Physics Lesson - Charge and Current (Q=It)
Summary
TLDRThis script discusses the frustration of waking up to a dead phone in a world where constant connectivity is the norm. It simplifies the phone charging process, explaining how electrons flow from a charger to the device. The video introduces Ohm's law to illustrate current flow and resistance, and uses it to differentiate between two wires. It further defines electric current as the charge flowing past a point per unit time, using the formula I = Q/T. A practical example is given to calculate current through a light bulb. The script concludes with advice on using external batteries to keep devices charged, emphasizing the importance of milliamp hours for capacity.
Takeaways
- 😖 The worst feeling is waking up to a dead phone, as it feels like losing a part of oneself due to the constant connectivity in the 21st century.
- 🔌 A phone charges through the flow of electrons from a charging device, gaining charge as they move into the phone.
- 🤔 To determine the electric current, one can visually assess two wires or use Ohm's law (I = V/R) to understand the relationship between voltage, resistance, and current.
- 💡 Ohm's law suggests that increasing voltage can double or triple the current flow, assuming resistance remains constant.
- 🔋 The amount of charge flowing past a point per unit time defines electric current, measured in amperes (amps).
- ⏱ The formula for current, I = Q/T, relates charge (in coulombs), time (in seconds), and current (in amps).
- 🔄 The rearranged formula, Q = I * T, is key to solving problems related to cell phone charging efficiency.
- 💡 A sample calculation demonstrates using the formula to find the electric current flowing through a light bulb given the charge and time.
- 🔌 External batteries or chargers can be used to keep devices charged, especially when away from a power source.
- 🔋 The capacity of an external charger is measured in milliamp hours (mAh), which is a unit of charge.
- 🛒 When choosing an external charger, look for one with a high mAh rating to ensure it can supply current for an extended period.
Q & A
What is the worst feeling described in the script related to technology?
-The worst feeling described is waking up and realizing you forgot to charge your phone, which can feel like losing a part of oneself due to the reliance on being interconnected with the world 24/7.
What is the basic principle of how a phone gets charged?
-A phone gets charged when electrons flow out of a charging device into the phone, causing the phone to gain charge.
What is Ohm's law and how is it relevant to understanding phone charging?
-Ohm's law is represented as I = V/R, where I is the current, V is the voltage, and R is the resistance. It's relevant to phone charging as it explains how the flow of electrons (current) is influenced by the voltage and resistance in the charging process.
How does the script suggest visualizing the difference in electric current between two wires?
-The script suggests that one can visually determine the difference in electric current by comparing the wires and guessing which one has more current flow, based on the appearance of the wires.
What is the mathematical relationship between voltage and current according to the script?
-The script explains that doubling the voltage would double the current, and tripling the voltage would triple the current, assuming resistance remains constant.
How is electric current defined in the script?
-Electric current is defined as the amount of coulombs of charge that flow past a certain point each second.
What is the formula for calculating electric current in terms of charge and time?
-The formula for calculating electric current is I = Q/T, where I is the current, Q is the charge in coulombs, and T is the time in seconds.
How can the formula Q = I * T be rearranged to solve for the charge (Q)?
-The formula can be rearranged to solve for the charge by dividing both sides by the current (I), resulting in Q = I * T.
What is the purpose of an external battery or charger as mentioned in the script?
-An external battery or charger is used to store charge and provide additional power to devices like smartphones, helping to keep them charged when a wall outlet or computer is not available.
What is a milliamp hour and how is it related to the charging capacity of an external battery?
-A milliamp hour is a unit of charge, representing the amount of current (in milliamps) that can be supplied for one hour. It is used to describe the capacity of an external battery to hold and supply charge.
What advice does the script give for keeping a phone charged more efficiently?
-The script recommends purchasing an external battery or charger with a high milliamp hour rating to ensure it can supply sufficient current for an extended period.
Outlines
🔋 The Frustration of a Dead Phone Battery
The paragraph discusses the common frustration of waking up to find a phone with a dead battery, emphasizing the feeling of disconnection from the world due to our reliance on constant connectivity. It introduces the topic of phone charging, explaining the basic concept of electrons flowing from a charging device into the phone. The paragraph uses Ohm's law (I = V/R) to illustrate the relationship between voltage, resistance, and current, suggesting that differences in voltage could be the reason for variations in current flow between two wires. It also introduces the concept of electric current as the flow of charge over time, using the formula I = Q/T to define current in terms of charge (Q) and time (T), and rearranges it to Q = I*T to relate to phone charging efficiency.
