Physics Final Review

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second capacitance of 2C is connected in parallel with the first one, what happens to the time constant for the circuit?

It will increase.

Will plane waves incident upon a small opening in a barrier fan out on the other side, or continue on as plane waves?

They will fan out. They follow Huygens's principle.

What approximate wavelength of light corresponds to purple light?

400 nm

What approximate wavelength of light corresponds to green light?

550 nm

What approximate wavelength of light corresponds to red light?

700 nm

Explain the difference between a step up transformer and a step down transformer.

A step up transformer is one where the voltage on the secondary is larger than the voltage on the primary. A step down transformer is one where the voltage on the secondary is smaller than the voltage on the primary. A step up transformer has more coils in its secondary than its primary. A step down transformer has more coils in its primary than its secondary. A step up transformer reduces the current in the secondary, while a step down transformer increases the current in the secondary.

Will a lamp with a thick filament draw more or less current than a lamp with a thin filament?

A thick filament means a large cross sectional area. Resistance is directly proportional to cross sectional area. So larger area means larger resistance. And larger resistance means less current.

Explain the difference between a transverse and a longitudinal wave. Give an example of each type.

A transverse wave has the particles that make up the wave oscillating in the same direction of motion, while a transverse wave oscillates perpendicular to the direction of motion. An example of a longitudinal wave is sound. An example of a transverse wave is light.

Which of these is not a primary ray for a mirror? A. A ray that aims at the center of the mirror and is unaffected, continuing in a straight line after interacting with the mirror. B. A ray that comes in parallel to the optical axis, and then bends toward the focal point after interacting with the mirror. C. A ray that aims at the focal point, and then bends so that it is parallel to the optical axis after interacting with the mirror. D. A ray that strikes at the center of the mirror and bends following the law of reflection after interacting with the mirror. E. A ray that aims at the center of curvature of the mirror and bounces back along itself toward the object after interacting with the mirror.

A. A ray that aims at the center of the mirror and is unaffected, continuing in a straight line after interacting with the mirror.

A particular transformer has a primary current of 1.5 A and a secondary current of 1.5 μA. What kind of transformer would this be? a. Step-up transformer b. Step-down transformer c. It could be either type depending on the input voltage d. This is not possible with a transformer

A. step-up transformer

A resistor, capacitor, and switch are all connected in series to an ideal battery of constant terminal voltage. Initially, the switch is open. What is the voltage across the resistor and the capacitor a very long time after the switch is closed?

After a long time, the current has decayed to zero, so the resistor has a voltage drop of zero, while the capacitor has a voltage drop equivalent to the battery.

Everyone's vision is compromised underwater without goggles, but some can see a bit better than others. Which of the following individuals would have the clearest underwater vision? A. A person with vision that requires no correction. B. A person with myopia. C. A person with hyperopia. D. A person with presbyopia. E. A person with either C or D.

B. A person with myopia.

You have three materials that are transparent to light: gasoline (n = 1.4), lab-grown diamond (n = 2.41), and ice (n = 1.31). In which material does light travel the slowest? A. Gasoline B. Diamond C. Ice D. It would have the same speed in diamond and ice because they are solids. E. It would have the same speed in gasoline and lab-grown diamond because they are synthetic materials. F. It would have the same speed in all three materials.

B. Diamond

A current carrying wire is oriented perpendicular to the page, carrying its current out of the page. A magnetic field is oriented parallel to the page, downward. What is the direction of the force acting on this current carrying wire? A. Left B. Right C. Up D. Down E. Into the page F. Out of the page G. The force is zero

B. Right

In a typical DC circuit, which one of the following statements is true? a. The current in each branch of the circuit must be the same. b. The potential difference does not vary with time. c. The potential difference can only be provided by one battery. d. Any number of resistors can only be connected in parallel. e. The current in a single branch of the circuit may change direction during operation.

B. The potential difference does not vary with time.

A biologist changes the objective lens of a microscope, replacing a 20x objective with a 10x objective. To keep the magnification of the microscope the same, the focal length of the eyepiece must A. be doubled B. be halved C. Remain the same D. The magnification cannot stay the same if the objective power is changed.

B. be halved

Light passes through a 10-μm wide slit and is viewed on a screen 1m behind the slit. If the width of the slit is narrowed, the band of light will A. become narrower B. become wider C. remain about the same D. do either A or B, but it is impossible to know which

B. become wider

A cross section of a coil of wire is shown in the figure. If the north pole of the coil is on the right side, what is the direction of the current at the top side of the coil? a. Into the page b. Out of the page c. The current is zero d. Coils cannot have north poles.

