Physics B Review

Calculate the current in a 140-W electric blanket connected to a 120-V outlet.

(P=I x V) I = P / V = (140 W) / (120 V) = 1.17A

If three lamps are connected in series to a 6-volt battery, how may volts are impressed across each lamp?

2 Volts across each lamp.

Checked and approved by Mr. Nedland.

5/11/2015

If three lamps are connected in parallel to a 6- volt battery, how many volts are impressed across each lamp?

6 Volts across each lamp.

Is an electron in hydrogen atom the same as an electron in uranium atom?

All electrons are identical.

What kind of field surrounds a stationary electric charge?

An electric field.

How is a gravitational field and an electric field similar?

Both fields exert forces.

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

Both laws are inversed square laws.

Does voltage flow through or across a circuit?

Charge flows through a circuit and voltage across a circuit.

What is a major difference between electric charges and magnetic poles?

Charges can be isolated, whereas poles cannot.

What are the three main methods of charging objects?

Contact, friction, and induction.

What is a generator, and how does it differ from a motor?

Converts mechanical energy to electrical energy. whereas a motor converts electrical energy to mechanical energy.

Distinguish between dc and ac. Which is produced by a battery and which is usually produced by a generator?

DC is produced by battery and flows in one direction, whereas AC is produced by generator and alternates direction.

Does diffraction aid or hinder radio reception?

Diffraction aids radio reception.

Does diffraction aid or hinder the viewing of images in a microscope?

Diffraction hinders the viewing of images in a microscope.

What was Thomas Young's discovery?

Discovered that when monochromatic light was directed through two closely spaced pinholes, fringes of brightness and darkness were produced on a screen behind, creates by light waves.

What kind of field surrounds a moving electric charge?

Electric and magnetic fields.

The proportionality constant k in Coulomb's law is the ordinary units, whereas the proportionality constant in G in Newton's low of gravitation is tiny. What does this mean in terms of the relative strengths of these two forces?

Electrical force is usually much greater.

Every spinning electron is a tiny magnet. Since all atoms have spinning electrons, why are not all atoms tiny magnets?

Electrons spin in opposite directions, so their fields cancel out.

Suppose the speakers at an open-air rock concert are pointed forward. You move about and notice that the sounds of female vocalists can be heard in the front of the stage but very little off the sides. By comparison you notice the bass sounds can be heard quite well both in front and off to the sides. What is your explanation?

Female vocalist's shorter wavelengths diffract less than longer wavelengths of the bass.

Is electric resistance greater in short fat wires or long and thin wires?

Greater resistance in a long thin wire than a short fat wire.

Calculate the current of a lightning bolt that delivers a charge of 35 coulombs to the ground in a time of 1/1000 of a second.

I = (35 C) / (10^-3 s) = 35,000 Amperes

Why are household appliances almost never connected in series?

If one device failed, current would not continue to the rest of the circuit. Also, with more appliances, the less efficient they'd run.

Which method of charging involves no touching between the two objects?

Induction.

Why is an electrical field considered a vector quantity?

It has magnitude and direction.

What is the function of the third prong in a household electric plug?

It is a ground for electrical safety.

Why does the weaker force of gravity dominate over electrical forces for astronomical objects?

It is not affected by repelling forces and acts on large masses.

What will happen to the electrical potential energy of a charged particle in an electric field when the particle is released and free to move?

It transforms kinetic energy.

How does light from a laser differ from light coming from a ordinary lamp?

Lamp light is incoherent where a laser is coherent.

Can a laser put out more energy than is put in?

Lasers can not put out more energy than is put in. It must follow the Law of conservation of energy.

What is light?

Light is simply electromagnetic waves in range of frequencies.

What are electric field lines?

Lines depicting an electric field.

How does wetness affect the resistance of your body?

Lowers resistance of your body.

A motor is characterized by three main ingredients: magnetic field, moving charges, and magnetic force. What are the three main ingredients that characterize a generator?

Magnetic field, moving charges, and magnetic force.

With respect to an electric and a magnetic field, how does the direction of a magnetic force on a charged particle differ from the direction of the electric force?

Magnetic force is perpendicular to the field and electric force is parallel to the field.

What must a charged particle be doing in order to experience a magnetic force?

Moving.

When a conductor is charged, the charge moves to the outer surface of the conductor, why is this so?

Mutual repulsion.

How are Coulomb's and Newton's law of gravitation different?

Newton's depends on mass and Coulomb's depends on charge and coulomb's law for attraction and repulsion.

If one of three lamps blows out when connected in series, what happens to the current in the other two?

None of the other lamps will work.

Which has more mass - a proton or an electron?

Proton.

Calculate the resistance of the filament in a light bulb that carries 0.4 A when 3.0 V is impressed across it.

R = V/I = (3.0 V) / (0.4 A) = 1.2 Ohms

In a normal atom, how many electrons are there compared with protons?

Same number but no net charge.

Why are the occupants safe inside a car struck by lightning?

The charges on the outside are mutually repelled and the electric fields inside cancel to zero.

How is the strength of an electric field indicated with field lines?

The closer the lines, the stronger the field.

If one of three lamps blows out when connected in parallel, what happens to the current in the other two?

The current in the other two will continue to flow.

If the voltage impressed across a circuit is constant but the resistance doubles, what change occurs in the current?

The current would be halved.

Why is that when gasoline is spilled on a wet surface, it is colorful?

The different colors correspond to the cancellations of their complementary colors by different thicknesses of the film. Interference of light waves.

How do the wave speeds compare for high-frequency and low-frequency electromagnetic waves?

There is only one speed (Speed of light) no matter the frequency, wavelength, or intensity of the radiation.

What condition is necessary for the flow of heat?

There needs to be a temperature difference for the flow of heat.

How do electric field lines directions compare with the direction of the force that acts on a positive test charge in the same region?

They are the same.

What do electric charges have have in common with magnetic poles?

They both attract and repel.

By how much is the electrical force between a pair of ions reduced when their separation distance is doubled? Tripled?

To 1/4; to 1/9

What analogous condition is necessary for the flow of charge?

Voltage difference is necessary for the flow of charge.

What is the size of the electric field inside any charged conductor?

Zero.

How can voltage be induced in a wire with the help of a magnet?

when there is relative motion between the coil and a magnet.