Physical Science Final

Circuit Diagram

-Graphical Representation of an electrical circuit, illustrates the path of desired electrical circuit

Does a battery create electric charge? Why/why not?

A battery only stores electric charge.

What is an Ohmmeter?

An instrument for measuring electrical resistance. (The multimeter is capable of measuring resistances directly, by internally measuring the current and voltage at the same time. When in this mode, the multimeter can also be called an Ohmmeter.

Loop Rule

Around any closed loop in a circuit, the voltage drops and gains must add up to zero -Consistent with the conservation of energy

What is the loop rule?

Around any closed loop in a circuit, the voltage drops and increases must add up to zero.

Where in the circuit is there a voltage increase?

At the battery

Junction Rule

Current flowing into any junction is equal to the current flowing out of that junction -Consistent with the conservation of charge

Parallel Circuits

are brighter

Voltage increases

from - to + aka over a battery in a circuit

Electrons flow....

from low to high -By the time electrons reach the + end of the battery, they've lost all their potential energy -Reversing the direction of a battery reverses electron flow.

Current and Voltage

have a linear relationship; as one increases, so does the other. Linear indicates faster flow of electrons; steeper the slope, easier electrons are pumped through.

Proton

high PE to low PE

Conductors will have ___ resistance

low

Electron

low PE to high PE

Magnetizing a nail

means aligning its elementary magnets -Permanent magnets still have elementary magnets, they're just harder to knock out of alignment (heating it will demagnetize it)

What is a normal voltage for a battery? For a fruit battery?

-1.5 V is the highest you can make with 2 suitable metals -An acid + 2 pieces of metal make a battery

Draw a sketch of a light bulb and explain how it works.

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Only special circuits can be classified as purely series or purely parallel. Draw a circuit diagram that has one battery and five bulbs with some in series and some in parallel.

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2 Primary Requirements of an Electric Circuit

1. Voltage Source 2. Circuit [low to high voltage (closed loop)]

Requirements for flow of charge

1. Voltage source 2. Circuit

A 1.5 volt battery is used in a simple circuit with a bulb. What is the voltage drop across the bulb?

1.5

A charge of 3200 C flows through a light bulb in 1 hour. How many electrons have passed through the bulb within this 1 hour? What current does this flow of electrons correspond to?

11,520,000 A The Electric Current

A 1.3 volt battery is combined in series with a 1.2 volt battery. What is the voltage across this combination?

2.5V

The potential difference between a storm cloud and the ground is 100 million volts. If a charge of 2 C flashes in a bolt from cloud to Earth, what is the change of potential energy of the charge?

200 mil J

Three wires meet at a junction. One carries 120 mA in, the second carries 350 mA in. How much must the third wire carry out?

470mA

Three wires meet at a junction. One carries 240 mA in, the second carries 750 mA out. How much must the third wire carry? Is the current in the third wire flowing out of or into the junction?

510mA

A 6 volt battery is used in a parallel circuit with two bulbs. What is the voltage drop across the first bulb? What is the voltage drop across the second bulb?

6V across first, 6V across second

A 6 volt battery is used in a series circuit with two bulbs. If the voltage drop across the first bulb is 3.5 V, what is the voltage drop across the second bulb?

6V-3.5V= 2.5V 2.5V

Why would aluminum foil dissolve into food in a stainless steel container?

A battery is made from acid and two metals so the acid from the food, with the foil and the steel, makes a battery that conducts current in the form a chemical reaction (which dissolves the foil).

Does a battery provide the same current to any circuit? What does it actually provide?

A battery will supply as much current as the circuit will allow.

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A brighter bulb will have a larger voltage drop

Parallel Circuit

A circuit composed of two (or more) components connected in parallel. -In a parallel circuit, the voltage across each of the components is the same, and the total current is the sum of the currents through each component -In parallel circuits, each light has its own circuit, so all but one light could be burned out, and the last one will still function. -Parallel circuits (generally) are much brighter -Current increases with each additional pathway

What is a resistor?

A device having resistance to the passage of an electric current.

What does a multimeter do?

A multimeter measures different quantities of interest in a circuit. We used the multimeter to measure electric potential difference, or Voltage. A good initial setting when working with batteries is the 2 volt range. -Only differences in electric potential can be measured, thus you must place the leads of the multimeter at different points in the circuit to obtain measurement.

We know that the voltage drops across a bulb. We also know that the voltage does not change on a conductor. Where inside of the bulb does the voltage actually drop?

Across the filament

What happens to the current in other bulbs if one bulb in a series circuit burns out?

All bulbs will go out and the the current will be zero.

