Question

What is the mathematical equation for capacitance? Identify each variable.

Answer 1

What is the mathematical equation for Ohm’s law? Identify each variable.

Answer 2

This would

Answer 3

This would be it right?

Answer 4

@Vocaloid

Answer 5

yes

Answer 6

well let's start with the force equation, what would multiplying the charge by 2 do and what would multiplying the distance by 2 do?

Answer 7

well distance is inverse

Answer 8

anf force is just parallel i think :/

Answer 9

good, so numerically, how would the force change if one charge is doubled?

Answer 10

4 and then one would reduce by 2?

Answer 11

hm

if one charge is doubled the equation just becomes F = 2q * q / r^2 so the force is just doubled from before

if the distance doubles then the equation becomes F = q * q / (2r)^2 so qq/4r^2 so it gets scaled down to 1/4 of the original force

Answer 12

what about the electric potential U? doubling a charge vs doubling the distance?

Answer 13

um not sure about this one

Answer 14

well, take the equation for U and multiply one of the charges by 2

what happens to the overall equation?

Answer 15

This equation right

Answer 16

yes

Answer 17

It would decrease

Answer 18

:/

Answer 19

Still not sure about this one

Answer 20

let's take q1 and multiply it by 2

Answer 21

what happens to the overall equation for U?

Answer 22

well its multilpied by two

Answer 23

good, so we would say the potential energy equation gets multiplied by 2 if the charge is doubled

now repeat the same thing except multiply the distance r by 2

Answer 24

SO the charge increase

Answer 25

well distance is inverse so the opposite?

Answer 26

good, doubling distance would reduce the original U by 1/2

Answer 27

what about the potential difference V?

Answer 28

it pretty much follows the same rule as U, if you double the charge you double the V, if you double r you cut the original V in half

Answer 29

good but instead of just saying "1/4" in the lower left corner it needs to be something like "reduces the force by a factor of 1/4"

Answer 30

Okay got it and for the top part where I wrote doubled it would be doubled by 2?

Answer 31

"doubled" already means increased by 2 so "doubled by 2" is redundant

Answer 32

What is the potential difference across a 15 Ω resistor that has a current of 3.0 A?

Answer 33

potential difference = V = IR

you're given current and resistance, find V

Answer 34

V=IR
V=3.0*15=45

Answer 35

awesome

units on potential difference are volts (V)

Answer 36

symbol is U

Answer 37

U is potential energy not potential difference (yeah the names are a bit confusing)

so potential difference has the symbol V and the name volts (i can't find an abbreviation for volts, so just "v"??)

Answer 38

*i guess it should be a capital V for the abbreviation too

Answer 39

Yeah thats what I pur ^~^

Answer 40

Okay for current I resistance it would be R

Answer 41

yes, and the full names for those would be amperes (amps) for current and ohms (idk how to abbreviate ohms)

Answer 42

oh wait duh the abbreviation would be the omega symbol (Ω)

Answer 43

anyway what about charge?

Answer 44

capacitance would be Um :/

Answer 45

capacitance has the symbol C, units of farads, abbreviation (F)

Answer 46

charge would be neg or pos

Answer 47

that's a good guess but those are types of charge, not necessarily the symbol we use to represent charge

if you look at the equations for force/potential energy/, etc. from before notice how we used "q" for charge, that would be your symbol

the units of charge are Coloumbs, usually abbreviated as C (to distinguisth between coloumbs and capacitance you have to pay attention to the context of the problem)

Answer 48

Going to bed? [=)

Answer 49

nah I'll be up for a while, I'm caught up on sleep

Answer 50

insulator for the first blank

Answer 51

copper is a conductor not an insulator (it allows for the flow of electrons)

Answer 52

insulator would be rubber

Answer 53

because it allows?

Answer 54

the third blank is talking about an insulator so it would *"prevent"* the flow of charges

Answer 55

material that partially conducts electricity is a semiconductor and I'm 80% sure the elements would be "metalloids"

Answer 56

good

Answer 57

well let's take the rows two at a time

between voltmeter and ammeter which one measures current and which one measures voltage?

Answer 58

voltmeter = voltage
ammeter = current

Answer 59

good

which one is in series and which one is in parallel?

Answer 60

current is parallel and the other is series

Answer 61

other way around, since resistors in parallel have the same voltage so the voltmeter needs to be in parallel and the ammeter in series

Answer 62

so moving on, which one's in amperes and which one's in volts?

Answer 63

amperes is obviously PD and the other is current

Answer 64

amperes is current, voltage is potential difference

Answer 65

good, all the x's are in the right spots

Answer 66

Write a few sentences comparing three different kinds of circuits: complete, open, and short circuits.

