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Physics SUM 1 > MC Test 2 > Flashcards

MC Test 2 Flashcards

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1
Q

What is Electricity?

A
  • The collection or flow of electrons in the form of an electric charge
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2
Q

Static Electricity

A
  • When two objects rub against each other, electrons transfer and build up on an object causing it to have a different charge from its surroundings
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3
Q

Electricity example

A
  • Often when you remove clothes from the dryer, they seem to stick together. This is because some of the clothes have gained electrons by rubbing against other clothes. The clothes losing electrons become positive. The negative clothes are attracted to the positive clothes
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4
Q

Conductor

A
  • A material which allows an electric current to pass. Metals are good conductors of electricity
  • the materials in which some of the negative charge can move rather freely
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5
Q

Insulator

A
  • A material which does not allow electric current to pass. Non-metals are not good condutors of electricity. Plastic, glass, wood and rubber are good insulators.
  • The materials in which none of the charge move freely
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6
Q

Semiconductors(Nonconductors)

A
  • The materials that are intermediate between conductors and insulators
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7
Q

Describe the simple or electric battery?

A

An example of simple battery would be one in which zinc and carbon are used as electordes while a dilute acid such as sulfuric acid (dilute) acts as the electrolyte. The acid dissolves the zinc and causes zinc ions to leave the elctrode. Each zinc ion which enters the electrolyte leaves 2 electrons on the zinc plate. The carbon electrode also dissolves but at a slower rate. The result is a differnce in potential between the 2 electrodes. Carbon electrode is positve and Zinc electrode is negative

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8
Q

Kirchhoffs’ Current Law

A
  • At any point in an electrical cirucuit that does not represent a capacitor plate, the sum of currents flowing towards that point is equal to the sum of currents flowing away from that point
  • i1+i4=i2+i3
  • sum of ik= 0 if k=1
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9
Q

Kirchhoff’s Voltage Law

A
  • The directed sum of electrical potential differences around any closed circuit must be zero
  • sum of Vk=0 if k=1
  • v1+v2+v3+v4=0
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10
Q

Circuits can be rearranged, wires with negligible resistance can be….

A
  • stretched, bended or collapsed to a point
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11
Q

What are electrical circuits?

A
  • typically contain a voltage source, wire conductor and one or more devices which use the electrical energy
  • there is the series circuit and parallel circuit
  • need free charge = electric circuit must consist of conductive material(wires)
  • Must be closed
  • Battery supplies constant potential difference(voltage)
  • Battery converts chemical energy to potential energy
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12
Q

Series Circuit

A
  • One which provides a single pathway for the current to flow. If the circuit breaks, all devices using the circuit wall will fail
  • Charge conservation: I=I1=I2=I3
  • Ohm’s law: V1=IR1; V2=IR2; V3=IR3
  • Energy Conservation: qV=qV1+qV2+qV3, V=V1+V2+V3
  • IReq=IR1+IR2=IR3
  • Req=R1+R2+R3
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13
Q

Electric Power

A
  • equals product of the current I and the potential difference V
  • P=IV
  • The SI unit is Watt(W) where 1 (kilowatt) kw = 1000W
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14
Q

Current modulations

A
  • PC and AC can be modulated and these modulations can be in amplitude and in frequency
  • Amplitude Modulation: variation in the peak intensity in a series of pulses or cycle
  • Frequency Modulation: a variaion in the instantaneous frequency of the wave
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15
Q

Rise time

A
  • the time for the leading edge of the phase to increase from the baseline to the peak amplitude of the phase
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16
Q

Pulse duration

A
  • the time elapsed from the beginning to the end of all phases in one pulse
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17
Q

Interpulse Interval

A
  • the time between 2 successive pulses
18
Q

Phase

A

the current flow in 1 direction for a finite period of time

19
Q

Phase duration

A

the time elapsed from the beginning to the end of 1 phase

20
Q

Interphase Interval

A
  • the time between 2 successive components of a pulse when no electrical activity occurs
21
Q

Waveform

A
  • the visual representation of current or voltage. The waveform of a current simply reers to its shape as seen on a graph of amplitude versus time
  • Monophasic and Biphasic(symmetrical or assymetrical)
22
Q

Monophasic Waveform

A

the current flows in 1 direction therefore one electrode acts as the cathode(negative) while the other acs as anode(positive)

