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physics alevel (theory) > Mod 4: charge and current > Flashcards

Mod 4: charge and current Flashcards

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1
Q

What equation shows the net charge on a particle

A

Q= +- ne. Where n is the number of electrons added or removed

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2
Q

What is the structure of a metal

A

A lattice of positive ions surrounded by delocalised electrons

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3
Q

How does solid metal conduct electricity

A

(Structure) one side of the metal is made to be positive and the other is made to be negative so the electrons will be attracted to the positive so current will flow through the structure

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4
Q

How does NaCl solution conduct electricity

A

The electrolyte NaCl contains +ve and -ve ions therefore the electrolyte will split into Na+ cations and Cl- anions so when a pair of electrodes are place in the solution the cations will be attracted to the cathode and the anions will be attracted to the anode. This produces an electrical current

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5
Q

Which is the +ve and _ve electrode

A

Anode= positive
Cathode= negative

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6
Q

What is conventional current

A

The flow of positive charge that moves in the opposite direction of electrons (+ve- -ve)

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7
Q

Describe the electron flow in a metal

A

It is in the opposite direction of conventional current

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8
Q

What is Kirchohoff’s first law

A

For any point in an electrical circuit the sum of the currents in to that point is equal to the sum of currents out of that point. This law is a consequence of conservation of charge as charge can not be created or destroyed.

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9
Q

What is mean drift velocity

A

The average rate of change of displacement of the charge carriers in a substance

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10
Q

Why does mean drift velocity happen

A

When e- move through a metal they frequently collide with the positive metal ions resulting in the random movement.

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11
Q

What does the number density n represent

A

The number of charge carriers per unit m^3

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12
Q

Describe the number density n in conductors vs insulators

A
  • the value n is much higher in conductors than in insulators therefore the e- in insulators must travel faster in order to carry the same current than the n in conductors
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13
Q

What does the V stand for in the equation
I=neV/dt

A

V=volume

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14
Q

What is the volume of a wire equal

A

The cross sectional area of the wire A x by its length

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15
Q

What is the time taken for the e- to cross the wire equal to

A

The mean drift velocity

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16
Q

How do we find the number n using an equation

A

N = Q/ e. ( E = elementary charge)

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17
Q

What is the net charge on a particle a multiple of

A

It is the multiple of e (elementary charge)

18
Q

How was the conventional current defined as

A

A flow of positive charge

19
Q

What is n the number density

A

The number of charge carriers per m^3

20
Q

What is drift velocity

A

The average rate of change of displacement of the charge carriers in a substance

21
Q

How do electrons travel

A

-ve to +ve

22
Q

A vertical transmitter aerial emits an em wave to a reactive that has a diode in its circuit. Explain why this is necessary for the receiver aerial to receive info

A

The current induced by the aerial is alternating so the diode rectifies this so info can be transmitted

23
Q

Which electrical quantity has the s.i unit of amperes per second

A

Charge

24
Q

What is elementary charge

A

The smallest unit that charge come in.

25
Q

What is the specific word to describe charge as a multiple of e

A

Quantised

26
Q

How many volts does 1JC^-1 equal to

A

1 V

27
Q

What is the energy transferred to a charged particle that is accelerated by a p.d equal to

A

The work done on the particle
: W=VQ.

W=Ve

28
Q

What is the unit for n in I=AneV

A

Metre^-3

29
Q

What is the n in perfect insulators and real insulators

A

0
Real insulators have very few n

30
Q

Is ionic crystals a conductor or an insulator

A

Insulator however once molten the liquid will conduct

31
Q

Describe an electrolyte

A

A substance that contains ions and conducts electricity when molten

32
Q

How may a gas become a conductor

A

When u apply a high enough voltage electrons will get ripped out of atoms making a spark, and giving u ions along a path

33
Q

What is the shape of the graph of the power of a fixed resistor that changes with current and why

A

Power is directly proportional to current squared therefore the graph will be a quadratic

34
Q

The lowest value at which an led lights up is 0.5V explain why this means ther is minimum energy transferred to the led

A

Because the minimum amount of p.d was supplied for current to flow through the diode and transfer energy

35
Q

Explain why the power dissipated by an LED in the forward direction is much less than the reverse direction

A

The resistance of the diode in the reverse direction is much greater and
P= V^2 / R
Therefore power is much lower in that direction as power is inversely proportional to resistance

36
Q

What is the is base unit for energy

A

Kgm^2s^-2

37
Q

Why does the light intensity increase in an LDR when the resistance decreases

A

Because the number density of charge carriers increases

38
Q

What quantity is conserved in Kirchhoff law 1st

A

Charge

39
Q

Define a coulomb

A

The charge which passes a point when a current of 1 amp flows for one second

40
Q

State the difference between the direction of conventional current and the charge flow in a metal wire

A

Charge flow in a metal is in the opposite direction of conventional current however in a metal electrons flow

41
Q

Describe mean drift velocity and the motion of electrons in a wire

A

The distance travelled along the wire each second, the electrons move in randomly but they all still drift towards the positive terminal

42
Q
A

physics alevel (theory) (20 decks)

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