Electric circuits

ELECTRIC CIRCUITSGRADE 10

Compiled byMESOLO M.P

wiring

battery

voltmeter

ammeter

resistance

capacitor

+ -

A

V

junction

terminal

AC generator

Variableresistance

Variablecapacitor

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Potential difference and emfThe potential difference across the terminals of a battery when it is not in a complete circuit is the electromotive force (emf) measured in volts (V).

The potential difference across the terminals of a battery when it is in a complete circuit is the terminal potential difference measured in volts (V).

Voltage is a measure of the work required/done to move a certain amount of charge and is equivalent to J·C−1.

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CurrentCurrent is the rate at which charge moves/flows and is measured in amperes (A) which is equivalent to C·s−1.Conventional current flows from the positive terminal of a battery, through a circuit, to the negative terminal.We use the symbol I to represent current. We can calculate current using:

𝐼=𝑄Δ𝑡

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Measuring current and potential difference

Voltmeters measure potential difference (voltage) and must be connected in parallel.Ammeters measure current and must be connected in series.

Photo by Ufbastel on wikipediaPhoto by Christos vittoratos on wikipedia

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ResistanceResistance is a measure of how much work must be done for charge to flow through a circuitelement and is measured in ohms (Ω) and is equivalent to V·A−1.Resistance of circuit elements is related to the material from which they are made as well as the physical characteristics of length and cross-sectional area.

Photo by Oskay on Flickr

Resistors in series circuitsCurrent is constant through resistors in series and they are called voltage dividers as the sum of the voltages is equal to the voltage across the entire set of resistors.The total resistance of resistors in series is the sum of the individual resistances.

𝑅𝑆=𝑅1+𝑅2+𝑅3+ ... 𝑉 battery=𝑉 1+𝑉 2+𝑉 3+.. .

There are many circuits in which more than one device is connected toa voltage source.

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

SIRRRIIRIRVVV 212121

321 RRRRSSeries resistors

Resistors in parallel circuitsVoltage is constant across resistors in parallel and they are called current divides because the sum of the current through each is the same as the total current through the circuit configuration.

The total resistance of resistors in parallel is calculated by using:

𝑉 battery=𝑉 1=𝑉 2=𝑉 3=.. .

1𝑅𝑃

=1𝑅1

+1𝑅2

+1𝑅3

+.. .

SERIES CIRCUIT:

-There is only ONE PATH for the electrons to take between any two points in the circuit.*There will be no alternative route.

-Has more than one RESISTOR. Since there is only one path for the current to travel, the current through each of the resistors is the same.*Resistors are components that are used to control the amount of current flowing in a circuit.

PARALLEL CIRCUITS:

-Two or more components are connected between the same two points.

- Has more than one resistor and gets its name form having multiple paths to move along.* Charges can move through any of the several paths. If one of the items in the circuit is broken, then no charge will move through that path. But other paths will continue to have charges flow through them.

20.7 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 eitherresistor alone.

20.7 Parallel Wiring

SERIES CIRCUIT PARALLEL CIRCUIT

DESCRIPTION If one the items in the circuit is broken, then no charge will move through the circuit because there is only ONE PATH.

If one of the items in the circuit is broken then no charge will move through that path, but OTHER PATHS will continue to have charges flow through them.

RESISTOR As more resistors are added, the overall current in the circuit decreases.

As the number of resistors increases, the overall current also increases.

RECAP!

EQUIVALENT RESISTANCE-Is the amount of resistance that a single resistor would need in order to equal the overall effect of the collection of resistors that are present in the circuit.

RESISTORS IN SERIES:Two resistances are connected in series if all the current from one resistor must flow through the second; there is no alternative route.

Equivalent resistance:

From conservation of charge: I1 = I2 = I

where I is the current through the combination.

From conservation of energy: V1 + V2 = V

where V is the potential difference across both resistors.The two resistors can be replaced by a single resistor with the equivalent resistance

For more than two resistors, Req = R1 + R2 + R3 + ...

RESISTORS IN PARALLEL: - Two resistors are connected in parallel if they are joined at both ends such that the potential difference across both resistors is the same. The current splits, flows through the two resistors, then comes back together with no alternate path.

Equivalent resistance:

From conservation of charge: I1 + I2 = I

From conservation of energy: V1 = V2 = V

The two resistors can be replaced by a single resistor with the equivalent resistance Req:

For more than two resistors:

RECAP!

SERIES CIRCUIT PARALLEL CIRCUIT

The total resistance of the circuit, also called effective resistance is equal to the sum of the individual resistances.

The inverse of the total resistance of the circuit, is equal to the sum of the inverses of the individual resistances.

R = R1 + R2 + R3 + … 1/R = 1/R1 + 1/R2 + 1/R3 + …

ELECTRIC POWER AND ENERGY

Electric Power:- Represents the rate at which energy is converted from the electrical energy of the moving charges to some other form.- The SI unit of power is watt.

Electric Energy:-Represents the presence and flow of an electric charge. The energy portion of electricity is found in a variety of phenomena such as static electricity, electromagnetic fields and lightning.-Consumption of electrical energy is measured by Watt x Hour (Wxh)* 1Wh = 3600 joule = 859.8 calorie

REFERENCES

• The slides were compiled by Mesolo MP with the slides from slide share, the authours and links are:

• http://www.slideshare.net/fourangela/series-parallel-11767502?qid=2fc1a7d9-1e75-4571-ab7f-5a3d8c903066&v=qf1&b=&from_search=9

• http://www.slideshare.net/Siyavula_Education/electric-circuits-grade-10

• http://www.slideshare.net/wsautter/electrical-circuits.Nisa Sho on Dec 31, 2008

• http://www.slideshare.net/Wansyi/electricityelectronics-ch20-presentation. Walt Sautter, retired at Middlesex County College on Feb 12, 2010