APPLYING OHM'S LAW

ELECTRICITY

is the set of physical
phenomena associated
with the presence and
motion of matter that
has a property of
electric charge.

It was discovered about
600 BC, THALES, a
Greek philosopher and
scientist.

Came from the Greek
word “Electron”
meaning “AMBER”

is the flow of electrical
power or charge.

Charges are:

• Positive (proton)
• Negative (electron)
• Neutral (neutron)

OHM’S LAW

•

The current flowing

through a circuit is directly proportional to the

potential difference and inversely proportional to the resistance of the

circuit. The first part of the law may be represented as

I

(current)

∝

V

(potential difference). The second part may be expressed as

I

∝

1/R.

Algebraically, Ohm’s law is

I = V/R

•

Where

I

, the rate of flow of electric charge referred to as

current

, is

measured in amperes (A).The

ammeter

is the instrument used to measure

current. The potential difference

V

is in

volts

(V) and the instrument that

directly measures this is the

voltmeter

. R, the

resistance

to the flow of

electrons by the conductor, is given in ohms (Ω). one way of directly

measuring electrical resistance is using

ohmmeter

.

RESISTANCE

•

Resistance

is a measure of the opposition to

current flow in an electrical circuit.

•

Resistance is measured in ohms, symbolized

by the Greek letter omega (Ω). Ohms are

named after

Georg Simon Ohm

(1784

-

1854), a

German physicist who studied the relationship

between voltage, current and resistance. He is

credited for formulating Ohm's Law.

VOLTAGE

is

the

pressure from
an

electrical

circuit's
power source
that

pushes

charged
electrons
(current)
through

a

conducting
loop,
enabling
them

todo

work such as
illuminating a
light.

The

man

to

first

discover

voltage

was

Italian
Physicist
Alessandro
Volta

was

also

credited

with

creating

the

first

electric

battery,
called

the

Voltaic

Pile,

which allowed
scientists

of

the

time

to

create

a

steady flow of
electrons.

In

the

Philippines the
supply
voltage
is 220V. If the
appliance is a
single voltage
rated
appliance,

it

will

need

to

operate at the
same voltage
as the supply
voltage of the
country

i.e.

220V.

CURRENT

➢

Rate of flow of charge

➢

Amount of charge per unit time that crosses one

point

➢The ampere is named for French physicist and

mathematician André-Marie Ampère (1775–1836),
who studied electromagnetism and laid the
foundation of electrodynamics. In recognition of
Ampère's contributions to the creation of modern
electrical science, an international convention,
signed at the 1881 International Exposition of
Electricity, established the ampere as a standard
unit of electrical measurement for electric current.

PROBLEM SOLVING

•

What is the potential difference in an electric circuit with a current of 58 amperes

and a resistance of 9.0 ohms?

• Find the current I through a resistor of resistance R = 22 Ω if the voltage across the

resistor is 180 V.

• How much current would flow through a circuit that has 1000 Ohms of resistance

if powered by 1.5 volts?

• What is the amount of current flows in a 220 V wire with a resistance of 60 ohms?

ELECTRIC CIRCUIT

is an interconnection of electrical
components or a model of such
an interconnection, consisting of
electrical elements. An electrical
circuit is a network consisting of a
closed loop, giving a return path

for the current.

includes a device that gives

energy to the charged particles
constituting the current, such as a
battery or a generator; devices
that use current, such as lamps,

electric motors, or computers; and

the connecting wires or

transmission lines.

5 MAIN TYPES OF ELECTRIC CIRCUIT

• Closed circuits
• Open circuits
• Short circuits
• Series circuits
• Parallel circuits

CLOSED CIRCUIT & OPEN CIRCUIT

• An open circuit is one where the

continuity has been broken by an
interruption in the path for current to
flow.

• A closed circuit is one that is

complete, with good continuity
throughout.

• A device designed to open or close a

circuit under controlled conditions is
called a switch.

SHORT CIRCUIT

• is an electrical circuit that allows a

current to travel along an unintended
path with no or very low electrical
impedance.

• This results in an excessive current

flowing through the circuit.

• The opposite of a short circuit is an

"open circuit", which is an infinite
resistance between two nodes.

SERIES AND

PARALLEL CIRCUIT

• In a series circuit, the same

amount of current flows
through all the components
placed in it.

• Parallel circuits, the

components are placed in
parallel with each other due
to which the circuit splits the
current flow.

RULES FOR RESISTANCE IN SERIES ARE AS

FOLLOWS:

GIVEN:

R

1 = 20

R4 = 75

R2 =10

R 5 = 55

R3 = 5

VT= 220

•

Example: Let us assume that you have five

appliances connected in series as in the figure.

The refrigerator has a resistance of 20 Ω; the

TV set, 10 Ω; the radio, 5 Ω; the flat iron, 75 Ω;

and the electric stove, 55 Ω. If the circuit is

connected to a direct current of 220 volts,

what is

•

a. the total resistance in the circuit?

•

b. the total current?

•

c. the voltage across each appliance?

1. For the following circuit:
Find the total resistance
Find the current i
Find the voltage accross the 10Ω
resistor

A refrigerator, TV set, radio, flat iron, and electric stove have a
resistance of 25 Ω, 15 Ω, 50 Ω, 70 Ω, 50 Ω, respectively. If it is
connected in series circuit and the
circuit is connected to a direct current of 220 volts, what is the:
A.Total resistance in the circuit?
B. Voltage drop in each appliance?
C.Current used by each appliance, in respective order?
D.Total current?

RULES FOR RESISTANCE IN PARALLEL ARE AS

FOLLOWS:

•

In

the

figure,

the

refrigerator,

TV

set,

radio,

flat

iron,

and

electric

stove

have

a

resistance

of

20

Ω,

10

Ω,

5

Ω,

75

Ω,

55

Ω,

respectively

.

If

the

circuit

is

connected

to

a

direct

current

of

220

volts,

what

is

the

•

a

.

total

resistance

in

the

circuit?

•

b

.

voltage

drop

in

each

appliance?

•

c

.

current

used

by

each

appliance?

•

d

.

total

current?

•

A refrigerator, TV set, radio, flat iron, and electric stove

have a resistance of 2

Ω

, 10

Ω

, 15

Ω

, 25

Ω

, 5

Ω

,

respectively. If it is connected in

parallel

circuit and the

circuit is connected to a direct current of 220 volts, what is

the:

A.

Total resistance in the circuit?

B.

Voltage drop in each appliance?

C.

Current used by each appliance, in respective order?

D.

Total current?

• For one, the total resistance

of a Parallel Circuit is NOT
equal to the sum of the
resistors (like in a series
circuit). The total resistance
in a parallel circuit is always
less than any of the branch
resistances. Adding more
parallel resistances to the
paths causes the total
resistance in the circuit to
decrease.

A.

Total resistance in the circuit?

B.

Voltage drop in each

appliance?

C.

Current used by each

appliance, in respective

order?

D.

Total current?

ACTIVITY

•

1. What is the voltage if a resistance of 25 Ω produces a current of 250 amperes?

•

2. What is the current produced by a voltage of 240 V through a resistance of 0.2

Ω?

•

3. What voltage is necessary to produce a current of 200 amperes through a

resistance of 100 Ω?

•

4. What resistance would produce a current of 120 amps from a 6

-

V battery?

•

5. What is the current produced by a 9

-

V battery flowing through a resistance of

200 Ω?