23
Q

Biphasic Waveform

A
  • The current flows in both directions so each electrode acts as a cathode for some part of the waveform
  • Symmetrical: the portion of the waveform in the first phase is an exact mirror image but opposite in direction to the portion of the waveform in the second phase
  • Assymetrical: the phases are not equal in shape
24
Q

Frequency

A
  • A number of pulses delivered per second, It is measured in Hertz(Hz) or in pulses per second(pps)
  • f=1/T(period) where T= tp+ti
  • Example: a frequency of 150 Hz means that 150 pulses are delivered per second
25
Q

Period

A
  • The time elapsed between a special point on the waveform of the pulse to the identical point on the next pulse.
  • In pulsed current the period equals the pulse duration plus the interpulse interval
  • In alternating current the waveform duration is = to 1 period(one complete cycle)
26
Q

Ohm’s Law

A
  • Current flowing through a conductor is directly proportional to the potential difference at its ends and inversely proportional to the resistance of the conductor
  • I (Amps) =V (Volts) / R (Ohms)
  • predicts the current in an ideal ressitor or other ohmic device to be applied voltage divided by resistance
27
Q

Voltage(aka. electric or electrical tension)

A
  • The driving force required to move electric charges. It is measured in volts(V).
  • V=IR
  • The difference of electrical potential between 2 points of an electrical or electronic circuit expressed in volts
  • Depending on the difference of electrical potential it is called extra low voltage, low voltage, high voltage or extra high voltage
28
Q

Electrical Resistance(Impedance) and measuring Resistivity

A
  • The ability if a substance to prevent or resist the flow of electric current
  • R=V/I
  • Electrical resistance is a measure of the degree to which an object opposes an electric current through it
  • measured n ohms
  • is parameter which opposes the movement of electric charges
  • Resistivity: R=pL/A where p is measured in ohms, L is the length o the conductor (vd Δt) and A is the area
29
Q

Intensity

A
  • The ratio of electric charge flowing through any cross section of the wire
  • I=q/t
30
Q

Alternating current(AC)

A
  • the flow of electric charge that periodically reverses direction
  • direction and intensity are not constant
  • if ratio of intensity(I=q/t) varies over time it is AC
  • in which bidirectional current flows continuously over time
31
Q

Pulsed current(PC)

A
  • one in which undirectional or bidirectional flow of current periodically ceases over time
  • intensity isnt constant but direction can be constant
32
Q

Direct current(DC)

A
  • The flow of electric charge that does not change direction or values of intensity at the time of flow
  • Direction and intensity are constant
  • The ratio of intensity(I=q/t) is constant so DC
  • in which undirectional current flows continously over time
33
Q

Amplitude

A
  • the measure of max value of current with reference to the baseline
  • is termed intensity
34
Q

Intensity

A
  • the magnitude of current or voltage applied by the unit and can be measured in milliamps(mA)
35
Q

Ohmic Heating

A

flowing electrons strike atomsin a conductor, heating the material

36
Q

Parallel circuit

A
  • has multiple pathways for the current to flow
  • If the circuit is broken the current may pass through other pathways and other devices will continue to work
  • Charge conservation: I=I1+I2+I3
  • Energy conservation: V=V1=V2=V3
  • Ohm’s law: I1=V/R1; I2=V/R2; I3=V/R3
  • V/Req=V/R1+V/R2+V/R3
  • 1/Req = 1/R1+1/R2+1/R3
37
Q

Closed Circuit

A
  • one in which the pathway of electrical current is complete and unbroken
38
Q

Open Circuit

A
  • one in which the pathway of the electrical current is broken.
  • A switch is a device in the circuit in which the circuit can be closed(turned on) r open(turned off)
39
Q

Current density(J)

A
  • A measure of the density of electrical current
  • J= I/S (A/m2)
  • defined as a vector whose magnitude is the electric current per cross sectional area
  • measured in amperes/ square meter
40
Q

Resistors

A
  • a 2 terminal electronic component designed to oppose an electric current by producing a voltage drop between its terminals in proportion to the current
41
Q

Resistance and Temperature

A
  • When electrons move through the conductor they collide with atom:
    • Temperature of the conductor increases because of the current(through collision)
    • Electrical energy is transformed into thermal energy
    • Resistors dissipate energy
    • Power- energy per unit of time (W=J/s) dissipated by a resistor
    • P = I2 R

Physics SUM 1 (2 decks)

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