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ELEC1111 > Topic 1 > Flashcards

Topic 1 Flashcards

Chapters 1 & 2 of Textbook (84 cards)

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1
Q

Frequency

A

Unit name: Hertz
Expression: seconds^-1
Symbol: Hz

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2
Q

Electric Current

A

Unit Name: Amps
Expression: Coulombs/second
Symbol: A

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3
Q

Force

A

Unit name: Newtons
Expression: kilograms x metres/seconds^2
Symbol: N

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4
Q

Energy (work)

A

Unit name: Joules
Expression: Newtons x metres

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5
Q

What is work?

A

Measure of energy transfer by a force

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6
Q

Electric Potential

A

Unit name: Volts
Expression: Watts/Amps or joules/coulombs or Newtonsxmetres /coulombs
Symbol: V

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7
Q

Lumimous Intensity

A

Unit Name: Candela
Symbol: Cd

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8
Q

Resistance

A

Unit Name: Ohms
Expression: Volts/Amps
Symbol: Ω

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9
Q

Electric Charge

A

Unit name: Coulombs
Expression: Amps x seconds
Symbol: C

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10
Q

Power

A

Unit Name: Watts
Expression: Joules/seconds and Volts x Amps
Symbol: W

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11
Q

Conductance

A

Unit Name: Siemens
Expression: Amps/Volts (reciprocal of resistance)
Symbol: S

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12
Q

Capacitance

A

Unit Name: Farad
Expression: Coulombs/Volts
Symbol: F

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13
Q

Magnetic Flux

A

Unit Name: Weber
Expression: Volts x seconds
Symbol: Wb

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14
Q

Inductance

A

Unit Name: Henry
Expression: Webers/Amps
Symbol: H

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15
Q

What is frequency?

A

It represents time variation of a waveform. It measures the number of waves that pass a fixed point in a second.

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16
Q

What is power?

A

The rate at which work is done/energy is transferred. Measured in watts.

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17
Q

What do coulombs measure?

A

They are the unit for electric charge, equal to the amount of charge from a current of one amp flowing for one second.

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18
Q

What is resistance?

A

How a component opposes the flow of a current.

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19
Q

What does one coulomb measure?

A

Total charge possessed by 6.25 x 10^18

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20
Q

What charge to protons carry?

A

Positive charge of electrons, being 1.6x10^-19

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21
Q

Notation for charge?

A

Q: Constant charge
q(t) or q: Instantaneous or time-varying charge

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22
Q

What is the law of conservation of charge?

A

Charge cannot be created or destroyed, only transferred.

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23
Q

What is current?

A

Essentially the flow of electrons in circuit. But it is not exactly the flow, it is the flow of charge. It is measured in coulombs per second (Amps), so charge flowing through an area per second.

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24
Q

What is required of a material for a current to be run through it?

A

The material requires free charges, in free moving electrons. Glass and plastic have tightly bound electrons, and are insulators. Metals have free flowing electrons, and are conductors.