B. out of the page

If you place a chunk of iron near the north pole of a magnet, attraction will occur. Why will attraction also occur if you place the same iron near the south pole of the magnet?

Because magnetic materials have the ability to align their inner magnetic domains to align with the external magnetic fields.

Along what axis does a plane mirror cause a reversal? A. Left/Right B. Up/Down C. Front/Back D. Plane mirrors do not cause reversals

C. Front/back

Two wires are made of the same material. One wire has twice the diameter of the other. How does the resistivity of thenarrow wire compare to that of the wide wire?A. The narrow wire's is four times as large. B. The narrow wire's is twice as large. C. They are equal. D. The narrow wire's is half as large. E. The narrow wire's is one quarter as large

C. They are equal

What are the two types of interference? When does each occur?

Constructive interference and destructive interference. Constructive interference occurs when two waves arrive at a location in phase (or have the same sign amplitude). Destructive interference occurs when two waves arrive at a location completely out of phase (or have opposite sign amplitudes).

Describe constructive interference.

Constructive interference occurs when two waves from different sources arrive in phase (meaning their crests and troughs occur at the same time). Constructive interference results in more amplitude of wave at the location than either of the individual waves.

Describe the conditions for forming a virtual image with mirrors.

Convex mirrors always create virtual images. A concave mirror will create a virtual image when the object is inside the focal length of the mirror.

You are observing your face in a cosmetic mirror. You note that your image is upright and enlarged. What kind of mirror created this image? Where is this image? A. A convex mirror. The image is in front of the surface of the mirror. B. A concave mirror. The image is in front of the surface of the mirror. C. A convex mirror. The image is behind the surface of the mirror. D. A concave mirror. The image is behind the surface of the mirror. E. Either a convex or concave, there's no way to know for sure. The image could be either in front or behind the surface of the mirror.

D. A concave mirror. The image behind the surface of the mirror.

A swatch of pure red fabric is viewed through a green filter. The fabric appears A. Red B. Green C. Yellow D. Black

D. Black

A single circular coil of wire connected to a galvanometer is lying flat on the table, as you view it from above. There is a magnetic field in this region that pokes out of the table, toward you. The magnetic field is reduced to zero over a period of20 seconds, and a clockwise current is measured using a galvanometer. The magnetic field is then increased back to its original value over a period of 10 seconds. What would the galvanometer read? A. The measured current would be larger, but in the same direction. B. The measured current would be smaller, but in the same direction. C. The measured current would be the same, but in the same direction. D. The measured current would be larger, but in the opposite direction. E. The measured current would be smaller, but in the opposite direction. F. The measured current would be the same, but in the opposite direction.

D. The measured current would be larger, but in the opposite direction.

You have a vacuum filled capacitor that can store charge Q when attached to a battery with terminal voltage V. If you wanted it to be able to store more charge in the capacitor, which of these changes could you make to improve how much charge is stored by the capacitor for the same voltage? a. Increase the area of the plates. b. Separate the plates. c. Insert a dielectric. d. More than one of the above. e. None of these.

D. more than one of the above

Which of the following waves requires a physical medium through which to travel? A. radio waves B. light C. x-rays D. sound E. gamma rays

D. sound

Describe destructive interference.

Destructive interference occurs when two waves from different sources arrive exactly out of phase (meaning one is at a crest while the other is at a trough). Destructive interference results in less amplitude of wave at the location than either of the individual waves.

Is diffraction more pronounced through a small opening or a large opening?

Diffraction is more pronounced through an opening comparable to the wavelength of the wave passing through it. Light will not diffract through a door, but radio waves might.

Describe the conditions for forming a virtual image with lenses.

Diverging lenses always create virtual images. A converging lens will create a virtual image when the object is inside the focal length of the lens.

If an object lies outside the focal point of a converging lens, which of the following statements about the image formed by this lens is true? A. The image is always real and magnified. B. The image could be real or virtual, depending on how far the object is past the focal point. C. The image could be upright or inverted, depending on how far the object is past the focal point. D. The image is always real and reduced. E. The image could be reduced or magnified, depending on how far the object is past the focal point.

E. The image could be reduced or magnified, depending on how far the object is past the focal point.

What is the error in saying that electrons in a common battery-driven circuit travel at about the speed of light?

Electrons cannot travel at the speed of light. The electrons begin to move, but they drift

True or False The wavelengths of visible waves are some of the longest electromagnetic waves.

