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physics > Electricity > Flashcards

Electricity Flashcards

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1
Q

What is current ?

A

Rate of flow of charge in coulombs per second

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2
Q

What is the formula for charge current and time ?

A

Q = IT

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3
Q

What is the difference between electron flow and conventional current ?

A

conventional current is what is normally shown in Q’s where current flows away from positive and towards negative, electron flow is the opposite.

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4
Q

What is Ohm’s Law ?

A

The current flowing through a metallic conductor is directly proportional to the potential difference applied across it at a constant temperature.

V=IR

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5
Q

What is the charge of one electron ?

A

-1.6x10^-19

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6
Q

What is the definition of potential difference ?

A

PD between two points is the amount of energy transferred when one coulomb of charge passes through

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7
Q

What is the formula for work done ?

A

W = QV

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8
Q

What is the formula for power ?

A

W = PT
P = IV

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9
Q

What does a current voltage graph look like for a diode ?

A

current only allowed through one direction and is flat then increases

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10
Q

What does a current voltage graph look like for a fixed resistor ?

A

Linear through origin

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11
Q

What does a current voltage graph look like for a filament lamp ?

A

Linear through origin but then plateaus

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12
Q

WHat does it mean when a component is ohmic ?

A

Ohms law applies.

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13
Q

What is a potentiometer circuit ?

A

When a component is in parallel with a variable resistor which can be moved to change current through the component can be seen as component in parallel with a resistor then series with another.

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14
Q

What are the rules for a parallel circuit ?

A

Current is split between branches and PD is same everywhere

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15
Q

WHat are the rules of a series circuit ?

A

Current is the same everywhere and PD is split amongst components

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16
Q

What is Kirchoffs first law ?

A

At any junction in a circuit the sum of the current flowing into the junction is equal to the sum of the current flowing away from it

17
Q

What is Kirchoffs second law ?

A

In any complete loop of a circuit the sum of PD is equal to PD of the scource

18
Q

What is the formula for resistors in parallel ?

A

(1/r1 +1/r2 …)^-1

19
Q

What is the formula for resistors in series ?

A

r1 + r2 ….

20
Q

What is the relationship between resistors in a series circuit ?

And how would you work out PD across each resistor ?

A

resistor with largest resistance will have the largest PD vice versa. This is because current is equal everywhere but resistance is different so PD across each resistor is different

V(resistor) = R(resistor)/R(total) x V(total)

21
Q

What is a NTC thermistor ?

A

As temp increases resistance decreases

22
Q

What is a PTC resistor ?

A

As temp increases resistance increases

23
Q

What is a LDR ?

A

As light intensity increases resistance decreases

24
Q

What is the resistivity of a metal ?

A

How resistive the metal is in ohms per metre

25
Q

What is the formula for resistivity ?

A

R = ρ x L/A

26
Q

How do you work out the voltage across branches ?

A

On each side of voltmeter do one value take away the other
(see p29 electricity booklet for clarity)

27
Q

What is a superconductor and what are its uses ?

A

a type of material that conducts electricity with zero energy loss or resistance when cooled to its critical temperature

maglev trains

28
Q

What is the emf of a cell ?

A

Work done per unit charge on the whole circuit by the power source

29
Q

What is the TPD of a cell ?

A

Voltage across terminals when current is passing through

30
Q

WHy is TPD lower than the emf ?

A

Battery has internal resistance which can be shown as a resistor in series with the cell. This “resistor” uses x volts when current is flowing through working against the battery therefore it is lower

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