FISIKA Kelas 12 - Hukum Coulomb & Medan Listrik | GIA Academy

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Hello friends, welcome back

to the Gia Academy YouTube channel. I hope

you are always healthy and keep up the

spirit. Have

you ever seen lightning? The

following image is lightning that has

occurred and was successfully captured by a

camera. Well, friends, lightning is

one of the electrical phenomena, especially

static electricity. Lightning can occur

because electrons at the bottom of the cloud

are attracted by protons on land.

Of course, you still remember. What is

the difference between protons and electrons? Why

can they attract each other? Is

there a connection with the concept of

electric charge? Well, so that the question is

answered, we will discuss this material

completely in this video.

So, in this video, we will learn

about Coulomb's law and electric fields.

Keep watching the video,

friends. Previously, we

learned about the concept of electric charge.

There are two types of electric charge, namely

positive electric charge called

protons and negative electric charge

called electrons. 2 similar charges

when brought close together will repel each other,

while those that are not the same when

brought close together will attract each other. Now,

friends, do you understand? Why do protons and

electrons attract each other? The

interaction of attraction or

repulsion that occurs in several

electrically charged objects that are brought close together is

caused by electrostatic forces

which are often called electrostatic forces. coulomb

magnitude of electrostatic force This was

first observed by Charles Augustin

Deculom Kulon's experiment using a

torsion balance he succeeded in investigating the

relationship between electrostatic force

with the charge and distance of each

charged object Kulon concluded that the

electrostatic force between two

electric charges is directly proportional to the magnitude of

each charge and

inversely proportional to the square of the distance between the

two charges this column conclusion is

what is finally known as Coulomb's law

Coulomb's law mathematically can be

written as f = k times Q1 times Q2

divided by r squared k =

1/4 PF silon 0 so that f is also equal

to

1/4 pfclon 0 times Q1 times Q2 divided

by r squared with F coulomb force

unit neutron k column constant

value is 9 * 10 ^ 9 Newton meters squared

per column squared Q1 and Q2 the charge of the object

unit is culot R the distance between the two charges is

meters and epilog zero the

electrical permittivity in a vacuum is

8.85 times 10 to the power of negative 12 columns

squared per Newton meters squared

if the space between the charges is not a

vacuum but a medium other then the

permittivity value becomes larger and

is expressed by epsilon greater

than epsilon 0 or epsilon is equal to

epsilon R multiplied by epsilon 0 epsilon

electrical permittivity in medium

epsilon 0 electrical permittivity in

vacuum epsilon R

dielectric constant or relative permittivity the

magnitude of the Coulomb force in a medium that is

not air is expressed by the equation

FR = k times Q1 times Q2 divided by

epsilon R * r² with FR the coulomb force

in the medium its unit is Newton the

coulomb force is a vector quantity

so that if there are several

electric charges in one room then the resultant

coulomb force can be summed

vectorially in this video we will discuss the

magnitude and direction of the Coulomb force in

several charge arrangements

first we look first at the

Coulomb force on two similar and

dissimilar charges on two similar charges

for example positive charge Q1 which is separated by a

distance of R with positive charge Q2 then the

column force that occurs is F12 and

f21 F12 is the Coulomb force on charge

Q1 due to charge Q2 and f21 is the

Coulomb force on charge Q2 due charge Q1

because charge Q2 repels charge Q1 then

charge Q1 gets a repulsion force of

F12 to the left charge Q1 also repels

charge Q2 so that f21 is directed to the right

both charges repel each other

while in two unlike charges

for example negative charge Q1 and

positive charge Q2 which are separated by a distance of R F12 is

directed to the right because charge Q2

attracts charge Q1 and f21 is directed to

the left because charge Q1 attracts charge Q2

both charges attract each other

This concept needs to be understood by friends Yes because it is

very important to determine the

coulomb force due to the interaction of more than two

charges based on Coulomb's law large

F12 is equal to f21 is also equal to K

times Q1 times Q2 divided by r

squared

then we see the magnitude and direction of the

Coulomb force on three unlike electric charges

located in a line

positive charge Q1 is located at point a

and negative charge Q2 is located at

point B at point c which is

between them is placed

positive charge q3 with a distance R1 from charge

