Current and Resistance

Question 1

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

Answer 1

Amount of charge passing through per unit time.

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

Question 2

What is the difference between Direct Current and Alternating Current

Answer 2

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

Question 3

What is Electromotive force(emf)?

Answer 3

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

Question 4

What is Junction Rule?

Answer 4

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)

Question 5

What is Loop Rule?

Answer 5

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

Question 6

What is a resistor and its formula?

Answer 6

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

Question 7

What is the relationship between Temperature and Resistance?

Answer 7

Proportional

Question 8

What is Ohm’s Law?

Answer 8

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

Question 9

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

Answer 9

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)

Question 10

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

Answer 10

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

Question 11

What is Power? Define in terms of Work and Energy

Answer 11

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

Question 12

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

Answer 12

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

Question 13

What is the difference between series and parallel circuit?

Answer 13

Series: connected linearly
Parallel: connected separately, divided

Question 14

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

Answer 14

Vs = V1 + V2 + V3…

Question 15

What is the Equation for the Resistance in Series circuit?

Answer 15

Rs = R1 + R2 + R3…

Question 16

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

Answer 16

Vp = V1 = V2 = V3…

Question 17

What is the equation for the Resistance in Parallel circuit?

Answer 17

Rp = 1/R1 + 1/R2 + 1/R3…

Question 18

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

Answer 18

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

Question 19

How to approach Parallel circuit questions?

Answer 19

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

Question 20

What is a Capacitor?

Answer 20

A device that can store charges on the plate

Question 21

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

Answer 21

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

Shows how much charge is present on the plate per voltage

Question 22

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

Answer 22

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

Question 23

What is the equation for Electric field created by capacitor?

Answer 23

E = V/d

Question 24

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

Answer 24

U = 1/2(CV^2)

Question 25

What are dielectric materials and how do they affect capacitance?

Answer 25

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.

Question 26

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

Answer 26

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

Question 27

What is the equation for Capacitance in series?

Answer 27

1/Cs = 1/C1 + 1/C2 + 1/C3... (acts like a big capacitor with large distance "d")

Question 28

What is the equation for Capacitance in Parallel?

Answer 28

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

Question 29

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

Answer 29

``` C' = kC k = dielectric constant ```

Question 30

What is the dielectric constant for vacuum?

Answer 30

k = 1. | dielectric materials always increase Capacitance