This document presents information about electrical circuits and their components. It discusses how batteries and generators convert different types of energy into electrical energy. It then describes common circuit components like light bulbs, motors, and speakers that convert electrical energy into other forms. The document goes on to explain key electrical concepts such as electric current, voltage, resistance, and Ohm's law. It provides examples of how circuits work and how measurements can be taken.
1. presents
a production
Everything Electric
Episode 2
Vaguely Voltage
2. Simple circuit
Source: chemical to electrical
Connection: conduct electricity
with almost no energy change
Component: electrical to
light and heat
3. Sources of electrical energy
They convert different types of energy to electrical energy
Batteries:
Chemical
to
Electrical
Image credit: Ian Britton @ FreeFoto.com
Image: US Department of Energy
Eel: Atomic power station:
Chemical Nuclear
to to
Electrical Electrical
Image: Aaron Gustafson @ ïŹickr.com
4. Components
They convert electrical energy to different types of energy
produces heat energy
produces heat energy
produce light and
heat energy
produces sound, kinetic
and heat energy
produces kinetic
and heat energy
5. What is Electric Current?
Electric current is the ïŹow of electric charge
Q
Ixt
Charge, Q is measured in coulombs (C)
Current, I is measured in amperes (A)
Time, t is measured in seconds (s)
One ampere = One coulomb per second
Current ïŹowing = Charge passing Ă· time taken
6. Conventional current
electrons
electrons
electrons
electrons
Electrons travel around the circuit from - to + terminals of
the battery, but the arrows on the wires for the
conventional current are drawn the other way.
8. Parallel circuits 2
Think of them as Ladder circuits
Try this out: http://
phet.colorado.edu/en/
simulation/circuit-
construction-kit-ac
When a new component is
connected in parallel, the
current in the existing
components does not change,
although the current from the
battery will increase
9. Series circuits
Think of them as Chain circuits
This circuit contains 3 cells and 3 bulbs in series
What happens if you change the number of bulbs?
What happens if you change the number of cells?
10. Q: What happens if
you reduce the
number of bulbs
but keep the cells
the same?
A: The bulb gets brighter.
This means the electric
current is higher.
11. Q: What happens if
you reduce the
number of cells
but keep the bulbs
the same?
A: The bulbs get dimmer.
This means the electric
current is lower.
12. What is Voltage?
also known as potential difference
voltage is the energy transferred per unit charge passed
1 volt = 1 joule per coulomb
A battery of voltage 6.0 volts gives 6.0 joules
of energy to each coulomb which passes
Energy, E in joules
PD,V in volts E
Charge, Q in coulombs Q xV
13. Ammeters and voltmeters
To measure V and
I in the bulb...
A current ïŹows through
the component
Ammeter connected in
series - you must break
the circuit to connect it
A voltage is applied
across the component
Voltmeter connected in
parallel - just touches
the wires at either side
14. Measuring V and I
Apply different voltages across a
component (this one is a bulb) by adding
more cells (or using a variable power
supply).
Circuits created at echalk.co.uk
Plot a graph of V
against I
15. Current in bulbs and resistors
Results for actual investigation using variable power supply
16. Current in diodes
Image: Erik Streb @ wikipedia
When the voltage is positive, the
diode conducts electricity, but
when the voltage is reversed, the
diode blocks the current.
Image: Theresa Knott @ wikibooks
17. Light emitting diodes
When the voltage is positive, the
diode conducts electricity, but
when the voltage is reversed, the
diode blocks the current
When current ïŹows in
the LED, it emits light; if it
is connected in reverse,
no current will ïŹow.
Image: Pete Scamper
19. Ohmâs Law
The current through a metallic conductor is directly
proportional to the voltage across its ends if the
temperature and other conditions are constant.
Image: bbc gcse bitesize
Explore Ohmâs Law with PHET simulation
20. Light-Dependent Resistors
Also known as LDRs or photoresistors
When bright light shines on it, the
resistance is low and the current is high.
Image: ladyada.net
Image:
Benthewikiman
@ wikipedia
21. Thermistors
Also known as Negative Temperature CoefïŹcient (NTC) Resistors
When the temperature is high, the
resistance is low and the current is high.
Image: Julong Technology Ltd
Image: Arroyo Instruments
22. How a circuit works
When the electrons return to Each coulomb takes 6.00 J of
the battery, all electrical energy electrical energy from the battery.
has been converted.
0.75 J Almost no
electric energy change
All 6.00 J has to light/ in the wire;
been converted heat still 6.00 J/C
from electric
energy.
