Physical Science Test 3 Gerner

If 2 oppositely charged particles are brought closer together so that the distance between them halves, the force will be multiplied by 1/4

False

(It will multiply by 4 because they're coming closer together instead of farther apart)

In order for electric charge to flow, there must be a difference in electric potential.

True

Flow is called current and is measured in amperes

True

Voltage source supplies continuous difference in electric potential by separating opposite charges

True

A voltage source contains all electrons that flow in a circuit

False

If an object becomes polarized it transfers electrons to a different object

False

(Cannot transfer electrons)

When connected to the same voltage, a lamp with a thicker filament will draw less current than a lamp with a thinner filament

False

(One with thicker filament has lower resistance and higher current)

Electric fields of like charges are attracted to one another

False

Like repels, opposites attract

The device with the largest resistance will have the largest voltage drop in a series circuit

True

In a parallel circuit, the current through a given branch is directly proportional to its resistance

False

(it is indirectly proportional)

As the number of branches increases in a parallel circuit, the total resistance decreases and the total current increases

True

In a parallel circuit, each device connects to the same two points, so the voltage across each device is the same

True

Which part of an atom is positively charged? Negatively charged?

Nucleus and protons are positive; electrons are negative

How does the charge of one electron compare with the charge of another electron?

Identical charges

How does the number of protons in the nucleus compare with the number of electrons that orbit the nucleus?

Protons and electrons normally equal

What kind of charge does an object acquire when electrons are stripped from it?

When electrons are stripped, it is left with a positive charge

What is meant by saying charge is conserved?

Charge cannot be created or destroyed, merely transferred

How is Coulomb's law similar to Newton's law of gravitation? How is it different?

Both laws are inverse-square laws. How they differ is mainly that gravitation is only attractive, whereas electrical forces can repel.

How does the magnitude of electrical force between a pair of charged particles change when the particles are moved twice as far apart? Three times as far apart?

By the inverse-square law, particles twice as far apart have 1/4 the force; three times as far apart, 1/9 the force.

How does an electrically polarized object differ from an electrically charged item?

Charge in a polarized object is simply re-arranged, with a net force normally zero. A charged object has a non-zero net charge.

Give two examples of force fields

Electric and gravitational

How is the direction of an electric field defined?

The direction of an electric field is the direction of force on a positive charge.

Distinguish between electric potential energy and electric potential in terms of units of measurement.

Electric potential energy is measured in joules; electric potential is measured in volts.

A balloon may easily be charged to several thousand volts. Does that mean it has several thousand joules of energy?

No. Several thousand volts is different than the ratio several thousand volts per coulomb. Voltage is measured in volts; voltage/coulomb is energy and measured in joules.

What condition is necessary for a sustained flow of electric charge through a conducting medium?

A sustained flow needs a sustained difference in potential across a conducting medium, such as a battery or generator.

How much energy is given to each coulomb of charge passing through a 6V battery?

Six joules of energy are given to each coulomb of charge passing through a 6-V battery.

Distinguish between ac and dc

Direct current, moving in one direction, is dc. Alternating current, moving to and fro, is ac.

Does a battery produce dc or ac? Does the generator at a power station produce ac or dc?

A battery produces dc. A generator normally produces ac.

Which has greater resistance: A thick wire or a thin wire of the same length?

A thin wire has a greater resistance (just as a thin pipe greater resists water flow).

What is the unit of electrical resistance?

The unit of electrical resistance is the ohm, symbol .

What is the effect on current through a circuit of steady resistance when the voltage is doubled? When both voltage and resistance are doubled?

When only voltage is doubled, current is also doubled. If both voltage and resistance are doubled, the current doesn't change.

Which has greater electrical resistance: wet skin or dry skin?

Dry skin has considerably more electrical resistance than wet skin.

What is the function of the third prong on the plug of an electrical appliance?

The third prong is connected to the "ground," providing a route for unwanted charge. It prevents charge buildup on the appliance.

In a circuit consisting of two lamps connected in series, if the current in one lamp is 1 A, what is the current in the other lamp?

The same, for the same current passes through each lamp that is connected in series.

How does the total current through the branches of a parallel circuit compare with the current through the voltage source?

The current through the voltage source is the sum of the currents in the branches.

Electric power is the rate at which electric energy is converted into another form

True

The unit of power is the Watt

True

Multiplying electric power by time gives the amount of electric energy converted to another form

True

As more lines are opened at a fast-food restaurant, the resistance to the motion of people trying to get served is reduced. How is this similar to what happens when more branches are added to a parallel circuit?

The more branches in both cases, the less the overall resistance. 30. The relationship is given by the formula, power current voltage.

Why is charge usually transferred by electrons rather than by protons?

Electrons are loosely bound on the outside of atoms, whereas protons are very tightly bound within the atomic nuclei.

A car's headlight dissipates 40 W on low beam and 50 W on high beam. Is there more or less resistance in the high-beam filament?

There is less resistance in the higher wattage lamp. Since power current voltage, more power for the same voltage means more current. And by Ohm's law, more current for the same voltage means less resistance.

Your tutor tells you that an ampere and a volt really measure the same thing, and the different terms only make a simple concept seem confusing. Why should you find another tutor?

Your tutor is wrong. An ampere measures current, and a volt measures electric potential (electric pressure). They are entirely different concepts; voltage produces amperes in a conductor.

Electric power is the rate at which electric energy is converted into another form

True