False. They are small, on the order of hundreds of nanometers. Radio is among the longest wavelength.

Describe Faraday's law in your own words.

Faraday's law says that an emf is induced in a ring of current if the magnetic flux through the coil is changing.

Hyperopia

Hyperopia is farsightedness. Caused by either the eyeball being too short front to back, or the lens having to low a refractive index, so that light focuses behind the retina. A converging lens can be used to fix this condition.

A transformer has more coils in the secondary than it does in the primary coil. Would it increase or decrease the current in the secondary coil, compared to the first? Why?

If a transformer has more coils in its secondary coil, this makes it a step up transformer. That means it would increase the voltage, but decrease the current. So this means the current in the secondary would be smaller than the primary.

How does the current in the secondary of a transformer compare with the current in the primary when the secondary voltage is twice the primary voltage?

If the secondary voltage is twice the primary voltage, we are talking about a step up transformer. This means the current in the secondary is half the current in the primary.

In hospitals with magnetic resonance imaging (MRI) facilities and at other locations where large magnetic fields are present, there are usually signs warning people with pacemakers and other electronic medical devices not to enter. Why do you suspect this is?

If they move an object that can carry a current through a region of magnetic field, it might cause a current to flow in the device when not planned by the device, which could short it, causing damage to the human.

If you double the diameter of a wire, by what factor does the resistance change? Did it get larger or smaller?

If you double the diameter, the radius also doubles.

How does intensity relate to power?

Intensity is defined to be the power per unit area. So it is directly proportional to the power of the source.

What does it mean for two waves to be in phase?

It means they reach their crests and troughs at the same time.

A capacitor C is connected in series with a resistor R across a battery and an open switch. If a second resistor of 2R is connected in parallel with the first one, what happens to the time constant for the circuit?

It will decrease

Describe Lenz's law in your own words.

Lenz's law says that a magnetic field, and current, is induced in a ring of wire when the flux through the loop changes. The direction of this induced field is such that that would try to prevent any change to the already present magnetic field.

Does a diamond underwater sparkle more or less than in air?

Less

Myopia

Myopia is nearsightedness. Caused by either the eyeball being too long front to back, or the lens having too high a refractive index, so that light focuses in front of the retina. A diverging lens can be used to fix this condition.

Can an unmagnetized piece of material (that has magnetic properties) ever be repelled by a magnet?

No. Because the domains of magnetic materials always align with the external field, they cannot be repelled, only attracted. Similar to a neutral object always being attracted to a charged object.

Presbyopia

Presbyopia is the reduction in accommodation and lens flexibility that occurs with old age, resulting in farsightedness. A converging lens can be used to fix this condition.

Why are electrons rather than protons the charge carriers in a wire?

Protons are tightly bound in the nucleus and therefore difficult to remove. Valance electrons move as a "sea" inside conductors.

Explain the difference between resistance and resistivity.

Resistivity is the property of the metal conductor and does not change unless you change materials. It is a measure, essentially, of how often electrons run into other objects in the wire. Resistance can be adjusted by increasing or decreasing the length or cross-section of the wire.

What three quantities determine the size of the magnetic flux through a coil?

The area of the loop, the strength of the magnetic field, and the relative angle between the loop axis and the magnetic field.

What happens to the brightness of a lightbulb when the current through it increases? What causes this change?

The brightness increases. More current means more electrons running into more atoms causes more energy transfer. More energy transfer means more light radiated.

In what direction relative to the magnetic field must a charged particle move in order to have maximum deflecting force? What about minimum deflecting force?

The charged particle should move perpendicular to the magnetic field in order to maximize the force acting. If you want minimum force, the charged particle should move parallel, or anti-parallel to the magnetic field.

A resistor, capacitor, and switch are all connected in series to an ideal battery of constant terminal voltage. Initially, the switch is open. What is the voltage across the resistor and the capacitor at the fraction of a second after the switch is closed?

The current immediately jumps to a large value. So the resistor has the voltage drop of the battery, while the capacitor's voltage drop is zero, as no charge has had time to move to the plates.

Distinguish between the frequency, amplitude, period, and wavelength of a wave.

The frequency is how often the source oscillates. The period is the time for one oscillation. The amplitude is how far away from equilibrium the source oscillates. The wavelength is the distance between two wave crests.

Why are most transformers made with iron cores in their centers?

The iron core is able to magnetize, improving the magnetic field strength of the magnetic field created by the primary coil. A stronger magnetic field increases the flux through the secondary coil, making the effect of the changing field stronger than without the iron core.

