1. Conduction of electricity Flashcards

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1
Q

Difference between vector and scalar?

A

Vector = magnitude and direction
Scalar = magnitude only

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2
Q

Define electric current (I)

A

A flow of charge

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3
Q

Define electric charge (Q)

A

current x time, measured on Coulombs

An electron has a charge of 1.6x10^-19C
(ofc in data booklet but mehhh, first principles)

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4
Q

Define coulomb (C)

A

1C = total charge supplied by a current of 1A in a time of 1s

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5
Q

Equation for number of electrons in a wire?

A

Total charge in circuit/Charge of an electron

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6
Q

Which direction is convectional current?

A

Positive (+) –> Negative (-)

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7
Q

But how do we know electron flow is negative –> positive?

A
  • Current is the flow of negative free electrons
  • Positive metal ions don’t move
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8
Q

What is drift velocity?

A

The average speed at which electrons travel in a conductor when subjected in an electric field

When a current is applied the electrons still move randomly but tend to move in one direction

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9
Q

How to derive drift velocity
step 1

A

From diagram of wire 3D shape:
- Gain area = A
- Gain drift velocity = V
- Gain time = t
- Gain number of free electrons = n

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10
Q

How to derive drift velocity
step 2

A

Gain length:
v x t = L

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11
Q

How to derive drift velocity
step 3

A

Gain volume:
A x L = Avt

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12
Q

How to derive drift velocity
step 4

A

Number of electrons:
nAvt

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13
Q

How to derive drift velocity
step 5

A

Gain total charge:
Q = nAvte

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14
Q

How to derive drift velocity
step 6

A

Re-arrange for current:
Q/t = nAve

Q/t = current O_o

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15
Q

How to derive drift velocity
step 7

A

Gain current:
I = nAve

Let it rest

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16
Q

Drift velocity in conductors? (metal)

A
  • Good
  • High electron density
17
Q

Drift velocity in insulators? (rubber, plastic)

A
  • Bad
  • Low electron density (1 free electron)
18
Q

Drift velocity in semiconductors? (silicon)

A
  • Varies
  • High electron dens. if temp high
  • Low electron dens. if temp low