Physics Test Review #4

The electric power of a lamp that carries 2 A at 120 V is

240 W (P=IV)

What is the speed of light?

3 x 10^8 m/s

Suppose you walk toward a mirror at 2.0 m/s. How fast do you and your image approach each other?

4 m/s (you're moving at 2 m/s and the image is moving at 2 m/s so you add those together to get 4)

Given that the power consumed by a device is 700 W operating on a 170-V line, calculate the amount of current it draws.

4.1 A (P=IV)

When a 10-V battery is connected to a resistor, the current in the resistor is 2 A. What is the resistor's value?

5 ohms (V=IR)

Consider a circuit with a main wire that branches into two other wires. If the current is 10 A in the main wire and 4 A in one of the branches, how much current is in the other branch?

6 A (10-4)

A butterfly at eye level is 20 cm in front of a plane mirror. You are behind the butterfly, 50 cm from the mirror. What is the distance between your eye and the image of the butterfly in the mirror?

70 cm (image distance is always the same as object distance)

What does a changing magnetic field induce?

A changing electric field

Which warms more quickly in sunlight - a colorless or a colored piece of glass? Why?

A colored piece of glass warms quickest because it absorbs more frequencies of light, thus converting the energy to temperature.

What is the function of fuses or circuit breakers in a circuit?

A fuse is inserted into a circuit to protect the circuit from receiving too much current when shorted. A circuit breaker is the same function. - If a surge of current is evident through a line, the circuit breaker "breaks" the line, opening the flow of current. A fuse has to be replaced after one use while a circuit breaker can have several uses and is usually stronger.

What is a radiation curve?

A graph of brightness versus frequency

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

Battery produces dc while a power station generator produces ac

Your friend says that a battery supplies the electrons in an electric circuit. Do you agree or disagree?

Disagree. All matter has atoms, all atoms have electrons. What the battery does, is supply the potential difference to make existing electrons move.

What is meant by saying charge is conserved?

Electric charge can neither be created nor destroyed. The net quantity of electric charge, the amount of positive charge minus the amount of negative charge in the universe, is always same.

Are electrons or protons the principal charge carries in metal wires?

Electrons, as the outer shell electrons are loosely bound to the atom. As a result, they can "move" within a wire.

The intensity of light decreases as the inverse square of the distance from the source. Does this mean that light energy is lost? Explain.

Energy is spread out and diluted, but not "lost." In accord with the inverse-square law, light intensity gets weaker with distance, but the total amount of light over a spherical surface is the same at all distances from the source.

Why are metals shiny?

Free electrons in metals vibrate when light strikes them, thereby reemitting the light as reflected light.

Why do wet objects normally look darker than the same objects when dry?

Light bounces around inside the transparent water region covering a wet object, getting absorbed more on each bounce.

The fundamental rule for the attraction and repulsion of magnets is _______.

Like poles repel each other and opposite poles attract.

If you look with a magnifying glass at pictures printed in full color in this or other books or magazines, you'll notice three colors of ink plus black. What are these colors?

Magenta, cyan, and yellow

What are the subtractive primary colors?

Magenta, cyan, and yellow

If the sunlight were somehow green instead of white, what color clothing would be most advisable on an uncomfortable hot day? On a very cold day?

White or green for a hot day (reflection). Magenta for a cold day (absorb).

What is the color of the peak frequency of solar radiation when it is plotted versus wavelength?

Yellow-green

Is a current-carrying wire electrically charged because of the electrons moving in it?

Yes, because there is the movement of charge

The north pole of a compass is attracted to the north magnetic pole of Earth, yet like poles repel. Can you resolve this apparent dilemma?

Yes, the Earth's north magnetic pole is really the south pole of a magnet.

Does the law of reflection hold for curved mirrors? Explain.

Yes. It is as if the curved mirror is made of many small plane mirrors at slightly different orientations to each other.

Can a surface be considered polished for some waves and not for others? Cite an example.

Yes. The mesh of a radio dish is polished for long wavelength radio waves and yet rough for short wavelength light waves.

When you look at a distant galaxy through a telescope, how is it that you're looking backward in time?

You are seeing the delay for the light to reach your eye.

When combing your hair, you scuff electrons from your hair onto the comb. Is your hair then positively or negatively charged? How about the comb?

Your hair will have a positive charge and the comb will have a negative charge

The unit of electric charge, the coulomb, is the charge on

a specific large number of electrons

What is the relationship between the direction of traveling rays of light and the line representing the wave crests?

The direction of the rays of light is perpendicular to the line representing the wave crests.

Magnetic domains are composed of clustered _______

aligned iron atoms

The field surrounding every moving electron is

always both electric and magnetic.