3.00 J electric to light/ heat
Each coulomb loses
2.25 J electrical
energy to light and
heat in this bulb
23. a production
MUCH MORE AT
http://nothingnerdy.wikispaces.com
http://nothingnerdy.wikispaces.com/ENERGY+AND
+POTENTIAL+DIFFERENCE+IN+CIRCUITS
Hinweis der Redaktion
Welcome to nothingnerdy’s presentation on Everything Electric. Part 2: Vaguely Voltage\n
An electric circuit has three elements. The source (such as an electric cell) provides electrical energy to the moving charges by converting it from other energy types. The components, such as the bulb here, convert electrical energy to other forms, such as heat and light. Between the different components and the source there will be conducting connections, such as wires which make a complete loop.\n
Here are three examples of sources converting other forms of energy to electrical.\n
There are many different components which convert electrical energy to other forms when connected in an electric circuit.\n
Electric current is one of the quantities we often measure in electric circuits. It is defined as the rate of flow of electric charge and is measure in amperes. Charge is measured in coulombs. When one coulomb passes a point in a circuit in one second, this is one ampere. When the time is measured in seconds, we can use the formula Charge=Current * time or Q = It\n
We know that current in a wire is the flow of electrons and that these are negative charges. They flow from the negative terminal on a battery round the circuit to the positive terminal losing their electrical energy on the way. Long before the electron was discovered, scientists guessed that current flows from + to -. They were wrong but it was too late. When we draw arrows to show the direction of current, it is from + to -, the opposite direction to the flow of electrons. Sorry, that’s just the way it is.\n
Here are many of the names and symbols of the most common electrical components.\n
Parallel circuits are connected like a ladder which means that you can remove or add new components, like rungs in a ladder, without affecting the other components. to this simple circuit, we add bulbs in parallel and note that all of the bulbs have the same current in them. It is the battery which provides more and more current.\n
The components in a series circuit are joined like a chain. If one component fails, the whole circuit stops working. Let’s see what happens when the number of bulbs is changed...\n
When there are fewer bulbs but the same number of cells, the remaining bulbs are brighter because there is now more current.\n\nLet’s now see what happens if the number of cells is changed.\n
When we reduce the number of cells but keep the bulbs the same, the bulbs are now dimmer. This is because the current is lower.\n
As well as current in a circuit, we also measure voltage. Voltage (aka PD) is the amount of energy transferred for every unit of charge which passes. If one coulomb of charge receives 6 joules of energy from a battery, then the voltage of the battery is 6 volts. You can measure the voltage across a source or across a component.\n
Current in amps is measured by an ammeter; voltage in volts is measured by a voltmeter. They are connected in different ways. The current passes through the ammeter so it is connected in series. The voltmeter measure the voltage across the component, so it is connected in parallel.\n
This is an important circuit in which the voltmeter and ammeter are connected to measure the relationship between V and I for a component such as a bulb. The voltage is changed by adding new cells, and each time the new voltage and current are measured.\n
Here are the results of two real experiments measuring V and I for a bulb and a resistor. We can see that the result for the resistor is a straight line, but for the bulb it curves upwards.\n
If you plot the V-I graph for a diode, the current passes in one direction, when the voltage across the diode is positive, but when the voltage is reversed, the diode blocks the current. The symbol is shown above and the triangle shows which way the current flows.\n
A LED, like a diode, only conducts in one direction. It emits light and can be used to show the presence of a current. But if it is connected in reverse, no current flows. The symbol shows a diode with rays of light coming from it.\n
Resistance measures how much a conductor opposes current. The formula is V=IR as can be seen in the triangle on the slide. For a certain voltage, the current and resistance are inversely proportional. This means that if the resistance is high, the current is low and vice versa. For a component, resistance is calculated by dividing voltage by current. The unit of resistance is the ohm which is equal to 1 volt divided by 1 amp.\n
For certain conductors, when the temperature is constant, the voltage across it is proportional to the current (straight line through the origin). That means the graph of V against I is a straight line. This also means that the resistance is constant. These components, such as resistors, obey Ohm’s Law (they are ohmic). Other components have a varying resistance (such as bulbs and diodes) and are called non-ohmic.\n
As the name suggests, LDRs have a resistance which changes with the brightness of the light falling on them. As you can see in the graph, the resistance is low when the brightness is high. This means a high current flows - it could ring a buzzer for instance. You can also see the symbol here with rays of light falling on a resistor symbol.\n
The resistance of a thermistor changes with the temperature. When it is hot, the resistance falls which means that the current is high - it could operate a fan, for example. The symbol is a resistor with a bent line across it as shown on the slide.\n
We can put together all of the ideas about circuits and energy. The battery gives 6J of energy to each coulomb that passes through it. In the wires, almost no energy os transferred. At the branch, three times more energy is converted in the low resistance bulb. After the parallel bulbs, there is still 3J remaining on each coulomb which all gets converted in the last bulb so that when the charge returns to the battery, it has transferred all 6J. The conventional current goes in the opposite direction\n