Series Circuit

An electric circuit connected so that charges move in "series" first going to one resistor then the next -In a series circuit, the current through each of the components is the same, and the voltage across the circuit is the sum of the voltages across each component. -In a series circuit, every device must function for the circuit to be complete. One bulb burning out in a series circuit breaks the circuit

Ohm's Law

Current through a resistor is directly proportional to voltage across that resistor and inversely proportional to resistance of that resistor

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Currents only change at junctions

Imagine you place an electron and a proton in an area between high electric potential to one side and low electric potential to the other side. Toward which direction will each particle move? Why?

Electron moves from low to high Proton from high to low

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Electrons lose energy through heat (resistor) and light (light bulb)

Resistor Color Codes

Hold resistors so error band is on the right -Error bands indicate accuracy of resistor -Resistors read from left to right R= (10 x color1 + color2) x 10^color 3

What happens to the current in other bulbs if one bulb in a parallel circuit burns out?

If one lamp in a parallel circuit burns out, the other lamps are unaffected because current still flows through them. Total current in the system is reduced by the loss of the burned out lamp

Where in a circuit does the voltage stay the same?

In a series circuit.

Direction of Electron Flow in Parallel Circuits

Negative end of battery to positive end - > +

What happens to the brightness of each bulb in a parallel circuit if more bulbs are added (in parallel) to the circuit?

Nothing happens to the brightness of the light bulbs in the parallel circuit if the power supply is capable of supplying the additional current. Otherwise, the original bulbs will dim according to the additional current demand.

What three quantities are related by Ohm's Law? Solve Ohm's law algebraically for each of these quantities?

Ohm's Law is V = IR V - the voltage I - the current R - the resistance

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Only differences in electric potential can be measured (voltage)

Which type of circuit has brighter bulbs?

Parallel

Which type of circuit requires the most current flow through the battery?

Parallel

What is the resistance of a perfect conductor? A perfect insulator?

Perfect Conductor: low resistance Perfect Insulator: high resistance

Direction of Current Flow in Parallel Circuits

Positive end of battery to negative end + > -

What is resistance?

Prevention or restriction of the flow of electric current. A substance resists electrical current because of a collision between electrons and atoms, which slows the electrons down and converts some of their energy to heat energy. In some cases, the energy is also converted into light Resistance is measured in Ohms.

A resistor has the colored bands ORANGE - GREEN - YELLOW. What is its resistance?

R= (10 * color 1 + color 2) * 10^color 3

Resistors in parallel

Resistance will be less because there are more pathways -Equivalent of resistance in parallel is less than each individual resistor's value

If you place the red lead of the multimeter on the (+) end of a battery, but leave the black lead disconnected, the multimeter will read zero even though the (+) end of the battery is held at high electric potential. Why?

The black lead of the multimeter always goes to the reference point with respect to which you want to measure the potential. The multimeter then displays the potential at the red wire minus the potential at the black wire. To measure the voltage between points A & B, you place black wire at A and red wire at B. (on either side of the thing you're testing)

If two bulbs are in series, what can you say about the current flow through them?

The current flowing through them is the same

What is Ohm's Law?

The current through a resistor is directly proportional to the voltage across that resistor, and inversely proportional to the resistance of that resistor.

Electric Current

The rate of charge flow, measured in Coulombs per second (C/s), also known as Amperes (A). -The current is opposite of the flow of electrons

The Junction Rule

The sum of the all currents flowing in to a junction is equal to the sum all currents flowing out of the junction, based on the Conservation of Charge -Applies to a current at a junction of 3 or more wires Formula: Ia= Ib + Ic

What is electric potential?

The total capacity for elections Also called voltage, which is the potential energy per charge

What property of the battery has the largest effect on its voltage?

The type of chemicals used

What happens to the brightness of each bulb in a series circuit if more bulbs are added (in series) to the circuit?

They get dimmer, since it is a series circuit, all bulbs are exposed to the same current, and every bulb adds resistence (measured in ohms) reducing the amount of energy each bulb has (measured in amperes) since the bulbs have less energy to use, they give off less energy, resulting in a weaker light.

What is the voltage (potential!) at the location of a 0.0001 C charge that has an electric potential energy of 0.5 J (both measured relative to the same reference point)?

V= 5000 J/C

Where in a circuit is there a voltage drop?

Whenever current passes through a resistance of some kind, a voltage drop occurs across that resistance. The amount of the drop is given by Ohm's Law: V=IR Where: V = The value of the voltage drop I = The current through the circuit in amperes R = The total resistance of the circuit

Ohmeters test faulty circuits

because a faulty wire will have a lot of resistance

Ammeters

measure electric current in a wire

Multimeters

measure resistance directly by simultaneously measuring internal voltage and current

Resistors

restrict flow of electrons or current

Voltage difference

the positive end of a battery is held at high electric potential and the negative at low potential such that this difference acts a pump for electrons.

Electric Current

the rate of charge flow