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AS Physics > Section 6 - Electricity > Flashcards

Section 6 - Electricity Flashcards

1
Q

Define current

A

The rate of flow of charge

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2
Q

Which direction does conventional current flow?

A

positive to negative

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3
Q

Define a coulomb

A

The amount of charge that passes in 1 second when the current = 1A

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4
Q

Define potential difference

A

Work done per unit charge moved

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5
Q

What is the potential difference across components connected in parallel

A

The same

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6
Q

Define a volt

A

When you convert 1J of energy moving 1 coulomb of charge through the component

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7
Q

Define Ohm’s law

A

The current across an ohmic conductor is directly proportional to the potential difference when the physical conditions are kept constant

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8
Q

What do I/V graphs show?

A

How resistance varies

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9
Q

What does the I/V graph for an ohmic conductor look like

A

Straight line through the origin

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10
Q

I/V graph: What would a low resistance and high resistance look like on the graph?

A

Straight steep line for low resistance

Straight shallow line for high resistance

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11
Q

What is the I/V graph for a filament lamp?

A

A curve that starts steep but gets shallower, and passes through the origin

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12
Q

What is a filament lamp?

A

A coiled up length of metal wire

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13
Q

When does the resistance of a metal increase?

A

When the temperature increases

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14
Q

Why aren’t semi conductors as good as conducting as metals?

A

Far fewer charge carriers

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15
Q

What happens when you supply energy to a semi conductor?

A

Charge carriers are released

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16
Q

Why do semiconductors make good sensors?

A

Because when energy is supplied, more charge carriers can be released

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17
Q

What happens as temperature increases in a thermistor?

A

Resistance decreases

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18
Q

What does the resistance/temperature graph look like for a thermistor?

A

Top left to bottom right curve

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19
Q

What does the I/V graph look like for a thermistor?

A

bottom left upward curve to origin, top right downward curve from origin

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20
Q

What happens as the voltage increases in a thermistor?

A

Current increases

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21
Q

What happens to a thermistor as current increases?

A

It heats up, and resistance decreases -> graph curves upwards as more current can flow

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22
Q

Why does heating up a thermistor reduce resistance?

A

Gives electrons enough energy to escape from atoms -> more charge carriers

23
Q

What do diodes do?

A

Only let current flow in one direction

24
Q

What is forward bias on a diode?

A

The direction in which the current is allowed to flow

25
Q

What is the threshold voltage on most diodes?

A

0.6V in the forward direction

26
Q

Explain what happens when the diode is in reverse direction

A

Resistance is very high, so a tiny amount of current can flow

27
Q

What things determine resistance?

A

Length, area, resistivity

28
Q

How does length effect resistance?

A

Longer the wire, more difficult it is for current to flow

29
Q

How does area effect resistance?

A

Wider the wire, easier it is for current to flow

30
Q

How does resistivity effect resistance?

A

Depends on material and structure. Generally depends on temperature and light intensity

31
Q

Define resistivity

A

The resistance of a 1m length with a 1m^2 area

32
Q

What are superconductors?

A

Materials with 0 resistance

33
Q

How do you lower the resistivity of many materials?

A

Cooling them down

34
Q

How do you make a material a superconductor?

A

Cool them down below the transition temperature and their resistivity disappears entirely. ONLY WORKS WITH CERTAIN MATERIALS e.g mercury

35
Q

What happens when a material has no resistance?

A

No electrical energy is turned into heat, so you can use a magnetic field to flow current

36
Q

What’s the down side of superconductors?

A

Most normal conductors have transition temperatures at 10K (-263C) - difficult to do and expensive

37
Q

What are applications of superconductors?

A

Power cables, strong electromagnets - Maglev trains, electric circuits work really fast

38
Q

Define power

A

The rate of transfer of energy

39
Q

How can you calculate the energy if you know the power and the time?

A

E=Pt

40
Q

How can you calculate the energy if you know the power?

A

E=IVt

41
Q

Where does resistance come from?

A

Electrons colliding with atoms and losing energy

42
Q

What type of energy makes electrons move?

A

Chemical energy

43
Q

Why must batteries have resistance?

A

Otherwise there wouldn’t be any atoms for electrons to collide with

44
Q

What is the resistance inside the battery called?

A

Internal resistance

45
Q

Define e.m.f

A

The amount of electrical energy the battery produces for each coulomb of charge

46
Q

What is the potential difference across the load resistance?

A

Energy transferred when 1 coulomb of charge flows through the load resistance

47
Q

What are lost volts?

A

Energy wasted per coulomb overcoming the internal resistance

48
Q

How do you calculate the e.m.f of cells in a series circuit?

A

Etotal = e1 + e2 + e3

49
Q

How do you calculate the e.m.f of cells in a parallel circuit?

A

Etotal = e1 = e2 = e3

50
Q

What’s the easiest way to measure e.m.f of a power supply?

A

Connecting a high resistance voltmeter across its terminals

51
Q

What happens to charge in a circuit?

A

It is conserved

52
Q

How do you calculate total I, V and R in a series circuit

A

I = I1 = I2 = I3, V = V1 + V2 + V3, R = R1 + R2 + R3

53
Q

How do you calculate total I, V and R in a parallel circuit

A

I = I1 + I2 + I3, V = V1 + V2 + V3, 1/R = 1/R1 + 1/R2 + 1/R3

54
Q

`NEED TO DO P86,87

A

LOL

AS Physics (12 decks)

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