Physics Lesson - Charge and Current (Q=It)

Summary

This 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

00:00

🔋 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.

05:02

🔌 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.

Keywords

💡Interconnectedness

Interconnectedness refers to the state of being connected or linked together, especially in a complex way. In the context of the video, it describes the reliance on technology, such as smartphones, to stay connected with the world around us. The script mentions the feeling of disconnection when one wakes up to find their phone is not charged, illustrating the deep integration of technology in our daily lives.

💡First World Problem

A 'First World Problem' is a term used to describe a minor inconvenience experienced by people in economically developed countries, which is often trivial compared to the more serious issues faced by people in less developed areas. The script humorously acknowledges that the frustration of a dead phone battery is a relatively minor issue in the grand scheme of global problems.

💡Electrons

Electrons are subatomic particles that carry a negative electric charge. They are fundamental to understanding electrical current and are mentioned in the script as the basic units of charge that flow from a charging device into a phone, thereby charging it. The script simplifies the concept of phone charging by focusing on the flow of electrons.

💡Ohm's Law

Ohm's Law is a fundamental principle in electrical engineering that relates voltage (V), current (I), and resistance (R) in an electrical circuit. It is expressed as I = V/R. The video uses Ohm's Law to explain how the voltage and resistance interact to determine the flow of current, which is crucial for understanding how a phone charges.

💡Voltage

Voltage, measured in volts, is the electrical force or pressure that pushes electrons through a conductor, such as a wire. The script uses the concept of voltage to explain how doubling the voltage can double the current, which is an example of how changing voltage can affect the charging process.

💡Resistance

Resistance is a property of materials that opposes the flow of electric current. It is measured in ohms. In the script, resistance is described as an internal factor that tries to block the flow of electrons, and it is part of the equation in Ohm's Law that determines the amount of current flow.

💡Current

Electric current is the flow of electric charge, typically measured in amperes (amps). The script explains that current is the amount of charge (in coulombs) flowing past a certain point per unit time (in seconds), which is a key concept in understanding how quickly a phone charges.

💡Coulombs

A coulomb is the unit of electric charge, named after Charles-Augustin de Coulomb. The script uses coulombs to quantify the amount of charge flowing through a device, such as a light bulb, to calculate the electric current using the formula I = Q/T.

💡External Battery

An external battery, also known as a power bank, is a portable device used to charge or power other devices, such as smartphones, when they are not connected to a wall outlet. The script recommends using an external battery to ensure phones stay charged throughout the day, highlighting its practical use in maintaining connectivity.

💡Milliamp Hours (mAh)

Milliamp hours is a unit of electric charge, equivalent to one thousandth of an ampere multiplied by one hour. It is used to express the capacity of batteries, including those in power banks. The script mentions that a higher mAh rating indicates a larger capacity to hold charge, which is important for choosing an effective external battery.

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