Circuit electricity
Download
1 / 33

Circuit electricity - PowerPoint PPT Presentation


  • 84 Views
  • Uploaded on

Circuit electricity. Atomic structure. Atoms are composed of protons (+), electrons (-) and neutrons. The nucleus contains the protons and neutrons and the electrons surround the nucleus. Atomic structure.

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'Circuit electricity' - cerise


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

Circuit electricity

Atomic structure

Atoms are composed of protons (+), electrons (-) and neutrons. The nucleus contains the protons and neutrons and the electrons surround the nucleus.


Circuit electricity

Atomic structure

The outer layer of electrons in a metal is incomplete which allows them to pass from atom to atom


Circuit electricity

Atomic structure

Because electrons can pass from atom to atom. charge can pass through a conducting material such as a metal.

Metals are conductors


Circuit electricity

Atomic structure

Some materials such as rubber and plastic have complete outer layers of electrons so they cannot pass from atom to atom. Charge cannot pass through these materials.

These are called Insulators


Current
Current

Because it is the electrons which move from atom to atom in reality negative charge flows from negative to positive.

This has the same effect as positive charge moving from positive to negative

Conventional current flows from positive to negative


Circuit electricity

The Ampere (Named after Andre Marie Ampere)

The Ampere is a measure of how much electrical current is flowing and is measured in units of amps

QI = ---- t

I = amps Q = charge (in coulombs)

and t = time ( in seconds)


Circuit electricity

Potential Difference or Voltage

Alessandro Volta

Potential difference, or voltage, is the electrical potential energy per coulomb of charge.

EV = ----Q

V = voltage E = energy in Joules Q = charge (in coulombs)


Circuit electricity

Resistance

Georg Ohm

Resistance is a measure of opposition to the flow of charge and is measured in ohms ()

VI = ---- R

I = current V = voltage R = resistance in ohms


Ohms law three versions
Ohms Law (three versions)

VI = ---- R

V = IR

VR = ----I


Electrical power
Electrical Power

Power is the rate of using energy in joules per second

P = E

t

or E = Pxt


Electrical power1
Electrical Power

From previous slides we know that

EV = ---- Q

QI = ---- t

and


Electrical power2
Electrical Power

Combine the two and cancel the Q from each

EV = ---- Q

QI = ---- t

X

Leaving E/t so electrical power is P = V x I


Electrical power equation variations
Electrical Power Equation variations

P = V x I

P = I2R

P = V2/R

These were obtained by using Ohm’s law to substitute for V and I


Kirchoff s laws
Kirchoff’s Laws

Kirchoff’s first Law

The total current flowing into a junction is the total current flowing out of the circuit

I2

I1

I3

I1 = I2 + I3


Kirchoff s second law
Kirchoff’s Second Law

1. The sum of the potential

differences around an electrical

circuit equals the supply

voltage.


Resistors in series
Resistors in series

The total resistance is found by simply adding the resistance of each

R1 + R2 +R3etc


Resistors in series1
Resistors in series

The supply voltage (pd) is shared across the resistors. The voltage across each depends on the resistance of each


Resistors in series2

The current in a series circuit is the same all the way round the circuit

(as per Kirchoff’s first Law). Current flowing into the resistor is the same as the current flowing out of the resistor)

Resistors in series


Resistors in parallel
Resistors in parallel round the circuit

The total resistance is calculated as below


Resistors in parallel1
Resistors in parallel round the circuit

  • The current in a parallel circuit is shared between each resistor. (The amount in each depends on the resistance)


Resistors in parallel2
Resistors in parallel round the circuit

  • The supply voltage (pd) across each resistor is the same as the supply voltage


Combined resistors
Combined resistors round the circuit

To calculate the total resistance of the circuit calculate the parallel set first and treat it as a single resistor in series with the other resistor


Example
Example round the circuit

From the following diagram determine:

a) Total resistance.

b) Total (supply) current.

c) Voltage across each resistor.

d) Power loss in resistor R1.

R1 = 50Ω, R2 = 100Ωand supply voltage = 12V.


Example1
Example round the circuit

Total resistance = R1 + R2 =150Ω

Total (supply) current V/I = 12/150 =0.08 amps.

Voltage across R1 = 50 x 0.08 = 4 volts

Voltage across R2 = 100 x 0.08 = 8 volts

Power loss in R1 = V x I = 4 x 0.08 = 0.32 Watts

R1 = 50Ω, R2 = 100Ωand supply voltage = 12V.


Example2
Example round the circuit

From the following diagram determine:

a) Total resistance.

b) Total (supply) current.

c) Current through each resistor.

R1 100Ω, R2 = 1kΩand supply voltage = 12V.


Example3
Example round the circuit

1/Total resistance = 1/100 +1/1000.= 10/1000 + 1/1000 = 11/1000

Total resistance = 1000/11 =90.9Ω


Example4
Example round the circuit

Total current = V/R = 12/90.9 = 0.132 amps

Current through R1, V/R1 = 12/100 = 0.12 amps

Current through R2, V/R2 = 12/1000 = 0.012 amps


Example5
Example round the circuit

From the diagram below, determine:

a) The total resistance, and the supply current.

b) The voltage across the R1 resistor.

c) The current through R2 , and the power dissipated in it.

R1 = 200Ω R2 and R3 are both 100Ω and the supply voltage is 12 volts


Example6
Example round the circuit

Resistance of the parallel resistors

1/total = 1/100 +1/100

=2/100

Total resistance = 100/2

= 50Ω

Total resistance in circuit = 200+50 = 250Ω

Current = V/R

=12/250

=0.048 amps


Example7
Example round the circuit

Voltage across R1

I x R

=0.048 x 200

= 9.6 volts


Example8
Example round the circuit

Voltage across R1 & R2

V = I x R

0.048 x 50

= 2.4 volts

Current through R2

I = V/R

=2.4/100

=0.024amps


Example9
Example round the circuit

Power dissipated

P = V x I

2.4 x 0.024

= 0.058 watts