Moving electric charges will interact with

an electric field or a magnetic field

A magnifying glass widens the angle through which _________.

an object is viewed

If a steady magnetic field exerts a force on a moving charge, that force is directed

at right angles to the direction of the field.

The source of electrons lighting an incandescent ac light bulb is

atoms in the light bulb filament

An electron and a proton

attract each other

Which has the higher frequency, red light or blue light?

blue light

What factors does the resistance offered by a piece of conductor depend upon?

both the geometry and the material of the conductor

Electric potential, measured in volts, is the ratio of electric energy to amount of electric

charge

The magnetic field about a straight length of current-carrying wire is _______.

circular in shape

The electrical force between charges is strongest when the charges are

close together

As more lamps are put into a series circuit, the overall current in the power source

decreases In a parallel circuit, the more lamps there are, the higher the current will be.

How does wetness affect the resistance of your body?

decreases your resistance

What kind of glasses would you wear while watching 3D movies, and why?

glasses with one horizontally polarized and one vertically polarized lens, because one projector is horizontally polarized and the other is vertically polarized

To connect a pair of resistors so that their combined (equivalent) resistance will be greater than the resistance of either one, should you connect them in series or in parallel?

in series Connecting them in parallel will make the overall resistance less than the resistance of either one.

What part of the electromagnetic spectrum is most absorbed by water?

infrared

Magnetic domains normally occur in

iron

Alternating current is normally produced by a

generator

To say that an object is electrically polarized is to say

its charges have been rearranged.

The electrical force between charges depends only on the charges'

magnitude and separation distance

The electromagnetic waves having the highest speed in free space are _________

none in particular; gamma, radio, and light have the same speed

An iron nail is more strongly attracted to the _____ pole.

north or south pole - no difference really

Several paper clips dangle from the north pole of a magnet. The induced pole in the bottom of the lowermost paper clip is a

north pole

A wire carrying a current is normally charged

not at all

The force that acts on a current-carrying wire placed in a magnetic field is _______.

perpendicular in direction to the magnetic field

Strip electrons from an atom and the atom becomes a

positive ion

A positive ion has more

protons than electrons

What is the color of visible light of the lowest frequencies? Of the highest frequencies?

red ... violet

A main difference between gravitational and electric forces is that electrical forces

repel or attract

A difference between electric forces and gravitational forces is that gravitational forces are not affected by

repulsive interaction

The magnetic field about Earth takes a shape _______.

similar to that of an interior bar magnet

Compared to the amount of electric current in the filament of a lamp, the amount of current in the connecting wire is

the same

There are electrons in the filament of the ac lamp in your bedroom. When you turn on the lamp and it glows, the glowing comes from

the same electrons

When we say charge is conserved, we mainly mean that charge can be _______.

transferred without loss, like money in a bank

The electric resistance in a length of wire is doubled when the wire is _______.

twice as long

If you plug an electric toaster rated at 110 V into a 220-V outlet, the current in the toaster will be about

twice what it should be

In what region of the electromagnetic spectrum is the resonant frequency of electrons in glass?

ultraviolet

Electric potential, unlike electric potential energy, is measured in units of _______.

volts

Which pole of a compass needle points to a south pole of a magnet?

the north pole

What color results when red is subtracted from white light?

Cyan

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

1a (the same current flows through lamps in a series circuit)

Why are red, green, and blue called the additive primary colors?

Adding appropriate amounts of red plus green plus blue lights can produce almost any color of the spectrum.

Your friend says that microwaves and ultraviolet light have different wavelengths but travel through space at the same speed. Do you agree or disagree?

Agree

The wattage marked on a light bulb is not an inherent property of the bulb, but depends on the voltage to which it is connected, usually 110 or 120 V. How many amperes flow through a 58-W bulb connected in a 120-V circuit?

0.48 (P=IV)

What is a positive ion? A negative ion?

A negative ion (anion) has more electrons than protons, leading to a net negative electrical charge. A positive ion (cation) has fewer electrons than protons, thus leading to a net positive charge.

Does a viewer see a single color or a spectrum of colors coming from a single faraway drop?

A viewer sees a single color from a single faraway drop.

Distinguish between a virtual image and a real image. Mention in each case whether the image made by a single lens is right-side up or inverted.

A virtual image, unlike a real image, cannot be displayed on a screen. A virtual image is upright, whereas a real image is inverted.

How does the charge of one electron compare to that of another electron? How does it compare with the charge of a proton?

All electrons have negative charge, but of different magnitude. All protons have positive charge, but of different magnitude.

What produces an electromagnetic wave?

