circuits and electrical diagrams · 2019. 8. 12. · the voltage across all elements in parallel is...

Circuits and

electrical diagrams

Circuits: a circular path through which electrons can flow.

In order for electrons to flow, they must have a path into the circuit and out of the circuit. (circular path)

A CLOSED circuit has a complete path (without breaks) allowing electrons to flow. (like a closed door)

An OPEN circuit has the flow interrupted by a break in the path of the electron flow. (like an open door)

5 amps

0 amps

A SHORT Circuit occurs when the electrons have a short cut that allows them to complete the circle without going through the intended path.

500+ amps

Note that without the resistor in the loop the current would flow un-restricted.

5 amps

A series of events is a bunch of things that happen

one after the other.

You get out of bedthen

You eat breakfastthen

you leave for school

A circuit has items such as resistors in series if the

current (electrons) flow from one into the next and then into the next (and so on).

Parallel events all happen at the same time, they

are like events on parallel lines.

your were eating breakfastwhile

Your brother was brushing his teethwhile

you were listening to music

A circuit has items such as resistors in parallel if the

current (electrons) flows through them all at the same time.

Series vs. ParallelOne path

All components have the

same current

More items increases

overall resistance.

Voltage can be different for

each item

Multiple paths

Current in each

component can vary

More items decreases

overall resistance.

Voltage across each item

is the same

video: How NOT to get shocked.

All circuits must have a resistor.

Current can never be allowed to flow around the circuit un-resisted.

Ohms Law I = V/R would suggest that an un-resisted circuit would have an infinitely high Current.

However: all conductors have some resistance, so we cannot actually make a completely un-resisted circuit.

The resistance of a wire depends on three things

• The material of the wire (gold, copper, iron)

• The size of the wire (14 gauge, 22 gauge, ) cross

sectional area.

• The length of the wire.

• (sometimes the temperature)

Drawing Circuits

Switches Battery

Light bulbResistor

or or

(closed) (open)

(one) (two)

AmmeterMeasures

amount of

current(Only in

series

circuits)

VoltmeterMeasures

the voltage

drop(Only in

parallel

circuits)

Volt meters are placed in parallel to the circuit.

Volt meters have very high resistance so that no current will flow through them.

Volt meters measure the drop (change) in voltage. V

Amp meters are placed in series with the circuit items.

Amp meters have very LOW resistance so that the current is unchanged by them.

Amp meters measure current going through them.(which is the same as the other items in series with it)

A

Virtual circuit making on the internet.

Click here

https://phet.colorado.edu/sims/html/circuit-construction-kit-dc/latest/circuit-construction-kit-dc_en.html

RS practice pages: 16-17

RS pages: 11 charge and current puzzle

What would this voltmeter read?12 voltsYou don’t calculate the Voltage of a battery, you read it off the label.

12 V

5

V

What would this voltmeter read? zero voltsThere is not reason for the voltage to change from one part of a wire to the other.

12 V

5

V

∆V=IR

𝑛𝑜 𝑟𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒 =no voltage drop

∆V=?0

What would this voltmeter read?

12 V

5

V

zero voltsThere is not reason for the voltage to change from one part of a wire to the other.

∆V=IR ∆V=?0

What would this voltmeter read? 0 voltsThis is an open circuit with no current flowing.With out flow there is no resistance = no drop in voltage.

12 V

5

V

∆V=0?∆V=IR


12 V

5

V

12 voltsThis is an open circuit with no current flowing.With no flow there is no resistance = no drop in voltage on either side of the wire.

What would this voltmeter read? 12 voltsThis is an open circuit with no current flowing.With no flow there is no resistance = no drop in voltage on either side of the wire.

12 V

5

V


12 voltssince current will not flow through a volt meter.(same a previous)

12 V

5

V

0 ampssince no current flows through a voltmeter

12 V

6

V

A0 voltssince no current flows through a voltmeter

What would this amp meter and Volt meter read?


12 V

6

VA 12 volts

since no current flows through a voltmeter



12 V

6

VA


12 voltssince no current flows through a voltmeter

What would this ammeter meter read?

12 V

6

V

2 ampsI = V/RI = 12/6I = 2 ampsThe amount of current going through the meters is the same as the current in every part of the circuit.


2 ampsI = V/RI = 12/6I = 2 ampsThe amount of current going through the meters is the same as the current in every part of the circuit.

12 V

6

V


1000+ ampsYou just shorted the circuit.I = V/RI = 12/0As R approaches zero Current approaches infinity.

I = ∞ amps

12 V

6

A


12 V

6

A

1000+ ampsYou just shorted the circuit.I = V/RI = 12/0As R approaches zero Current approaches infinity.

I = ∞ amps

A fuse is placed in series so that the current of the circuit passes through it.

If too much current passes through it, the fuse heats up and the conductor (wire) melts. This opens the circuit preventing any more current flow.

A circuit breaker is placed in series so that the current of the circuit passes through it.

If two much current passes through it, the circuit breaker temporarily opens the circuit preventing any more current flow.

Wires that are carrying too much current heat up and often are the cause of fires.

video: Ohms Law by Eugene

Calculating Resistance seriessimply add up all resistances to find total resistance. Rt = R1 + R2 + R3….

5 3 2

Rt = 10

A wire carrying current (moving electrons)

orA pipe carrying water.

(moving water molecules)

Resistance slows down the flow by taking energy from the moving particles.

What is the resistance for each section of wire?

5 515

30

2

Resistance is related to the amount of energy lost as current passes by.

The smaller the wire the greater the resistance and the harder it is to push current through.

5 515

30

2

100 v100 psi

95 v95 psi

5 515

30

2

95 v95 psi

80 v

5 515

30

2

80 v80 psi

78 v

5 515

30

2

78 v 48 v

5 515

30

2

48 v 43 v

Going through 5,15,2,30,5 resistors is the same as going through one resistor of 57

5 515

30

2

57

Important to remember:

Bigger wire (pipe) results in small (less) resistance.

575 5

Calculating Resistance parallel

1

𝑅𝑓

=1

𝑅1

+1

𝑅2

+1

𝑅3

5 3 2

Calculating Resistance parallelAdd the reciprocal of each resistance then invert the sum to get the total resistance.

Rt = 30/31= .97

5 3 2

5 + 3 + 2 1 + 1 + 1

30 + 30 + 30 30 6 + 10 + 15 31

5

3

2

5

3

2

This hole has 5 resistance.



If were to replace the 5, 3, and 2 holes with one resistive hole, How big would it need to be? and what would it’s resistance be?

1

5 3 2 1

1

5

3

2

5 Gallons per minute

5 Gallons per minute

video: Circuit Analysis Crash Course #30

Which wires carry electrons with same emfpushing on them.

Colors = voltage

Colors = voltage

4v

5v 3v

4v

4v

The current through all elements in series is the same.The Voltage across all elements in parallel is the same.Ohms Law V = IR ( I = V/R R = V/I )Equivalent Resistance of resistors in series = sum of resistors

Equivalent Resistance in parallel = inverse of the sum of resistors inverses

Voltage drops (energy is lost) when current goes through a resistance.Energy lost (transferred) is called power P = VI Watts = Volts * Amps

1

𝑅𝑓

=1

𝑅1

+1

𝑅2

+1

𝑅3

Rt = R1 + R2 + R3….

1

𝑅1

+1

𝑅2

+1

𝑅3

1𝑅𝑓 =

Key Concepts Electrical Currents

RS practice pages: 18, 22, 23

RS charge and current quiz

circuits and electrical diagrams · 2019. 8. 12. · the voltage across all elements in parallel is...

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