Answer 67

Open: allows matter to enter and exit

Answer 68

that's an open system not an open circuit

Answer 69

open circuit is light right?

Answer 70

open circuit = a circuit in which the flow of electrons has been interrupted by a break in the pathway

closed circuit = a circuit in which the flow of electrons has not been interrupted

Answer 71

Okay so the question is asking for complete, short, and open

Answer 72

complete would be where it is a completed circuit

Answer 73

yes

Answer 74

a short circuit is a circuit with too low resistance which causes the circuit elements to overheat, causing damage; this happens because electrons will naturally seek the path of lowest resistance

Answer 75

got it and my definiton for completed is correct right?

Answer 76

yes

Answer 77

Describe how fuses and circuit breakers protect against electrocution and household fires. How do you restore a broken circuit after the problem has been corrected?

Answer 78

Not sure about this

Answer 79

fuses are thin pieces of wire that will melt when overheated, interrupting excess current and opening the circuit
circuit breakers are switches that turn off and interrupt the flow of current when too much current is detected

I'm not 100% sure on how to restore a circuit, but apparently you just have to turn the circuit breaker to the off position and then on again, or, if you're using a fuse, replace the broken fuse with a new one

Answer 80

well let's start with A, do any of the bulbs still work if A is broken? (are there any loops that still work without bulb A?)

Answer 81

It would still work I think

Answer 82

so none of the bulbs work if A is out

what about bulb B?

Answer 83

b would work

Answer 84

good, if bulb B goes out, then A C and D are still in a loop

what about bulb C?

Answer 85

will not work

Answer 86

hm, if we burn out bulb C we still have a loop with A, B D

Answer 87

bulb D?

Answer 88

Its in the loop

Answer 89

good so if bulb D goes out they all go out

Answer 90

alright for part b, if you have three 10 ohm resistors in series what's the total resistance?

Answer 91

30 right because I would do 10*3

Answer 92

awesome

what about part c) if three 10 ohms are in parallel?

Answer 93

um 10+10+10 ? :/

Answer 94

remember the rule for parallel resistance

1/T = sum of 1/resistance for all resistors

Answer 95

1/T = 1/10 + 1/10 + 1/10

T = ?

Answer 96

oh okay so 1/10+1/10+1/10

Answer 97

3/10

Answer 98

be careful

1/T = 3/10 yes, but we still need to solve for T

Answer 99

10/3

Answer 100

for this would it just be 60/10

Answer 101

good, T = 10/3 which rounds to about 3.33 ohms for c)

Answer 102

alright for d) use the formula V = IR to find the current for the 30 ohm series resistors , and then for the 3.33 ohm parallel resistors (you are given V = 60 volts)

Answer 103

V=IR
60=I(30)
I=2

V=IR
60=I(3.33)
I=18

Answer 104

good

units of current are amps as usual

Answer 105

Going to bed now?? =)

Answer 106

nah I'll be up for an hour or so, I'm working on some notes for class

Answer 107

a. What are the ends of a magnet called? Describe the forces that occur when two magnets are brought close together. (1 point)

b. Draw a bar magnet, label its poles, and draw the magnetic field lines around it. (1 point)


c. Explain what happens when you cut a magnet in half. (1 point)

Answer 108

A. the ends of the magnet are called the north and south pole. When these are brought together, they repel against each other.
B.

Answer 109

I am not sure about part C

Answer 110

just be careful with part A, you must specify that they will repel each other if *like* ends (so north-north or south-south) are brought together, and will attract if opposite ends are brought together

Answer 111

for C, if a magnet is cut in half, each segment will form its own north and south pole

Answer 112

Compare permanent magnetism, induced magnetism, and electromagnetism.

Answer 113

Not sure about this. electromagnetism well has to do with electricity and magnets.>

Answer 114

permanent magnetism = type of magnetism in which magnet that still retains its properties even w/o an applied field

induced magnetism = type of magnetism in which a substance is induced to have a magnetic field after being exposed to an applied field, but the alignment of their atoms is not permanent and thus is not a permanent magnet

Answer 115

electromagnetism: magnetism that is induced by an applied electric current

Answer 116

generator: mechanical --> electrical
motor: electrical --> mechanical

Answer 117

third blank is transformer,
if primary coil # is > than secondary coil # it's a step-down transformer, if primary < secondary it's a step-up

Answer 118

can we close this and re-post this question in either the finance or the math section?

Answer 119

Not the phhysics section?

Answer 120

yeah this is an economics question so physics wouldn't be the right place, plus this question is already very long (130+ replies)

Answer 121

OH shoot , i posted the wrong thing. I have a physics question. I will repost it in physics