🔌 Understanding and Improving Phone Charging with External Batteries
This paragraph builds upon the previous discussion of electric current and applies it to the practical issue of keeping mobile devices charged. It provides a step-by-step calculation to determine the electric current flowing through a light bulb using the formula Q = I*T, converting minutes into seconds to find the current in amps. The paragraph then suggests the use of external batteries or chargers as a solution for those who struggle with keeping their devices charged throughout the day. It explains the concept of milliamp hours as a unit of charge, highlighting the importance of choosing an external charger with a high milliamp hour rating to ensure longer charging duration, and ends with advice on shopping wisely for such devices.
Mindmap
Keywords
💡Interconnectedness
💡First World Problem
💡Electrons
💡Ohm's Law
💡Voltage
💡Resistance
💡Current
💡Coulombs
💡External Battery
💡Milliamp Hours (mAh)
Highlights
The worst feeling is waking up to a dead phone, symbolizing a disconnection from the world.
Phones are charged through the flow of electrons into the device.
Ohm's Law (I = V/R) explains the relationship between voltage, resistance, and current.
Visual cues can suggest the difference in current flow between two wires.
Doubling the voltage can double the current, as per Ohm's Law.
Current is defined as the amount of charge (coulombs) flowing per second.
The formula I = Q/T relates current, charge, and time.
Q = I * T is a rearranged formula useful for calculating charge based on current and time.
External batteries or chargers can store charge to extend device usage.
Milliamp hours (mAh) is a unit of charge, indicating how much current can be supplied over time.
Higher mAh ratings in external chargers mean longer charge duration.
Shopping wisely for external chargers involves balancing cost and capacity.
Understanding electrical current can help in making informed decisions about charging devices.
The formula Q = I * T is key to solving problems related to phone charging efficiency.
Algebra skills are essential for rearranging and applying the charge formula effectively.
A formula triangle can be a helpful tool for beginners to learn algebraic manipulation.
The video concludes with practical advice on using external chargers to combat 'first world problems' like dead phone batteries.
Transcripts
you know what the worst feeling in the
world is waking up and realizing you
forgot to charge your phone it just
stinks because we're all so used to
feeling interconnected with the world
around us 24/7 that were not it feels
like we've lost a part of ourselves now
maybe a bit of a first world problem and
something that only those of us who have
grown up in the 21st century have had to
deal with but it is something that's
quite irritating and so there are ways
of getting around it other than just
being very diligent about how often you
charge your phone we'll talk about that
once we've gotten a little bit more
familiar with how current and charged
work so how does a phone actually get
charged well to way oversimplify it
electrons basically flow out of a
charging device into your phone and then
your phone gains charge so what does
that look like well if I ask you a
question like this where I show you two
different wires with two different
amounts of current and I say which wire
has the greatest electric current after
looking at both of them for a few
seconds a and B you should be able to
figure out that B has more current flow
than a now that's purely from a visual
standpoint you could guess that but
there's other ways of justifying it too
with equations one equation we've
already learned by this point that you
should be able to use to justify the
fact that there is more current B is
called Ohm's law Ohm's law is usually
displayed this way I equals V over R and
I equals V over R tells us that when
there is a voltage that is pushing
electrons through a wire there will be
some internal resistance that tries to
block the electrons and keep them from
flowing and when that voltage and
resistance fight each other in are in
conflict the end result is how much
current flow we get so that current flow
seems to be greater in B than in a so we
could assume well perhaps there's double
the voltage in B maybe there's two
batteries hooked up instead of one so
there's more of a push to get more
electrons through doubling the voltage
would double the current so that's kind
of like the old way of thinking about
how those two wires are different from
each other it doesn't really seem likely
that the resistance would be any
different because those wires look very
similar to each other but the voltage
could be different which would change
the current flow so this mathematical
example just says doubling the voltage
would double the current but tripling it
would triple the current as well so
there's our old relationship it's a new
way of thinking about electrical current
then one that will be useful for us when
were thinking about how to charge our
is to ask ourselves how much charge is
flowing past a certain point every unit
of time so here's what I mean by that we
can define what current is better than
we ever have thus far by saying the
current literally is the amount of
coulombs of charge that flow past a
certain point each second so now there's
time in this so if we add a time
measurement into that animation what you
could do if you wanted to is you could
count all the units of charge that flow
out of the picture or into the picture
and after you've counted a certain
amount over a certain period of time you
could come up with some kind of
calculation for how much charge went
through every certain period of time so
that would look like this for us we can
turn this into an equation and say that
current I is equal to Q which is the
charge divided by T which is the time
and the units of these properties would
be amps for current coulombs for charge
and seconds for time so this is usually
