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Physics - Topic 3 - Electric Circuits > Charge, Current And Potential Difference & Resistance and Resistivity > Flashcards

Charge, Current And Potential Difference & Resistance and Resistivity Flashcards

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1
Q

What is current?

A

Rate of flow of charge

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2
Q

What is the direction of conventional current flow?

A

Flows from +’ve to -‘ve

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3
Q

What is the current equation (with Q and t)

A

I = Q/t

I - current
Q - charge
t - time

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4
Q

What is one coulomb defined as?

A

Defined as the the amount of charge that passes in 1 second when current is 1 ampere

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5
Q

What is the symbol for a coulomb?

A

C

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6
Q

How do you attach an ammeter to a circuit?

A

You attach it in series

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7
Q

What is Potential Difference defined as?

A

1 V is when you do 1 Joule of work moving 1 coulomb of charge through a component

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8
Q

What is the Potential Difference equation (with E & Q)

A

V = E/Q

V - Potential Difference
E - Energy transferred/work done
Q - Charge

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9
Q

How do you attach a Voltmeter to a circuit?

A

In parallel

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10
Q

What is the maximum value a voltmeter or ammeter can read called?

A

Full scale deflection

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11
Q

What are charge carriers in liquid and gases called?

A

Ion

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12
Q

In a circuit what are the flow of charges particles?

A

Charge carriers (free electrons)

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13
Q

Does a flow of positively charged particles produce a current?

A

Produces the same current as if it were negative but in the opposite direction

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14
Q

Ionic crystals are [……]

A

Insulators

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15
Q

Once a ionic Crystal is molten they […….] electricity

A

Conduct

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16
Q

What is the mean drift velocity?

A

Is the average velocity of the charge carriers

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17
Q

What is the current equation with drift velocity?

A

I = nqvA

I = electrical current (A)
n = number density of charge carriers (m-3)
q = charge in each carrier (C)
v = mean drift velocity (ms-1)
A = cross sectional area (m*2)
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18
Q

What is the charge of an electron?

A

-1.6 x 10*19

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19
Q

So what does current depend on?

A
  • Number of charge carriers
  • velocity of charge carriers
  • area of the median the current is travelling through
  • the amount of charge a carrier has
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20
Q

Different materials have different numbers of […..][…..]

A

Charge carriers

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21
Q

What are free electrons?

A

The electrons on the outer wheel of an atom.

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22
Q

Semiconductors have […….] charge carriers

A

Fewer

23
Q

What do the charge carriers in a semiconductor need to have in order to give the same current than a metal?

A

Have a greater drift velocity

24
Q

How many charge carriers would a perfect insulator have?

A

0 so there would be no current

25
Q

If you put a 1-[………][……] across an electrical component a 2-[…..] will flow.

A

1 - Potential Difference

2 - Current

26
Q

How much 1-[……..] you get for a particular p.d depend on the 2-[………] of the component

A

1 Current

2 Resistance

27
Q

What is the resistance equation with (V & I)

A

R = V/I

28
Q

Define resistance?

A

1 ohm is if a Potential Difference of 1V make a current of 1 A flow through it.

29
Q

What three things determine resistance?

A
  • Length
  • Area
  • Resistivity
30
Q

How does length affect resistance?

A

The longer the wire the more difficult it is to make current flow

31
Q

How does area affect resistance?

A

The wider the wire the easier it is to make a current flow

32
Q

How does resistivity determine resistance?

A
  • Depends on the material it is made from

- Temperature

33
Q

Define resistivity?

A

The resistance of a 1m length with a 1 m*2 cross sectional area

34
Q

What is resistivity measured in?

A

Ohm meters (Ωm)

35
Q

What is the resistivity equation?

A

R = pl/A

R - Resisitance
p - Resistivity
l - Length (Meters)
A - cross sectional area (m*2)

36
Q

How do you know if you have gone way off when calculating resistivity?!

A

Typical values of resistivity conductors are really small.

But if you get 1 x 10-7 go back and check you’ve converted area into m2

37
Q

What is the resistivity of a material related to?

A
  • Number density of charge carriers ( and their mean drift velocity which varies with temperature)
  • the higher the current the lower the resistance
  • therefore the lower the materials resistivity
38
Q

For a [……][…….] R is constant on a P.D (X axis) Current (y axis) graph

A

Ohmic conductor

39
Q

What are conductors that obey Ohm’s Law called?

A

Ohmic conductors

40
Q

What is Ohm’s Law?

A

Provided the temperature is constant, the current through an ohmic conductor is directly proportional to the Potential Difference across it ( I ∝ V )

41
Q

For an Ohmic Conductor what does doubling the p.d do to the current?

A

Doubles it too!

42
Q

Finding the Resistivity of Wire - what do you need to find out first about the wire before finding out the resistivity?

A

Resistance

43
Q

Finding the Resistivity of Wire - What is the first measurement we take?

A

Cross sectional area of a wire (we assume that the wire is cylindrical so the wire is circular)
Using the equation AREA = πr*2

44
Q

Finding the Resistivity of Wire - What instrument do you use to find the diameter of the wire?

A

Micrometer

45
Q

Finding the Resistivity of Wire - Wen finding the diameter of the wire how many measurements do you take along the wire?

A

3 measurements at different points along the wire

46
Q

What is micrometer also called?

A

Micrometer caliper

47
Q

Finding the Resistivity of Wire - What is step 1?

A

Clamp the test wire to a ruler connected ruler to the circuit at the point where the ruler reads 0

48
Q

Finding the Resistivity of Wire - What is step 2?

A

Attached the flying lead to the test wire

49
Q

Finding the Resistivity of Wire - What is step 3?

A

Record the leg the of the test wire connected and the voltmeter reading and the ammeter reading

50
Q

Finding the Resistivity of Wire - What is step 4?

A

Use the readings on the voltmeter and the ammeter to calculate the resistance - R = V/I

51
Q

Finding the Resistivity of Wire - What is step 5?

A

Repeat the experiment for several different lengths within a sensible range

52
Q

Finding the Resistivity of Wire - What is step 6?

A

PLOT A GRAPH - of resistance against length and draw a line of best fit

53
Q

When calculating the resistivity of wire experiment, on the graph of resistance against length what does the gradient of the line equal?

A

Gradient is R/I = p/A

- So multiply the gradient of the line of best fit by the Cross Sectional Area to find the resistivity of the wire!

54
Q

Finding the Resistivity of Wire - What could cause results to be inaccurate?

A

Resistivity depends on TEMPERATURE!

Physics - Topic 3 - Electric Circuits (7 decks)

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