Chapter 3 Flashcards

1
Q

A flow of charged particles produces an [ ]

A

Electric current

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2
Q

Each electron has the same [ ] measured in [ ]

A

Charge (Q)

Coulombs (C)

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3
Q

What equation links I, Q and t?

A

I = ΔQ/Δt

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4
Q

Current is measured in [ ]

A

Amperes (A)

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5
Q

The [ ] is the same at all points along the stream of [ ]

A

current

charged particles

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6
Q

Describe current when a wire forks

A

The current splits

I = I₁+I₂

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7
Q

What is Kirchhoff’s first law?

A

That the current at a junction must add up

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8
Q

When will charges move?

A

When attracted by charges of the opposite sign or when repelled by charges of the same sign

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9
Q

What happens inside a battery cell?

A

Chemical reactions produce an electrical potential energy difference between the 2 terminals resulting in a +ve charged terminal and a -ve charged terminal

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10
Q

If the poles of the cell are joined by a [ ], charges will flow

A

conducting path

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11
Q

Describe which charges flow in which directions

A

+ve charges flow from the +ve pole to the -ve pole, and -ve charges move the other way

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12
Q

Which charges are more likely in circuits?

A

As metals contain free electrons, which are -ve charged, the movement of -ve charges is more usual in a circuit

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13
Q

When charges move between 2 points in a circuit, their [ ] changes by amount ΔE

A

electrical potential energy

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14
Q

What is the equation of voltage (Using E,Q and W)?

A

V = ΔE / Q = W/Q

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15
Q

The P.d between ends of a wire will [ ] the free elctrons

A

Accelerate

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16
Q

What obstructs the free electrons moving down a wire?

A

By their interactions with the +ve ion cores of the metal atoms, so they don’t gain kinetic energy

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17
Q

What does the p.d lost by electrons obstructing do? What’s this called?

A

The p.d lost does work on the wire, heating it

This ‘wasted’ energy is called dissipation and the process is called ‘Joule Heating’

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18
Q

Combine the equations V=W/Q and I=Q/t

A
V = W/Q -> W = VQ
I = Q/t -> Q=It
W = V(It) - > W = VIt
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19
Q

What is the equation and units of power? (Using work done)

A

P = W/t = VIt/t = IV

Power (Js⁻¹ or W)

20
Q

What is power?

A

It is the rate at which energy is transferred

21
Q

What is the equation for resistance (voltage and current)?

A
R = V/I
V = IR
22
Q

What is the equation for power (w/ resistance)?

A

P = IV = (IR)I = I²R

23
Q

When there is a constant current in a conductor, the forward push of the moving charges from the p.d, between the ends of the conductor is balanced by the …

A

…obstructing effect of the atoms in the conductor interacting with the charges.

24
Q

What is the unit of resistance?

A

VA⁻¹ = Ω

25
What is resistance?
Is a measure of how difficult it is to get the current through the component
26
For most metals at a constant temp. the resistance is [ ]
Constant
27
What is Ohm's law?
I is proportional to V
28
A conductor that obeys Ohm's law is...
Ohmic
29
What is the equation for conductance (With Voltage)?Units?
G = I/V | AV⁻¹ or S (Siemen)
30
What is the equation of conductance (w/ Resistance)?
G = 1/R
31
Equation for conductance is a parallel circuit (including steps)
``` G = I/V G = I₁+I₂ / V G = I₁/V + I₂/V G = G₁ + G₂ ```
32
What is the equation for resistance in parallel?
1/R = 1/R₁ + 1/R₂ + ...
33
Equation for voltage in series?
V = V₁ + V₂ + ...
34
Equation for resistance in series?
R = R₁ + R₂ + ...
35
Equation for conductance in series?
1/G = 1/G₁ + 1/G₂ + ...
36
From a p.d - current graph, how can you tell if the component is ohmic?
If the line is straight (proportional) then the component is ohmic, otherwise non-ohmic
37
What are extensive properties?
Properties that depend on the dimensions or material of the thing (eg, wire)
38
What are intensive or bulk properties?
Properties dependant of dimensions.
39
Are resistance and conductance extensive or bulk properties?
Extensive
40
Give examples of bulk properties
Density, Young's modulus, Refractive index
41
What is σ?
σ = Electrical conductivity (Sm⁻¹)
42
What is ρ?
ρ = electrical resistivity (Ωm)
43
Conductance = (with sigma)
G = σA / L
44
Resistance = (w/ rho)
R = ρL / A
45
What are the 3 types of material?
Conductor, semiconductor and insulator
46
How can you measure the resistivity/conductivity of an insulator?
You need a tiny value of L, a large value of A, a large p.d, and a very, very sensitive ammeter.
47
How can you measure the resistivity/conductivity of an metal?
You need a large L and a very small A, and you must be aware of the complications cause by I²R heating of the wire and systematic errors such as p.d drops in places other than across the conductor in question