the way you'll see this equation
arranged because scientists like to have
equations where everything is all in one
line it just looks more presentable and
is usually easier to type and so
rearranging the equation I equals Q over
T would give you Q equals I times T it's
just a simple algebraic rearrangement it
is in fact the same equation as the one
you see above but that one in yellow is
the one that you'll typically see most
often so Q equals I times T is gonna be
the key to solving our an i-phone
question or our cell phone charging
question how do we keep our phones
charged more efficiently or more often
or more frequently so before we get to
that piece of advice here's a sample
calculation just to show you basically
how to use this formula that we just
learned and it says a light bulb has 40
coulombs of charge flow through it over
a timespan of two minutes
how much electric current is flowing
through the bulb so let's identify the
knowns and the unknowns in this question
the knowns are the charge because they
tell us that there's 40 coulombs of
charge we also know that the time is a
known quantity because they say this
happens over a timespan of two minutes
so we know charge we know time and the
unknown that they ask us about is how
much electric current is flowing through
the bulb so current is I that's the
thing we're gonna be solving for time is
T and we're given that
and coulombs of charge is Q so we know
two things and we're looking for a third
so that's typically where we say okay
what equation do we need and that's
gonna be the one that we just talked
about today Q equals I times T now it's
not really set up correctly to solve for
I at this moment it's set up for Q so we
have to rearrange this equation by
dividing both sides by T and then
canceling out the T's on the right would
give us this version of the equation Q
over T equals I and this happened just
coincidentally to be the first version
of it that I showed you
but again the top version is what you'll
see most frequently so we turn it into
this version and now we can plug in our
variables because now we're actually set
up to solve for the thing we're being
asked for so what is Q Q as a reminder
is 40 clumps because that was what was
given to us in the problem and the
amount of time listed for 40 coulombs to
pass through that light bulb was two
minutes but two minutes isn't set up to
be the base unit of time it's like a
different unit of time than what we
consider to be the base unit of seconds
it's in minutes right now so let's
change the minutes into seconds by
converting minutes to seconds by
multiplying by 60 because there are 60
seconds in every minute so multiplying
the number two by the number 60 for the
60 seconds per minute gives us a new
version of time where it's listed as the
same amount of time but listed in
seconds instead of minutes so now that
two minutes we have converted into
seconds and now the calculation goes
like this forty coulombs divided by 120
seconds will equal the amount of current
flow that we have in that light bulb so
what is 40 divided by 120 well either in
your head or in your calculator you type
in those numbers and you get 0.3 amps so
that would be your final answer and you
can't forget the unit amps is of course
the unit of current flow if we had been
instead solving this equation for T or
for Q you would have needed the unit s
for seconds or perhaps the unit C
coulombs for the charge so how do we
know how to properly rearrange this
formula well hopefully you develop
enough algebra skills that you can do it
on your own without something like this
but if you're new to this perhaps you
can just kind of get used to using the
formula triangle for Q equals I times T
it's set up like this and you'll notice
if I had taken my thumb or another
finger and blocked out the thing I was
solving for which was I in that formula
what you would get is Q over T and that
looks like the version of the equation
that gave you over yonder so use that
formula if you want is kind of like
training wheels but eventually you will
want to have enough algebra skills the
you can actually solve for that on your
own without a formula triangle so now
that we understand the connection
between charge Q current I and time T we
perhaps can understand charging our
phone a little bit easier and so what I
want to recommend is that if you often
find yourself with a dying phone or iPad
or something that just like never really
seems to get you through the day you
might want to go in Amazon or go to Best
Buy or something and pick up one of
these things these are called external
batteries or external chargers and
they're about the size of a wallet or a
smartphone and all they do is literally
store charge they store built-up
electrons which through a wire can go
into your device whatever it is and
simply charge it almost like you're
plugging it into a wall or a computer
and these will last you a couple hours
and in fact what they rate themselves
and in the unit that they use to
describe how much charge can be held you
can see in this top model up above me
the it's pretty cool actually the solar
powered one it lists a unit of 20,000
milliamp hours so what is a milliamp
hour it's like a unit of time well it's
actually a measurement of charge believe
it or not and it's because milliamps is
a unit of current so that's I and ours
is using is a unit of time so that's T
so that's I times T's or does that equal
that equals Q so milliamp hours is
actually unit of charge believe it or
not so anyways I recommend getting one
of these devices you just want to make
sure that it has enough milliamp hours
to be able to supply you with lots of
milliamps of current for as many hours
as possible so the higher the number the
better it is and the more you're gonna
pay as a result so do your shopping
wisely and see if it helps you and
hopefully Q equals IT will help you in
your physics class as well see in the
next video
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