Chapter 8 Charge and Current Flashcards

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1
Q

What is the unit for current?

A

Amperes

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2
Q

What is the definition for current and what is the equation?

A

It is the number of coulombs of charge per second passing a point
I = ΔQ / ΔT

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3
Q

What is electric charge?

A

It is a physical property and comes in two forms, positive and negative

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4
Q

What is the measure of electric charge? and what is the quantity of 1 coulomb

A

Coulombs

1 coulomb is the amount of charge that passes in 1 second when there is a current of 1 amp

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5
Q

What is the charge of an electron? and a proton?

A

Electron: -1.6x10^-19 Coulombs
Proton: 1.6x10^-19 coulombs

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6
Q

How do you calculate the charge on ions?

A

Take the relative charges (e.g. +1 or -2 etc) and multiply by 1.6x10^-19 to get the charge in coulombs

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7
Q

How is the charge on an object calculated?

A

Using the equation: Q = ±ne
Q = Charge
n = number of electrons added or removed
e = the elementary charge

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8
Q

What is the elementary charge and why is it elementary?

A

It is the smallest possible charge that something can have. It is the same as the charge of an electron, 1.6x10^-19
This is possible because charge is quantised

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9
Q

Explain charge quantisation

A

It means that the charge has fixed values which are integers of e where e is the elementary charge.
You cannot have any value of charge.

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10
Q

What are charge carriers and what are some examples

A

Charge carriers are anything that carries a charge. Examples include electrons or ions. When current flows through a liquid, the charge carriers are often ions in the liquid

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11
Q

What is the structure of a metal?

A

It is a regular crystalline structure of positive ions surrounded by a sea of delocalised electrons.

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12
Q

How does current flow through a metal?

A

When a metal is connected to different ends of a battery the free electrons move through the metal towards the positive end of the battery. NOT ALL ELECTRONS MOVE ONLY THE FREE ONES

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13
Q

What causes a large current?

A

More electrons moving through the wire at the same time

Electrons moving faster through the wire

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14
Q

What is the direction of conventional current vs electron flow

A

Conventional current flows positive to negative and electron flow is from negative to positive

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15
Q

What are electrolytes?

A

They are solutions that conduct electricity. They have ions that act as charge carriers that move through the solution and transfer charge

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16
Q

When conduction through an electrolyte what is the:

a) anode
b) cathode

A

a) anode is the positively charged end

b) cathode is the negatively charged end

17
Q

What happens to the positive ions in an electrolyte solution

A

The positive ions move towards the cathode and gain an electron. The negative ions move towards the anode and lose an electron.

18
Q

How is electric current measured?

A

Using an ammeter, it is placed in series in the circuit. It should have the lowest possible resistance.

19
Q

What is the law of the conservation of charge

A

Electric charge cannot be created or destroyed and so the total electric charge in the universe is constant

20
Q

What is Kirchhoff’s first law? what is the equation?

A

The sum of the currents into a point (junction) is equal to the sum of the currents out of that point
ΣI in = ΣI out

21
Q

What is the number density?

A

It is the number of free charge carriers per unit volume

22
Q

What is the number density of:

a) conductors?
b) semiconductors?
c) insulators?

A

a) Larger than 10^28 m^-3
b) around 10^17 m^-3
c) Small

23
Q

What is the problem with using semiconductors to transfer electricity?

A

The electrons have to move faster so the semiconductor heats up more

24
Q

How fast do charge carriers move? and why do lights turn on instantly

A

They move slowely but they all move at once so the light turns on instantly

25
Q

What is the equation for mean drift velocity?

A
I = Anev
I = Current
A = Cross sectional area
e = The elementary charge
v = mean drift velocity
26
Q

What is the mean drift velocity?

A

This is the mean speed of charge carriers

27
Q

What is the affect of changing the cross sectional area on mean drift velocity?

A

The smaller the cross sectional area the faster the electrons move in order for the current to be the same as a wire with a larger cross sectional area because there is less space for the electrons to pass.