An oscillating or accelerating electric charge

Are automobile headlights wired in parallel or in series? What is your evidence?

Auto headlights are wired in parallel. When one burns out, the other remains lit.

Why is it safe to remain inside a car during a lightning storm?

Because of the metal frame. It serves as a conductor of electricity and channels the lightning away into the ground without impacting anyone inside the car.; this is known as a Faraday cage.

Does charge flow through a circuit or into a circuit? Does voltage flow through a circuit, or is voltage established across a circuit?

Charge flows through a circuit while voltage is established across a circuit

At the micro level, what is the difference between an unmagnetized iron nail and a magnetized iron nail?

In an unmagnetized iron nail the atoms electrons are not aligned. In a magnetized iron nail they are aligned

How does incident light that falls on an object affect the motion of electrons in the atoms of the object?

Incident light makes the electrons oscillate. The electrons then emit light or absorb the light and convert it to heat.

What happens to light when it falls upon a material that has a natural frequency equal to the frequency of the light? What if it's above or below the frequency of light?

It is absorbed It is remitted (reflected)

In which medium does light travel faster - thin air or dense air? How does this affect the length of daylight hours?

It travels faster in thin air, which makes sunlight curve and extends the length of the day.

Many dry cereals are fortified with iron, which is added to the cereal in the form of small iron particles. How might these particles be separated from the cereal?

Many dry cereals are fortified with iron, which is added to the cereal in the form of small iron particles. How might these particles be separated from the cereal?

What is normally the net charge of an atom?

Neutral (or no net charge)

Coulomb's law is most similar to which law?

Newton's law of gravity

Why does the Sun look reddish at sunrise and sunset but not at noon?

Only the low-frequency red light penetrates the thick layers of atmosphere at sunset/sunrise because of the longer path length of sunlight.

What are the principal differences between a radio wave and light? Between light and an X-ray?

Radio waves have a lower frequency and longer wavelength than visible light waves. Light waves have a lower frequency and longer wavelength than X-rays.

Why does a rainbow look like a curve when viewed from the ground?

Raindrops act like prisms that reflect the colors of light in particular angles depending on how the individual colors are bent by the prism. Light seen at that angle forms a bow shape.

What color light is transmitted through a piece of red glass?

Red

Is a mirage the result of reflection or refraction? Why does it happen?

Refraction. Light curves through warm, low-density air near the ground, where it travels faster.

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

Serves as a ground connection

How much energy is supplied to each coulomb of charge that flows through a 12-v battery?

Since Voltage is the amount of energy in joules per coulomb of charge, 12 Volts will yield 12 joules of energy per coulomb of charge.

Which requires a physical medium in which to travel: light, sound, or both?

Sound requires a physical medium while light does not.

Cite the law of reflection.

The angle of incidence equals the angle of reflection.

How does the average speed of light in glass compare with its speed in a vacuum?

The average speed of light in glass is about 67% of the speed of light in a vacuum.

What happens to the brightness of light emitted by a light bulb when the current flowing through it increases?

The bulb will glow brighter

When a car veers off the road such that the left front wheel goes off the pavement into the gravel before the right wheel, what will happen to the car, and why?

The car will tend to turn to the left. Because the left wheel hits the gravel first and slows down before the right wheel, the right wheel covers a greater distance, causing the car to turn to the left.

What is the effect on the color of a cloud when it contains an abundance of large droplets?

The cloud becomes dark

Why are there probably no permanently aligned magnetic domains in Earth's core?

The core is too hot to allow atoms to maintain a constant magnetic orientation.

When you double the distance between a pair of charged particles, what happens to the force between them? Does it depend on the sign of the charges?

The force reduces to 1/4, whatever the sign of charge

Why is the sky blue when the Sun is overhead?

The molecules in the atmosphere scatter blue light more than any other light, so the sky looks blue. Also, the air molecules have resonances in the ultraviolet, so they scatter blue light more than red light.

What happens when light from the Sun interacts with the molecules of the atmosphere?

The molecules scatter the light

What part of an atom is positively charged and what part is negatively charged?

The nucleus of an atom is positively charged and the electrons have a negative charge.

Why are objects with vast numbers of electrons normally not electrically charged?

The objects aren't charged because the vast number of electrons is equal to the vast number of protons.

Why is it inadvisable to make a horseshoe magnet from a flexible material?

The poles of the magnet attract each other and cause the magnet to bend, even enough for the poles to touch if the material is flexible enough

What would the rainbow look like to a viewer in the sky, and why?

The rainbow would appear to be a complete circle, because Earth no longer obstructs our view when we are above.