Q1 and R2 from charge Q2 then to

determine the magnitude and direction of the coulomb force

that occurs on charge q3 namely F3

we Draw the Coulomb force f31 and f32

because the charge Q1 repels the charge q3 then

f31 is directed to the right f32 is also directed to

the right because the charge Q2 attracts the charge q3

F3 is in the same direction as f32 so that the magnitude of

F3 =

f31 + f32 is also the same as the triangle

q1 / r 1 squared plus the triangle

q2 / r2² in the same way we

can also determine the magnitude and direction of the

Coulomb force on three similar electric charges

located in a line well

How to determine the magnitude and

direction of the Coulomb force on three unlike charges

located at the vertex of the

triangle is the same as the three charges

located in a line first

we describe the column forces

acting on the charge that we will

determine the value of the Coulomb force 3 unlike charges are

arranged as follows

we will determine the value of F3 the

Coulomb force that occurs on the charge q3 F3

is the resultant of f31 and f32

f31 is directed away from the charge Q1 because the

charge q3 is similar to Q1

f32 is directed towards the charge Q2 because

the charge q3 is not similar to Q2

f31 and f32 form an angle of Alpha

so that F3 = root of f31 squared

plus

f32² + 2 times f31 times f320

lastly how to determine the magnitude and direction of the

Coulomb force on four unlike charges

located at the corner points of the

square we will determine the magnitude and

direction of the Coulomb force on charge Q1, namely

F1 first we describe all the

Coulomb forces acting on charge Q1

including first

F12 = leg 1

q2 / r² the direction is away from charge Q2 second

f13 =

kq1 q3 / r

√2 squared the direction is approaching charge

q3 third

f14 = leg 1 q4 per r squared the direction

is away from charge q4 next we

determine the resultant of F12 and f14, namely

f24 the direction is away from charge Q1

f24 = root of

F12 squared plus

f14²

f13 is in line with f24 but in the opposite

direction so that we get F1 =

f13 minus f24 until here

friends understand yes

next we will discuss about electric fields electric

fields are

areas around electric charges that are

still influenced by the electric force of the

charge electric fields

are described by electric force lines

with the direction outward from the

positive charge towards the negative charge Well

friends to find out the size of

how strong an electric field is we

know the term electric field strength

white electric field is often also called

electric field intensity to

find out the magnitude of the electric field strength

produced by a

source charge we have to place a test charge

around the source charge the

test charge produces an electric field that is much

smaller than the source charge that

will be calculated the field strength The test charge

used is always positively charged the

magnitude of the electric field strength

produced by the source charge is

defined as the quotient between the

coulomb force acting on the

test charge and the magnitude of the test charge

mathematically the electric field strength

can be calculated with the equation e = f

/ Q2 is the same as K times Q1 divided by

r squared with e the electric field strength

unit is Newton per column F the

coulomb force acting on the test charge

the unit is Newton k the column constant is

9 times 10 to the power of 9 Newton

meters squared per column squared Q1

source charge Q2 test charge both

in column units and R the distance between the

test charge and the source charge the unit is meters

to determine the magnitude of the electric field strength

at a point then the point is always

considered positively charged we suppose the

point that we will calculate the electric field strength

is point c if point c

is located between two unlike charges

for example positive charge Q1 and

negative charge Q2 then point c

is influenced by two electric fields namely

electric field E1 due to positive charge

Q1 and electric field E2 due to

negative charge Q2 S1 direction is to the right because

it is away from positive charge Q1 and e2

direction is also to the right because it is towards

negative charge Q2 S1 is in the same direction as E2

so that the total electric field strength

at point c is

1 plus E2 is also the same as

kq1/r 1 squared plus k q

2/r2² with R1 Distance of point c from

charge Q1 and R2 Distance of point c from

charge Q2 then if point c

is located between two similar charges

point c is also influenced by two

electric fields only the direction of both is

opposite E1 direction is to the right because it

is away from positive charge Q1 while E2

direction is to the left because it is away from

positive charge Q2 so the total electric field strength

at point c is EC = E1 - E2

finally if point c is located at

one of the corner points of the triangle point c

which has positive charge is also influenced

