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PHYSICS > Current and Resistance > Flashcards

Current and Resistance Flashcards

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1
Q

What is Current? What is the formula that shows Current?

A

Amount of charge passing through per unit time.

I = Q/dt (A; C/s)

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2
Q

What is the difference between Direct Current and Alternating Current

A

Direct current is flow in one direction ex. battery and Alternating Current is change direction of flow ex. household

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3
Q

What is Electromotive force(emf)?

A

Potential difference(V) that tends to give rise to current

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4
Q

What is Junction Rule?

A

At a junction, the sum of current INTO the path is equal to the sum of current that comes OUT
I(into junction) = I(out junction)

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5
Q

What is Loop Rule?

A

The sum of all voltages in a closed circuit must be “0”
V(source) = V(drop)
V(lift) = gives positive V
V(resistors) = gives negative V

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6
Q

What is a resistor and its formula?

A 
Resistor is a conductor that allows Voltage drop.
R = ρL/A (unit: Ohms)
ρ: Resistivity
L: Length
A: Cross Sectional Area
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7
Q

What is the relationship between Temperature and Resistance?

A

Proportional

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8
Q

What is Ohm’s Law?

A

V = IR (unit: V)
I: Current
R: Resistance

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9
Q

What is internal resistance and What is the actual voltage provided in the cell?

A

r(int) is present in every E(cell)/battery.
V = E(cell) - ir(int)
E(cell) is emf of cell, provides Voltage(+)
ir(int) is the Voltage drop(-)
V = E(cell) - ir(int)

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10
Q

In which direction does the current flow in convention and in reality?

A

Convention: movement of proton…low to high V(- to +)
Reality: movement of electrons…high to low V(+ to -)

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11
Q

What is Power? Define in terms of Work and Energy

A

Power is how fast energy is being transferred(energy = work)
P = W/t
P = dE/t

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12
Q

What is Power in terms of Current and Voltage and Resistance?

A 
P = IV 
P = I^2R
P = V^2/R
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13
Q

What is the difference between series and parallel circuit?

A

Series: connected linearly
Parallel: connected separately, divided

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14
Q

What is the equation for the Voltage drop in Series circuit?

A

Vs = V1 + V2 + V3…

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15
Q

What is the Equation for the Resistance in Series circuit?

A

Rs = R1 + R2 + R3…

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16
Q

What is the equation for the Voltage drop in Parallel circuit?

A

Vp = V1 = V2 = V3…

17
Q

What is the equation for the Resistance in Parallel circuit?

A

Rp = 1/R1 + 1/R2 + 1/R3…

18
Q

What is the difference in terms of Current between Series and Parallel circuits?

A

Series: Current is the same in each resistor
Parallel: Current might differ depending on R values(As R goes up, I decreases)

19
Q

How to approach Parallel circuit questions?

A

1) Get Total Voltage
2) Total Resistance
3) Total Current

20
Q

What is a Capacitor?

A

A device that can store charges on the plate

21
Q

What is the equation for Capacitance in terms of charges? What does it show?

A

C = Q/V (unit: 1F = 1C/V)

Shows how much charge is present on the plate per voltage

22
Q

What is the equation for Capacitance in terms of physical geometry of the plates?

A

C = ε(A/d)
ε: 8.85 x 10^-12 F/m
d: distance between the two plates
A: Cross sectional area of the plates’ overlap

23
Q

What is the equation for Electric field created by capacitor?

A

E = V/d

24
Q

What is the equation for Potential energy stored in a capacitor?

A

U = 1/2(CV^2)

25
Q

What are dielectric materials and how do they affect capacitance?

A

They are insulators and placed between the plates to help increase Capacitance by Capacitors. They prevent charges from flowing and isolate Negative charges(Q-) and Positive charges(Q+) from each other.

26
Q

What are the two cases of how dielectrics can affect Capacitance by Capacitors?

A

1) Isolated Capacitor(w/out battery, or taken out later)
…C = Q/V, Increase C by lowering V but Q remains same
2) Circuit Dapacitor(w/ battery)
…C = Q/V, Increase C by increasing Q but V remains same

27
Q

What is the equation for Capacitance in series?

A

1/Cs = 1/C1 + 1/C2 + 1/C3… (acts like a big capacitor with large distance “d”)

28
Q

What is the equation for Capacitance in Parallel?

A

Cp = C1 + C2 + C3…(acts like a separate capacitor)

29
Q

What is the equation for the “new” capacitance after a dielectric material has been inserted between capacitor plates?

A 
C' = kC
k = dielectric constant
30
Q

What is the dielectric constant for vacuum?

A

k = 1.

dielectric materials always increase Capacitance

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