The damaging effects of electric shock result from the amount of current that flows in the body. Why, then do we see signs that read "Danger - High Voltage" rather than "Danger - High Current"?

The potential difference is what drives the current, depending on the size of the resistor. If you make contact with a large potential difference, you don't necessarily draw a large current, it would depend on your resistance. So it makes more sense to warn of high voltage, since that would indicate the opportunity for large currents.

A proton moves in a circular path perpendicular to a magnetic field. If the field strength is increased, what happens to the radius of this path?

The radius and magnetic field are inversely proportional to one another. Therefore if the field strength increases, the radius of the particle decreases.

Red light has a longer wavelength than violet light. Which has a higher frequency?

The shorter wavelength has a higher frequency, that means violet light has a higher frequency than red light.

As you increased the frequency in each of the previous cases, what happened to the wavelength of the wave? What about when you decreased the frequency?

The wavelength decreased when the frequency increased. The wavelength increased when the frequency decreased.

In what way are magnetic poles very different from electric charges?

There can never be a single magnetic pole all by itself.

Do waves transfer matter from one location to another? What about energy? How do we know? (Think about the videos you just watched as you answer this question.)

They do not transfer matter. They do transfer energy. The pieces of the slinky near the person's hand do not move closer to the end of the slinky, but they do bunch up and un bunch as the wave passes through.

If two sources of waves are going to interfere constructively at some point in space, what is the condition for the difference in path between the two sources? What about for destructive interference?

To interfere constructively, the path difference must be an integer number of wavelengths. To interfere destructively, the path difference must be an integer number of wavelengths plus one half wavelength.

Is the rule for the interaction between magnetic poles similar to the rule for the interaction between electrically charged particles?

To some extent, yes. There are two pole types (North/South) and two charge types (Positive/Negative). Two like poles repel one another, just like two like charges repel one another. Two opposite poles attract one another, just like two opposite charges. It does seem to depend on distance in a similar way to how charges interact more strongly at close distances.

What is the condition for total internal reflection? Where must the light start? What kind of material must it be trying to enter?

Total internal reflection occurs when light tries to enter a material that has a smaller index of refraction than the material it is leaving. The light must start inside the high index material.

True or false The higher-frequency waves have shorter wavelengths than the lower-frequency waves.

True

True or false: A charged particle must move in a stationary magnetic field in order for that field to exert a force on it.

True. It is not possible to start a charge into motion with the magnetic field, since the force depends on the charge, the velocity, and the magnetic field strength.

What happens to the distance between two interference fringes if the separation between two slits is increased?

When you increase the slit spacing, the distance between adjacent fringes gets smaller. This is because the fringe spacing is inversely proportional to the slit spacing.

Can a transformer be made using a DC power supply? If not, why not? If so, what would you have to do to make it work?

Yes, but not efficiently. You would have to repeatedly turn the DC power supply on and off over and over, to continue to make the current in the primary coil change.

Can electromagnetic induction in a loop of wire be accomplished with a constant magnetic field? If not, why not? If so, how?

Yes. By rotating the coil within it, or by changing the area of the loop while it remains in the field.

Does it make a difference to the size of the induced current in the circuit (brightness of the bulb) if you move the bar magnet quickly vs slowly?

Yes. The faster you move the brighter the bulb. This is because the induced emf is inversely proportional to the time it takes to change the magnetic flux, according to Faraday's law. A larger emf (or voltage) induced means a larger current flows, making the bulb brighter.

Based on your observations in the simulation, does it make a difference to the direction of the induced current (+ or - on the voltmeter) if you move the bar magnet towards or away from the coil?

Yes. The voltmeter ticks to a different side of the meter when you move the magnet away from a coil than when you move it toward the coil. This means the current is flowing in a different direction.

Does it make a difference to the size of the induced current in the circuit (brightness of the bulb) if you move the bar magnet parallel to the coil axis, vs perpendicular to the coil axis?

Yes. You get a brighter bulb when moving parallel to the axis, compared to perpendicular to the axis. This is because when you move parallel to the coil axis, the magnetic flux change is larger.

If your laptop requires an input of 15 V, but your outlet only provides 120 V, what kind of transformer do you need?

You need a step down transformer, since the load (your lap top) requires a smaller voltage than the source (the wall outlet).