by electric field E1 and electric field

E2 electric field E1 away from

positive charge Q1 and electric field E2 towards

negative charge Q2 both form an

angle of Alpha so that the

total electric field strength at point c is EC =

√ from e1² + e2² + 2 * E1 times E2 cos

Alfa until here friends can

understand

so that friends understand more Let's

solve the following example questions the

first question is known charge Q1 =

-9 micro Coulomb and charge Q2 = + 6

micro Coulomb both of them we convert to

column units distance R = 3 m and k = 9

times 10 to the power of 9 Newton meters squared

per column squared we are asked

to determine the magnitude of the coulomb force

experienced by both charges we can

solve this problem by

using Coulomb's law f = k Q1

q2 / r² remember to complete

the calculation yes we do not need to

enter the charge sign we enter

all the values ​​F = 9 times 10 to the power of 9

times 9 times 10 to the power of negative 6

times 6 times 10 to the power of negative 6

divided by three squared we do

the calculation until we get F =

54 times 10 to the power of negative 3 is also equal

to

0.054 n so the answer is B the

second question is known two charges a and b are

similar and repel with a force of

F we are asked to determine the magnitude of the

coulomb force after charge a is enlarged

twice as originally charge B is enlarged 3

times as originally and the distance between the two is

enlarged twice as originally to make it

easier for us to calculate it we

use the Comparison of the final coulomb force

with the initial coulomb force F accent

per F = accent feet qb accent per R accent

squared divided by aqb feet per r

squared k we can cross out so that F

accent per F becomes

qa'/qa * qb accent per q b * r/ r accent

squared we enter the value then

we Simplify we get the magnitude of the

final coulomb force after the charge and

distance are changed is

3/2 times the initial coulomb force so the

correct answer is B the

next question two electric charges

a and b each positive 4 micro

Coulombs and positive 9 micro Coulombs

are at a distance of 20 cm between the two

charges is placed charge c which

is positive 5 micro Coulombs we

are asked to determine the position of charge C so that

charge c does not experience coulomb force

to make it easier for us to

solve this problem we describe the

arrangement of our three charges Suppose

the distance charge C from charge a is X

and the distance of charge C from charge b is

20 less X then we describe the

column forces acting on charge

C namely

fca and FCB fca direction to the right because

charge C is repelled by charge a FCB

direction to the left because charge C is also

repelled by charge B because fca is in the opposite

direction to FCB then FC =

fca - FCB FC = 0 so that

kqc

qb / rcb² =

kqc q a per r ca² k and QC can be

crossed out we get the equation

rca per rcb squared =

qa / qb we enter the value we

get x = 8 cm and 20 less x = 12 cm

this means charge C is located 8 cm from

charge A or 12 cm from charge B

the answer is B the

fourth question is given an arrangement of three

charges Q1 Q2 and q3 which are at

the ends of a right triangle ABC

as in the picture length AB = BC = 30

cm we are asked to determine the resultant

Coulomb force on charge Q1 first

we describe the Column forces on

charge Q1 due to charge Q2 and q3 F12

away from charge Q2 and f13 away from

charge q3 We determine the magnitude of

each using

Coulomb's law we get F12 = 3 Newton and

f13 = 4 n then to determine the

resultant Coulomb force on charge Q1

we use the equation F1 = root of

F12 squared plus

f13 squared plus

2f12 f13 cos Alfa Alfa = 90° so that

cos Alfa = 0 then F1 =

√from

f12² + f13 squared we enter

the value we get f1 = 5 n so the

correct answer is B the

last question two separate electric charges

as in the picture point C

is between the two charges 10

cm from a if qa = 3 micro Coulomb and

qb =

-4 micro Coulomb we are asked to determine the

magnitude of the electric field strength at point c

due to the influence of charge A and charge B

first we determine the direction of the two electric

fields acting at point c the

electric field due to charge a is ea the

direction is away from charge a which is a

positive charge while the electric field

due to charge B is EB the direction is towards

charge B which is negative charge

because Ea and EB are in the same direction, then the total electric field strength

at point c is EC = ea

plus EB, we use the

electric field strength equation, we enter the value and

we do the calculation, we get the

total electric field strength at point c

of 36 times 10 to the power of 5

n / cm The answer is d

Okay friends, that's

our discussion about Coulomb's law and

electric fields Don't forget to keep watching the

latest videos on our channel,

see you in the next video

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