
Q

Core practical 3: Determine emf and internal r of cell

  • Independant
  • Dependant
  • Equation
  • y = mx + c
  • Plot graph
A
  • Current
  • Terminal p.d
  • E = V + Ir
  • y = mx + c
  • y axis = V
  • x axis = I
  • m = r
  • y intercept = emf

Physics A level (11 decks)

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