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25
How is an electric current started?
It is created by a voltage (a difference in electric potential). Electrons travel from areas of low potential to high potential creating an electric current.
26
What is element is this?
Resistor
27
What is element is this?
Capacitor
28
What is a circuit?
A path that allows electric currents to flow through.
29
What provides voltage?
Power sources like batteries provide voltage that drive the current. The power source will have one end with high potential, and one with low.
30
What is element is this?
Inductor
31
What is element is this?
Switch
32
What element is this?
Variable resistor
33
What is this?
LED
34
What is this?
Battery
35
Explain why electrons travel from low potential to high potential.
For negative charges, since the electrons are repelled from the negative end and attracted to the positive end, the area where the electrons have the highest potential energy will be at the negative end of the battery. However, we use the positive direction as the reference for moving down in potential. This results in negative charges appearing that they are moving up the electric potential, but they are not.
36
What direction does the conventional current travelling?
Whichever way the net flow of positive charges are going. This means that the "conventional current" flows opposite to electron flow.
37
Notation for currents?
I : constant current i(t) or i: Instantaneous or time-varying current
38
How do you calculate a charge given a current?
Since the current is the rate of change of electric charge over time, i is defined as dq/dt. Thus, charge can be calculated from current by integrating.
39
DC vs AC current
A direct current flows only in one direction, but may be constant or time-varying. An alternation current changes directions with respect to time. Looks like a wave.
40
What do negative amps mean when measuring a current?
Happens only in AC circuit, where the current is now flowing in the opposite direction to what was initially defined as positive.
41
What is voltage equation?
Defined as the energy (w) required to move a unit of charge (q) from a reference point to another point. Therefore, v = dw/dq.
42
DC vs AC voltages
DC voltage (V) : A voltage with a fixed polarity. Normally produced by batteries. AC voltage (v) : Time-varying voltage with alternating polarity over time. Normally produced by generators.
43
Ohm's Law
44
Common SI prefixes
mega (M) - 10^6 kilo (k) - 10^3 milli (m) - 10^-3 micro (µ) - 10^-6
45
What is the relationship between current, charge and time?
Current is measured in Amps.
46
How do you calculate charge from current and time?
Integrate the equation, to get
47
What is an ammeter?
Ammeters measure electric current. Which is in amps.
48
What is a voltmeter?
Measures voltage.
49
What is an electromagnet?
50
How much charge is in one electron?
-1.602 x 10^-19 C
51
What is the voltage between two points a and b mathematically expressed as?
Where w is energy in joules and q is charge in coulombs.
52
What is a capacitor?
A capacitor can store and release electrical energy much faster than a battery, but cannot store as much. Acts like a water tank.
53
What is a resistor?
Limits or regulates the flow of electrical current in an electronic circuit.
54
What is a transistor?
55
What is the expression of power? Power is the rate at which...
Where p is power in watts (W), w is energy in joules (J) and t is time in seconds (s).
56
W vs w
W is the measurement unit for power, watts. w is the pronumeral representing energy, which is measured in joules (J).
57
How do we relate power and energy to voltage?
Where p is power in watts (W), v is voltage in volts (V) and i is current, measured in amps.
58
When is power (p) positive/negative?
Positive when an element is being supplied with power. Negative when the element is supplying power.
59
l
60
What does the law of conservation of energy state in regards to an electric circuit?
The algebraic sum of power in a circuit at any time must be zero.
61
How do you calculate energy from power? What are the units in?
Where w is energy in joules (J), power is in watts (W), v is voltage (v) and i is current (A), t is in seconds.
62
What is a watt-hour?
63
What does it mean when power is positive/negative?
Positive = Power absorbed or dissipated Negative = Supplied or generated Look at which terminal the current is entering. Entering positive is absorbed, entering negative is supplied.
64
Which way should a current enter a battery?
Into the negative terminal
65
What is the difference between these two voltage sources?
a) can represent both constant and time-varying voltage source, while b) can only be used to represent a constant voltage source.
66
What is this?
Symbol for an independent current source.
67
What is this?
A dependent voltage source and current source.
68
Reference polarities?
69
Ideal vs Real sources?
Ideal - Can generate/dissipate infinite power. Voltage sources have no resistance. Current sources have an infinite internal resistance. Real - Real voltage sources have an upper current limit, and current sources have an upper voltage limit. Voltage sources have a low, but non-zero resistance. Current sources have a very high, but non-infinite internal resistance.
70
Series vs Parallel circuit for voltage and current
Series circuit: The current is the same through each component, while the voltage is divided across them. Parallel circuit: the voltage is the same across each component, while the current is divided among them.
71
How do you calculate resistance of a conducting wire?
Where R is resistance, p is the materials resistivity, l is its length and A is cross-sectional area.
72
What is Ohm's law?
Where v is voltage, R is resistance and i is current.
73
What is conductance?
Reciprocal of resistance, ability to conduct electric current. Conductance (G) is measured in Siemens (S)
74
Fixed vs variable resistors?
Most resistors are fixed, meaning their resistance stays the same. Variable resistors can change their resistance value.
75
What are the two forms of the power equation for resistors?
76
What is a short circuit?
When a circuit element has almost zero resistance. Voltage is zero, but current can be anything. This is bad, as a very large amount of current will flow to somewhere unintended, resulting in a dangerous overload in the circuit.
77
What is an open circuit?
An element that has infinite resistance is an open circuit. Current is zero, but voltage could be anything, as resistance is infinite.
78
What is a diode?
A semiconductor that allows the flow of current in only one direction, flowing in the direction of the arrow. Anode is on positive terminal, cathode is at negative terminal.
78
What is this?
The required voltage for a diode to work. If the supplied voltage is higher than vd, the diode is forward biased, behaving as a voltage source. If the supplied voltage is less than vd, the diode is reverse biased, and create an open circuit.
79
Types of diodes?
LEDS (light emitting diodes) Small signal diodes Power Diodes Laser diodes Photodiodes
80
Ideal independent vs dependent source
Ideal Indep: An active element that provides a specified voltage or current independent of other circuit elements. Ideal dependent: An active element in which source quantity is controlled by the voltage or current. E.g. Transistors, operational amplifiers
81
Passive vs Active element
Active: Capable of generating energy E.g. Batteries, generators, operational amplifiers Passive: Can't generate energy E.g. Resistors, capacitors, inductors
82
Power equations in terms of resistance?
83
Power, energy, charge, time, voltage and current relationship.

ELEC1111 (7 decks)

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