expt. 8 series and parallel circuits

8/17/2019 Expt. 8 Series and Parallel Circuits

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Electromotive Force and Current

In an electric circuit, an energy source and an energy consuming device

are connected by conducting wires through which electric charges move.


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Within a battery, a chemical reaction occurs that transfers electrons from

one terminal to another terminal.

The maximum potential difference across the terminals is called the

electromotive force (emf).


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The electric current is the amount of charge per unit time that passes

through a surface that is perpendicular to the motion of the charges.

t q I

One coulomb per second equals one ampere (A).


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If the charges move around the circuit in the same direction at all times,

the current is said to be direct current (dc).

If the charges move first one way and then the opposite way, the current is

said to be alternating current (ac).


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Conventional current is the hypothetical flow of positive charges that would

have the same effect in the circuit as the movement of negative charges that

actually does occur.


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Ohm’s Law

OHM’S LAW

The ratio V/I is a constant, where V is thevoltage applied across a piece of mateiral

and I is the current through the material:

SI Unit of Resistance: volt/ampere (V/A) = ohm (Ω)

IRV R I

V orconstant


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Ohm’s Law

To the extent that a wire or an electrical

device offers resistance to electrical flow,

it is called a resistor.


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The Measurement of Current and Voltage

An ammeter must be inserted into

a circuit so that the current passes

directly through it.


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Safety and the Physiological Effects of Current

To reduce the danger inherent in using circuits, proper electrical grounding

is necessary.


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Series Wiring

There are many circuits in which more than one device is connected to

a voltage source.

Series wiring means that the devices are connected in such a waythat there is the same electric current through each device.

i i i


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Series Wiring

S i Wi i


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Series Wiring

Personal electronic assistants.

P ll l Wi i


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Parallel Wiring

Parallel wiring means that the devices areconnected in such a way that the same

voltage is applied across each device.

When two resistors are connected in

parallel, each receives current from the

battery as if the other was not present.

Therefore the two resistors connected inparallel draw more current than does either

resistor alone.

P ll l Wi i


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Parallel Wiring

Parallel Wiring


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Parallel Wiring

The two parallel pipe sections are equivalent to a single pipe of the

same length and same total cross sectional area.

Parallel Wiring


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Parallel Wiring


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RESISTORS IN

SERIES

RESISTORS IN

PARALLEL

RT = R1 + R2 + … 1/RT = 1/R1 + 1/R2 + …

IT = I1 = I 2 IT = I1 + I 2

VT = V1 + V2 VT = V1 = V2


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Determination of Resistance

Color DigitBlack 0

Brown 1

Red 2

Orange 3

Yellow 4Green 5

Blue 6

Violet 7

Gray 8

White 9Gold +5%

Silver +10%

Colorless +20%

D AB C

10

___ __________

___ __________

___ __________

3

2

1

R

R

R


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Activity 1: Series Resistors

Voltage (V) Current (I)

R1

R2

Theoretical RT

Experimental RT

% Error


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...

...

...

21

21

21

V V V

I I I

R R R

ConnectionSeries

T

T

T

Activity 1: Series Resistors


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Activity 2: Parallel Resistors

Voltage (V) Current (I)

R1

R2

Theoretical RT

Experimental RT

% Error


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......

...111

21

21

21

V V V I I I

R R R

Connection Parallel

T

T

T

Activity 2: Parallel Resistors


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...

...

...

21

21

21

V V V

I I I

R R R

ConnectionSeries

T

T

T

......

...111

21

21

21

V V V I I I

R R R

Connection Parallel

T

T

T

Series and Parallel Resistors


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Activity 4: Combination of Cells

In Series In Parallel

Electromotive force of Cell (E)

Known Resistance (R)

Current (I)

Internal Resistance of Cell (r)

Activity 5: Parts of a Cells


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Activity 5: Parts of a Cells

expt. 8 series and parallel circuits

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