You are using a diffraction grating to observe a source that emits light across a wide section of the electromagnetic spectrum. As you look through the grating, which of these would demonstrate the least amount of spread away from the central maxima? (Assume that you are able to view or detect all wavelengths, not just the ones your eye could detect.)] a. Ultraviolet Light b. Red Light c. Violet Light d. Infrared Light e. Green Light

a. Ultraviolet Light

If your eye focuses light in front of your retina, what kind of lens might you need to correct your vision? a. Converging b. Diverging c. Either would work d. Neither would work

b. Diverging

A capacitor is filled with a Mylar dielectric (K = 3.0). You charge the capacitor fully using a battery.Then you remove the battery. If you then use insulating instruments to remove the dielectric from between the plates, what happens to the potential difference between the plates of the capacitor? a. The potential difference increases by a factor of 9. b. The potential difference increases by a factor of 3. c. The potential difference is unchanged. d. The potential difference decreases by a factor of 3. e. The potential difference decreases by a factor of 9.

b. The potential difference increases by a factor of 3.

A person has a near point of 55 cm. Where does the image of an object closer to them than 55 cm form? a. On the retina b. In front of the retina c. Behind the retina d. There is no image formed

c. Behind the retina

You are observing yourself in a fun-house mirror. In a particular section of the mirror, you see an enlarged image of your nose that is upright. What is the curvature of that section of the mirror, and how far from the mirror are you standing relative to the focal length? a. Concave mirror, outside the focal length b. Convex mirror, outside the focal length c. Concave mirror, inside the focal length d. Convex mirror, inside the focal length e. It could be more than one of the above

c. Concave mirror, inside the focal length

Below are five statements about virtual images. One of them is a false statement. Select the false statement. a. Virtual images cannot be projected on a screen. b. A plane mirror always forms a virtual image. c. Virtual images cannot be photographed. d. A diverging lens always forms a virtual image. e. It is possible to see virtual images with the naked eye.

c. Virtual images cannot be photographed.

If a real image created by a ______ mirror is located farther than 2f from the mirror, the object was between f and 2f from the mirror.

concave

Only ______ mirrors can create real images.

concave

Only ______ lenses can create real images.

converging

For what range of object locations will you observe a magnified image when looking into a concave mirror? a. Between the mirror and the focal point. b. Between the focal point and twice the focal point. c. Farther than twice the focal length. d. More than one of the above e. You cannot observe this kind of image with this mirror

d. More than one of the above

A current carrying wire is placed in a region where the magnetic field acts upwards (+y). If the force acting on the wire is out of the page (+z), what is the direction of the current in the wire? a. Left (-x) b. Up (+y) c. Out (+z) d. Right (+x) e. None of these

d. Right (+x)

To see the violet light in the primary rainbow, where did the light come from? a. The violet light comes from the absorption of all of the colors of the light other than violet. b. The violet light comes from the reflection of all of the colors of the light other than violet. c. The violet light comes from droplets higher up in the sky. d. The violet light comes from droplets lower in the sky. e. The violet light comes from many droplets both high and low in the sky.

d. The violet light comes from droplets lower in the sky.

A _______ type of lens is shown in the figure below. As parallel light rays pass through the lens from either side, they bend ______ the optical axis. (

diverging; away from

What kind of wave is sound? a. Transverse wave b. Longitudinal wave c. Mechanical wave d. Electromagnetic wave e. More than one of the above

e. More than one of the above

Light rays do not bend when traveling across a boundary for which the indexes of refraction are _______.

equal

If a real image created by a converging lens is located between f and 2f, the object was ______ than 2f from the lens.

farther

Rank the following electromagnetic waves from smallest to largest in terms of wavelength. radio ultraviolet x-rays visible light gamma rays microwave

gamma < x-rays < ultraviolet < visible < microwave < radio

Light rays bend farther from the normal axis when the light is traveling from a material with a _________ index of refraction into a material with a _______ index of refraction.

higher; lower

Light rays have a longer wavelength in materials where the index of refraction is ______.

lower

Light rays travel faster in materials where the index of refraction is _________.

lower

Light rays bend closer to the normal axis when the light is traveling from a material with a(n) ___________ index of refraction into a material with a(n) ________ index of refraction.

lower, higher

Rank the following electromagnetic waves from smallest to largest in terms of frequency.

radio < microwave < visible < ultraviolet < x-rays < gamma

A _______ image created by a lens appears on the opposite side of the lens.

real

A _______ image created by a mirror appears on the opposite side of the mirror.

virtual

The image created by a diverging lens or convex mirror is always ______, ______, and ______.

virtual, upright, and reduced