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Physics A-level > Electricity > Flashcards

Electricity Flashcards

1
Q

Current is the measure…

A

of the amount of charge moving per second.

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2
Q

Current=

A

ΔQ/Δt

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3
Q

Electrons only…

A

drift in a random direction, so there is no net movement of charge.

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4
Q

When p.d. is applied across…

A

a conductor, a current is produced. This causes a movement of charge in one direction rather than a rapid flow.

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5
Q

Conventional current is…

A

historically from + to -

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6
Q

Electron flow is…

A

real flow from - to +

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7
Q

The electrical signal travels by…

A

electromagnetic waves, caused by the electrons.

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8
Q

A charge can be either…

A

positive or negative(ions).

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9
Q

Semiconductors:

A
  • the number of charges changes with temperature

- as the temperature increases, it liberates electrons so the resistance is reduced

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10
Q

Series circuit:

A
  • current is the same

- p.d. adds up

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11
Q

Parallel circuit:

A
  • the current adds up

- p.d. is the same

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12
Q

Best conductors are:

A

copper, silver and gold.

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13
Q

Best conductors have many…

A

conduction electrons(delocalsied)

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14
Q

Number density is…

A

the number of conductive electrons per unit volume. (n)

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15
Q

Mean drift velocity is…

A

mean velocity of an electron (3mm/s)

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16
Q

Current(with number density)=

A

nAvq (number density x A x mean drift velocity x charge of a carrier)

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17
Q

A charge of electrons =

A

number of electrons x electron charge

18
Q

A battery consists of…

A

many cells.

19
Q

A potential difference is a measure…

A

of energy provided to the charge carriers.

20
Q

V =

A

W(J) / Q(C)

21
Q

P.d. between A and B is…

A

the energy per unit charge as the charge moves from A to B.

22
Q

E.m.f. is…

A

electromotive force, which is the energy transferred by a source in driving unit charge around a complete circuit.

23
Q

In a battery, chemical…

A

energy is transferred to electrical energy.

24
Q

Resistance is a measure…

A

of the opposition, a material exerts against the flow of electrons.

25
Q

R=

A

V/I-current

26
Q

Resistance is measured in…

A

ohms.

27
Q

The Ohm is the resistance…

A

of a component when a p.d. of 1V drives a current of 1A through it.

28
Q

Resistance is caused by ions…

A

colliding with atoms.

29
Q

Ohm’s law states that current…

A

in an ohmic conductor is proportional to the voltage across it, when temp. and other physical conditions are kept the same.

30
Q

An ohmic conductor is a conductor…

A

that obeys Ohm’s law.

31
Q

Filament lamp graph:

A
  • for small voltages, the graph is roughly a straight line

- at a higher voltage, the line starts to curve, the gradient increases

32
Q

Why does the gradient in filament lamp increases with higher voltage?

A

Because, the temperature increases with higher current.

33
Q

Tresh-hold voltage is where…

A

the diode starts to conduct (0.6 V on average)

34
Q

A diode in a forward direction after passing…

A

tresh-hold point the resistance of diode decreases rapidly.

35
Q

A diode in reverse direction, the resistance…

A

is almost infinite so very little current.

36
Q

A diode in the breakdown stage, the current…

A

becomes infinite, the heating effect is very big and it is destroyed.

37
Q

Tresh-hold for LED is around…

A

2 V

38
Q

LDR is…

A

Light-dependent resistor. It is an input transducer. Resistance decreases as light intensity increases.

39
Q

Transducer is…

A

a device that transforms one physical quantity into another.

40
Q

The resistance of LDR can fall from…

A

1 M ohms in darkness to 500 ohms in the light.

41
Q

Thermistor is…

A

input transducer. Decreasing resistance with increasing temperature.

42
Q

NTC is…

A

negative temperature coefficient thermistor. The resistance decreases with increasing temperature.

Physics A-level (11 decks)

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