Ch 6 - Circuits Flashcards

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1
Q

What is a current?

A

the movement of charge that occurs between 2 points that have different electrical potentials ( A = C/s)
I = Q/t

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2
Q

What is the difference between the conventional definition of a current and reality?

A
  • by convention, current is defined as the movement of positive charge from the high potential end of a voltage source to the low potential end
  • in reality, it is negatively charged particles (electrons) that move in a circuit, from low potential to high potential
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3
Q

Where does currents flow?

A

only in conductive materials

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4
Q

What is the difference between metallic conduction, electrolytic conduction, and insulators?

A
  • metallic relies on uniform movement of free electrons in metallic bonds
  • electrolytic relies on the ion concentration of a solution
  • insulators are materials that do not conduct a current
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5
Q

What is Kirchhoff’s law?

A

express conservation of charge and energy

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6
Q

What is Kirchhoff’s junction rule?

A

states that the sum of currents directed into a point within a circuit equals the sum of the currents directed away from that point
I into junction = I leaving junction

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7
Q

What is Kirchhoff’s loop rule?

A

states that in a closed loop, the sum voltage sources is always equal to the sum of voltage drops
- if all the voltage wasn’t used up in each loop of the circuit, then the voltage would build after each trip around the circuit, which is impossible
V source = V drop
- the total potential difference around any closed loop is 0

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8
Q

What is resistance?

A

opposition to movement of electrons through a material
R = (resistivity x length)/cross sectional area
R = pL/A

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9
Q

What are resistors?

A

conductive materials with a moderate amount of resistance that slow down electrons without stopping them

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10
Q

What is Ohm’s law?

A

states that for a given resistance, the magnitude of the current through a resistor is proportional to the voltage drop across the resistor
V = IR

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11
Q

What is the purpose of combining resistors in a circuit and how can they be combined?

A
  • can be combined to calculate the equivalent resistance of a full or partial circuit
  • resistors in series are additive and sum together to create the total resistance of a circuit
  • resistors in parallel cause a decrease in equivalent resistance of a circuit
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12
Q

What does the amount of dissipated power across each resistor in a circuit depend on?

A

dependent on the current through the resistor and the voltage drop across the resistor

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13
Q

What are capacitors?

A

have the ability to store and discharge electrical potential energy

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14
Q

How is capacitance in parallel plate capacitors determined?

A

by the area of the plates and the distance between the plates

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15
Q

What do capacitors in series cause?

A

a decrease in the equivalent capacitance of a circuit

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16
Q

What do capacitors in parallel create?

A

they sum together to create a larger equivalent capacitance

17
Q

What are dielectric materials?

A

insulators placed between the plates of a capacitor that increase capacitance by a factor equal to the material’s dielectric constant, k
C’ = kC
- can never decrease capacitance, k never less than 1

18
Q

What are ammeters?

A

inserted in series in a circuit to measure current; they have negligible resistance
- minimum impact on circuit

19
Q

What are voltmeters?

A

inserted in parallel in a circuit to measure a voltage drop; they have very large resistance
- minimum impact on circuit

20
Q

What are ohmmeters?

A

inserted around a resistive element to measure resistance; they are self powered and have negligible resistance

21
Q

What is voltage?

A

potential difference between 2 points (Volts = J/C)

22
Q

What is electromotive force (emf)?

A

the potential difference of the voltage source for a circuit, usually a battery, and is given in volts

23
Q

What is conductivity?

A

the reciprocal of resistance and is a measure of permissiveness to current flow, measured in siemens (S)

24
Q

Which likely has a higher conductivity and why: 1 M glucose and 0.25 M NaCl?

A

NaCl higher because it is a salt and will increase the ion content of water
- glucose does not dissociate, and therefore it has a near zero impact on conductivity

25
Q

How is the power of a resistor or collection of resistors calculated?

A

P = IV = I^2R = V^2/R

26
Q

How are resistors calculated in series v in parallel?

A
  • in series: Rs = R1 + R2 + R3…

- in parallel: 1/Rs = 1/R1 + 1/R2 …

27
Q

How does adding or removing a resistor change the total resistance of a circuit with resistors in series? in parallel?

A
  • adding a resistor in series increases the total resistance of a circuit; removing one in a series decreases the total resistance in the circuit
  • these relationships are reversed in parallel: adding a resistor decreases resistance while removing one increases it
28
Q

How does internal resistance affect the voltage of the circuit?

A
  • it will lower the available voltage which will also lower current for any given resistance
29
Q

What is capacitance?

A

the ratio of the magnitude of the charge stored on one plate to the potential difference (voltage) across the capacitor
C = Q/V

30
Q

How are capacitors calculated in series v in parallel?

A
  • series: 1/Cs = 1/C1 + 1/C2 …

- parallel: Cp = C1 + C2 …

31
Q

Assuming the plates are attached by conducting material, how does a capacitor behave after the voltage source has been removed from a circuit?

A

the capacitor discharges, providing a current in the opposite direction of the initial current

32
Q

How does a dielectric material impact capacitance?

A

always increases capacitance

33
Q

How does a dielectric material impact voltage?

A
  • if capacitor is isolated, voltage will decrease

- if capacitor is in circuit, voltage is constant because it is dictated by the voltage source

34
Q

How does a dielectric material impact charge?

A
  • if capacitor is isolated, charge will remain constant because there is no additional source of charge
  • if capacitor in circuit, charge will increase
35
Q

How does adding or removing a capacitor change the total capacitance of a circuit with capacitors in series? in parallel?

A
  • adding a capacitor in series decreases the total capacitance of a circuit, removing one in a series increases total capacitance
  • reversed in parallel: adding capacitor increases capacitance, removing decreases it
36
Q

What physical qualities contribute to the capacitance of a capacitor?

A

surface area, distance, and dielectric constant

C = Q/V