Electric Circuits and Power
Be able to label the symbols used in a circuit diagram.
+/- = energy source; open door =switch; squiggle line = resistor; line = wire
What is the voltage in most household circuits?
120 volts
What is the difference between a wet cell and a dry cell?
A wet cell is an electrochemical cell in which the the electrolyte is a liquid,like sulfuric acid; a dry cell is an electrochemical cell in which the electrolyte is a paste. Flashlights use dry cells; car batteries use wet cells.
What was the first battery?
Alessandro Volta, an Italian scientist, invented it; it had a layer of zinc (electrode1), paper soaked in salt water (electrolyte), and silver (electrode2), all with a brass hook on each end. The more layers, the more current that was produced, because the chemical reaction occurred between the different metals.
What units are used to measure current (I)?
Ampere (A) (the amount of charge flowing past a given point each second = number of amperes.
What is the difference between magnetism and electricity?
Both say that charges that are opposite attract each other and charges that are the same repel each other, but with magnetism, poles cannot exist alone. Where there is a north pole, there must be a south pole. With electricity, one charge may exist without the other.
How do the components of an electrochemical cell produce voltage?
Electrons have opposite charge; there is voltage between them. Chemical reactions occur between the electrodes and electrolytes in an electrochemical cell. One becomes positive, and one becomes negative.
What is the equation to find out how much energy an appliance uses?
Energy = power (1000W) x time(hours)= KW per hour = KWh
Who performed experiments in the 1800s that demonstrated the relationship between current, voltage, and resistance?
George Ohm
What happened when Volta connected the parts of his cells in a circuit?
He created more current; the more layers of zinc, paper, silver that he added, the more current.
What would happen if the circuits in your school building were series circuits? Explain.
If all of the circuits in your school were series circuits, then when one light was turned off, every light would go off. This is because there would only be one path for the current to take. If the power blew in one place, it would shut down all electricity.
What does a switch do for a circuit?
It opens and closes the circuit.
Can height cause current in an electric circuit?
No. Current is caused by the difference in electrical potential energy between two places in a circuit.
What is Ohm's Law?
REsistance =voltage/current
What happens when more branches are added to a parallel circuit?
The current has more paths to follow, and the resistance decreases.
What are three basic features of a circuit?
They have DEVICES run by electrical energy; they have a SOURCE of electrical energy; and electrical circuits are connected by conducting wires.
What do batteries do?
They transform chemical energy into electrical energy.
Is the following a characteristic of a series circuit, parallel circuit, or both? current=voltage / resistance
This is an example of both a series and a parallel circuit.
Explain static discharge
This is the LOSS of static electricity when a electric charges transfer from one object to another--like when you touch a dooknob and get a shock--the electrons are transfered between your hand to the door and heat the air around the path they travel, producing a spark. Lightning is an example of static discharge.
The law of conservation of charge
This law states that charges are neither created nor destroyed when electrons are transferred from one place to another. If one object gives up electrons, then another one gains those electrons.
Is this true or false: For circuits with the same resistance, the greater the voltage, the greater the current?
True, because Ohm's law says R = V/A, so if R stays the same and V goes up, then A would have to go up as much as V.
Formula for resistance
Voltage/current = resistance
Which transforms energy at a faster rate--a 100 W bulb or a 60 W bulb?
a 100 @ bulb (bright light)
parallel circuit
a circuit where the different parts are on separate branches; there are several paths that the current can take
What is a battery?
a combination of two or more electrochemical cells in a series. Cells usually refer to a simple electrochemical cell; batteries usually refer to multiple cells in a series. In a battery, the positive terminal of one cell is connected to the negative terminal fo the next. The total voltage is found by adding the voltage of the cells.
What is a short circuit?
a connectioin that allows current to take the path of least resistance
What is an electrochemical cell?
a device that converts chemical energy into electrical energy; it has two different metals called electrodes, which are soaked with an electrolyte (a substance that conducts electric current)
Voltage source
a device that creates voltage in an electric circuit (batteries/generators)
ammeter
a device used to measure current/series circuit
voltmeter
a device used to measure voltage
conductors
a material through which charges can flow easily (metals/inner wire)
insulator
a material through which charges cannot flow easily (rubber, plastic, glass, sand)
If total resistance increases as more branches are added, what kind of circuit is being used?
a parallel circuit
What kind of circuit provides a path for current to wall sockets and appliances in a home?
a parallel circuit
If the current in each part of the circuit is the same, what kind of circuit is being used?
a parallel?
If a break in any part of a circuit causes the current to stop, what kind of circuit must it be?
a series circuit
If total resistance increases as more light bulbs are added, what kind of circuit is being used?
a series circuit
Series Circuit
a type of circuit with only one path for the current to take/all parts of an electric circuit are connected one after another.
Who is Luigi Galvani?
an Italian physician used a brass hook to hold a leg muscle of a frog in place and found out that the muscle twitched if he attached the hook to an iron railing. = hypothesized that there was electricity in living tissue
What are two examples of SOURCES of electrical energy?
batteries and generators--devices that create a potential difference in an electrical current.
Why does a resistor represent a DEVICE run by electrical energy?
because it transforms electrical energy to light
Why do the bulbs become dimmer as more of them are added to a series circuit?
because the resistance increases and the current decreases in such a circuit, resulting in less energy transfered to light.
What are three ways that an object can be charged?
induction, conduction, friction
three ways an object can become charged
induction, friction, conduction
electric current
is measured in Ampere (A)/the continuous flow of electric charges through a material
What are four factors that determine the resistance of a wire or object?
material from which the wire is made; length; diameter; temperature. Long wires have more resistance than short wires; smaller diameter results in more resistance higher temperature = less resistance.
Induction
movement of electrons to one part of an object that is caused by the electric field of the second object
What units are used to measure resistance (R)?
ohms (funny sign like omega)
electric circuit
the complete, unbroken path through which electric charges flow
Voltage
the difference in electrical potential energy between two places in a circuit/causes a current in an electric circuit/volt(V)/Voltage (volts) =current (amps) X resistance (ohms)
Electric field
the region around a charged object where the object's electric force affects other charged objects; the other charged objects are either pushed or pulled.
friction
the transfer of electrons from uncharged object by rubbing
How is lightning formed
through static discharge/It is like a big spark/water droplets become electrified; to restore the neutral condition in the clouds, electrons move from places with negative charge to those of positive charge and produce a spark--lightning. Negaive charges at the bottom of the clouds can cause the Earth's surface to become positively charged by induction. Then,electrons can jump from the cloud and Earth's surface, producing lightning bolts because of conduction, which causes another charge.
conduction
transfer of electrons from a charged object to another object by direct contact
Name the parts of an electrochemical cell.
two terminals--positive and negative (electrode part above the surface of the electrolyte); electrodes, electrolyte
What units are used to measure voltage (V)?
volts (V)
charges that flow continuously from one place to another
what you need to produce an electric current
Static discharge
when a negatively charged object and a positively charged object are brought together/the electron transfer that occurs until both objects have the same charge
static electricity
when charges build up on an object but don't flow continuously; static electricity involves the transfer of electrons from one object to another by conduction, induction, or friction.
POwer
when energy is transformed from one form to another =voltage X current