How does the resistance of a thick piece of copper wire compare to the resistance of a thin piece of copper wire?

The resistance of the thin piece is greater than that of the thick piece.

How do the rods in the eye differ from the cones?

The rods are rod-shaped and are more sensitive to dim light. The cones are cone-shaped and are color-sensitive.

What happens to the speed of light waves when they enter water from air?

The speed decreases

Distinguish between a converging lens and a diverging lens.

When two parallel rays of light pass through a converging lens, the rays bend towards each other. When they pass through a diverging lens, the rays move apart from each other.

You're explaining to a youngster at the seashore why the water is cyan colored. The youngster points to the white caps of overturning waves and asks why they are white. What is your answer?

The white caps have different sized water drops that scatter many frequencies of light. The combination of scattered light appears white.

When white light strikes a prism, what happens and why?

The white light emerges with the colors separated, with the red light bending the least.

How are the magnetic domains of a non-magnetized chunk of iron oriented?

They are oriented randomly.

How does the frequency of a radio wave compare to the frequency of the vibrating electrons that produce it?

They are the same

Why are red and cyan called complementary colors?

They can be added together to make white light.

Why are thick wires rather than thin wires usually used to carry large currents?

Thick wires have less resistance and so they will heat up less when a large current is passed through them. The resistance of a wire is proportional to its length and inversely proportional to its cross-sectional area.

Are eyeglasses made with "high index of refraction" materials thinner or thicker? Why?

Thinner. Light bends more entering high index of refraction materials.

When one material is rubbed against another, electrons jump readily from one to the other but protons do not. Why is this? (Think in atomic terms.)

This is because protons are fixed in place and are not allowed to more from atom to atom while, electron are not fixed in place and can easily move from atom to atom

Light normally travels in straight lines, but it "bends" in an optical fiber. Explain.

Total internal reflection keeps the light trapped inside the optical fiber.

True or False: Objects illuminated by moonlight lack color. The light reflected by objects in the moonlight is most often too dim to stimulate the color-perceiving cones in the eye. So we see these objects primarily with our rods, which explains their lack of color.

True

Which has the shorter wavelengths: ultraviolet or infrared? Which has the higher frequency?

Ultraviolet light has shorter wavelength and higher frequency than infrared radiation.

What is the fate of the energy in ultraviolet light that is incident upon glass?

Ultraviolet light will be absorbed by the resonant vibration of electrons and turned into internal energy and a temperature increase.

Why do opaque materials become warmer when light shines on them?

Vibrations given by the light to their electrons, atoms, and molecules that absorb the light become internal energy, thus leading to a temperature increase.

What accounts for the whiteness of a cloud?

Water droplets of different sizes scatter a variety of light frequencies, resulting in a white cloud.

What happens to the wavelength and frequency of the light waves as they enter water from air?

Wavelength decreases, and frequency will stay the same.

When is the angle at which a ray of light strikes glass not the same as the angle it exits?

When the light strikes the glass in one medium (such as air) and exits the glass in another medium (such as water)

When you remove your wool suit from the dry cleaner's garment bag, the bag becomes positively charged. Explain how this occurs.

When the wool and plastic rub against each other, electrons are rubbed from the plastic onto the wool. The deficiency of electrons on the plastic bag results in its positive charge.

A balloon will stick to a wooden wall if the balloon is charged

either positively or negatively

Every proton in the universe is surrounded by its own

electric field and gravitational field

Which force binds atoms together to form molecules?

electrical

A proton and an electron are placed in an electric field. Which undergoes the greater acceleration?

electron

In an electrically neutral atom the number of protons in the nucleus is equal to the number of

electrons that surround the nucleus

Electric power in a circuit is the rate at which _______.

energy dissipates

Compared to the huge force that attracts an iron tack to a strong magnet, the force that the tack exerts on the magnet is

equally huge

Magnet A has twice the magnetic field strength of Magnet B and at a certain distance pulls on magnet B with a force of 100 N. The amount of force that magnet B exerts on magnet A is

exactly 100 N

Short wavelengths of visible light interact more frequently with the atoms in glass than do longer wavelengths. Does this interaction time tend to speed up or to slow down the average speed of short-wavelength light in glass?

slow down

What kinds of molecules scatter high frequencies of light? Low frequencies?

small molecules high molecules

Two protons attract each other gravitationally and repel each other electrically. By far the greater force is

the electrical repulsion

A glass marble is rubbed against a piece of silk. As a result the piece of fabric acquires extra electrons. What happens to the glass marble?

the marble has lost the same number of electrons acquired by the piece of silk ..... the marble acquires a positive charge and attracts the piece of silk